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• How to handle encryption key conflicts when synchronizing data?

  - by Rafael

  Assume that there is data that gets synchronized between several devices. The data is protected with a symmetric encryption algorithm and a key. The key is stored on each device and encrypted with a password. When a user changes the password only the key gets re-encrypted. Under normal circumstances, when there is a good network connection to other peers, the current key gets synchronized and all data on the new device gets encrypted with the same key. But how to handle situations where a new device doesn’t have a network connection and e.g. creates its own new, but incompatible key? How to keep the usability as high as possible under such circumstances? The application could detect that there is no network and hence refuse to start. That’s very bad usability in my opinion, because the application isn’t functional at all in this case. I don’t consider this a solution. The application could ignore the missing network connection and create a new key. But what to do when the application gains a network connection? There will be several incompatible keys and some parts of the underlying data could only be encrypted with one key and other parts with another key. The situation would get worse if there would be more keys than just two and the application would’ve to ask every time for a password when another object that should get decrypted with another key would be needed. It is very messy and time consuming to try to re-encrypt all data that is encrypted with another key with a main key. What should be the main key at all in this case? The oldest key? The key with the most encrypted objects? What if the key got synchronized but not all objects that got encrypted with this particular key? How should the user know for which particular password the application asks and why it takes probably very long to re-encrypt the data? It’s very hard to describe encryption “issues” to users. So far I didn’t find an acceptable solution, nor some kind of generic strategy. Do you have some hints about a concrete strategy or some books / papers that describe synchronization of symmetrically encrypted data with keys that could cause conflicts?

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• Create a kind of Interface c++ [migrated]

  - by Liuka

  I'm writing a little 2d rendering framework with managers for input and resources like textures and meshes (for 2d geometry models, like quads) and they are all contained in a class "engine" that interacts with them and with a directX class. So each class have some public methods like init or update. They are called by the engine class to render the resources, create them, but a lot of them should not be called by the user: //in pseudo c++ //the textures manager class class TManager { private: vector textures; .... public: init(); update(); renderTexture(); //called by the "engine class" loadtexture(); gettexture(); //called by the user } class Engine { private: Tmanager texManager; public: Init() { //initialize all the managers } Render(){...} Update(){...} Tmanager* GetTManager(){return &texManager;} //to get a pointer to the manager //if i want to create or get textures } In this way the user, calling Engine::GetTmanager will have access to all the public methods of Tmanager, including init update and rendertexture, that must be called only by Engine inside its init, render and update functions. So, is it a good idea to implement a user interface in the following way? //in pseudo c++ //the textures manager class class TManager { private: vector textures; .... public: init(); update(); renderTexture(); //called by the "engine class" friend class Tmanager_UserInterface; operator Tmanager_UserInterface*(){return reinterpret_cast<Tmanager_UserInterface*>(this)} } class Tmanager_UserInterface : private Tmanager { //delete constructor //in this class there will be only methods like: loadtexture(); gettexture(); } class Engine { private: Tmanager texManager; public: Init() Render() Update() Tmanager_UserInterface* GetTManager(){return texManager;} } //in main function //i need to load a texture //i always have access to Engine class engine-GetTmanger()-LoadTexture(...) //i can just access load and get texture; In this way i can implement several interface for each object, keeping visible only the functions i (and the user) will need. There are better ways to do the same?? Or is it just useless(i dont hide the "framework private functions" and the user will learn to dont call them)? Before i have used this method: class manager { public: //engine functions userfunction(); } class engine { private: manager m; public: init(){//call manager init function} manageruserfunciton() { //call manager::userfunction() } } in this way i have no access to the manager class but it's a bad way because if i add a new feature to the manager i need to add a new method in the engine class and it takes a lot of time. sorry for the bad english.

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• Quaternion based rotation and pivot position

  - by Michael IV

  I can't figure out how to perform matrix rotation using Quaternion while taking into account pivot position in OpenGL.What I am currently getting is rotation of the object around some point in the space and not a local pivot which is what I want. Here is the code [Using Java] Quaternion rotation method: public void rotateTo3(float xr, float yr, float zr) { _rotation.x = xr; _rotation.y = yr; _rotation.z = zr; Quaternion xrotQ = Glm.angleAxis((xr), Vec3.X_AXIS); Quaternion yrotQ = Glm.angleAxis((yr), Vec3.Y_AXIS); Quaternion zrotQ = Glm.angleAxis((zr), Vec3.Z_AXIS); xrotQ = Glm.normalize(xrotQ); yrotQ = Glm.normalize(yrotQ); zrotQ = Glm.normalize(zrotQ); Quaternion acumQuat; acumQuat = Quaternion.mul(xrotQ, yrotQ); acumQuat = Quaternion.mul(acumQuat, zrotQ); Mat4 rotMat = Glm.matCast(acumQuat); _model = new Mat4(1); scaleTo(_scaleX, _scaleY, _scaleZ); _model = Glm.translate(_model, new Vec3(_pivot.x, _pivot.y, 0)); _model =rotMat.mul(_model);//_model.mul(rotMat); //rotMat.mul(_model); _model = Glm.translate(_model, new Vec3(-_pivot.x, -_pivot.y, 0)); translateTo(_x, _y, _z); notifyTranformChange(); } Model matrix scale method: public void scaleTo(float x, float y, float z) { _model.set(0, x); _model.set(5, y); _model.set(10, z); _scaleX = x; _scaleY = y; _scaleZ = z; notifyTranformChange(); } Translate method: public void translateTo(float x, float y, float z) { _x = x - _pivot.x; _y = y - _pivot.y; _z = z; _position.x = _x; _position.y = _y; _position.z = _z; _model.set(12, _x); _model.set(13, _y); _model.set(14, _z); notifyTranformChange(); } But this method in which I don't use Quaternion works fine: public void rotate(Vec3 axis, float angleDegr) { _rotation.add(axis.scale(angleDegr)); // change to GLM: Mat4 backTr = new Mat4(1.0f); backTr = Glm.translate(backTr, new Vec3(_pivot.x, _pivot.y, 0)); backTr = Glm.rotate(backTr, angleDegr, axis); backTr = Glm.translate(backTr, new Vec3(-_pivot.x, -_pivot.y, 0)); _model =_model.mul(backTr);///backTr.mul(_model); notifyTranformChange(); }

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• Contract / Project / Line-Item hierarchy design considerations

  - by Ryan

  We currently have an application that allows users to create a Contract. A contract can have 1 or more Project. A project can have 0 or more sub-projects (which can have their own sub-projects, and so on) as well as 1 or more Line. Lines can have any number of sub-lines (which can have their own sub-lines, and so on). Currently, our design contains circular references, and I'd like to get away from that. Currently, it looks a bit like this: public class Contract { public List<Project> Projects { get; set; } } public class Project { public Contract OwningContract { get; set; } public Project ParentProject { get; set; } public List<Project> SubProjects { get; set; } public List<Line> Lines { get; set; } } public class Line { public Project OwningProject { get; set; } public List ParentLine { get; set; } public List<Line> SubLines { get; set; } } We're using the M-V-VM "pattern" and use these Models (and their associated view models) to populate a large "edit" screen where users can modify their contracts and the properties on all of the objects. Where things start to get confusing for me is when we add, for example, a Cost property to the Line. The issue is reflecting at the highest level (the contract) changes made to the lowest level. Looking for some thoughts as to how to change this design to remove the circular references. One thought I had was that the contract would have a Dictionary<Guid, Project> which would contain ALL projects (regardless of their level in hierarchy). The Project would then have a Guid property called "Parent" which could be used to search the contract's dictionary for the parent object. THe same logic could be applied at the Line level. Thanks! Any help is appreciated.

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• SFX Played Once per Collision or Hit

  - by David Dimalanta

  I have a question about using Box2D (engine for LibGDX used to make realistic physics). I observed on the code that I've made for the physics here below: @Override public boolean touchUp(int screenX, int screenY, int pointer, int button) { // TODO Touch Up Event if(is_Next_Fruit_Touched) { BodyEditorLoader Fruit_Loader = new BodyEditorLoader(Gdx.files.internal("Shape_Physics/Fruity Physics.json")); Fruit_BD.type = BodyType.DynamicBody; Fruit_BD.position.set(x, y); FixtureDef Fruit_FD = new FixtureDef(); // --> Allows you to make the object's physics. Fruit_FD.density = 1.0f; Fruit_FD.friction = 0.7f; Fruit_FD.restitution = 0.2f; MassData mass = new MassData(); mass.mass = 5f; Fruit_Body[n] = world.createBody(Fruit_BD); Fruit_Body[n].setActive(true); // --> Let your dragon fall. Fruit_Body[n].setMassData(mass); Fruit_Body[n].setGravityScale(1.0f); System.out.println("Eggs... " + n); Fruit_Loader.attachFixture(Fruit_Body[n], Body, Fruit_FD, Fruit_IMG.getWidth()); Fruit_Origin = Fruit_Loader.getOrigin(Body, Fruit_IMG.getWidth()).cpy(); is_Next_Fruit_Touched = false; up = y; Gdx.app.log("Initial Y-coordinate", "Y at " + up); //Once it's touched, the next fruit will set to drag. if(n < 50) { n++; }else{ System.exit(0); } } return true; } Now, I'm thinking which part o line should I implement for the sound effects. My objectives to make SFX played once for every collision (Or should I say "SFX played once per collision"?) on the following: SFX played once if they hit on the objects of its kind. (e.g. apple vs. apple) SFX played once on a different sound when it hit on the ground. (e.g. apple land on the mud) Take note that I'm using Box2D for the Java programming version thanks to LibGDX via Box2D engine and I edited the physics body using Physics Body Editor before I implement it to code. I tried to check every available methods for body, fixture definition, or body definition to code for the SFX when hit but it seems only for the gravity and weight. Is there possibly available on the document for SFX played when collision happens if possible?

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• Behaviour Trees with irregular updates

  - by Robominister

  I'm interested in behaviour trees that aren't iterated every game tick, but every so often. (Edit: the tree could specify how many frames within the main game loop to wait before running its tick function again). Every theoretical implementation I have seen of behaviour trees talks of the tree search being carried out every game update - which seems necessary, because a leaf node (eg a behaviour, like 'return to base') needs to be constantly checked to see if is still running, failed or completed. Can anyone suggest how I might start implementing a tree that isnt run every tick, or point me in the direction of good material specific to this case (I am struggling to find anything)? My thoughts so far: action leaf nodes (when they start) must only push some kind of action object onto a list for an entity, rather than directly calling any code that makes the entity do something. The list of actions for the entity would be run every frame (update any that need to run, pop any that have completed from the list). the return state from a given action must be fed back into the tree, so that when we run the tree iteration again (and reach the same action leaf node - so the tree has so far determined that we ought to still be trying this action) - that the action has completed, or is still running etc. If my actual action code is running from an action list on an entity, then I possibly need to cancel previously running actions in the list - i am thinking that I can just delete the entire stack of queued up actions. I've seen the idea of ActionLists which block lower priority actions when a higher priority one is added, but this seems like very close logic to behaviour trees, and I dont want to be duplicating behaviour. This leaves me with some questions 1) How would I feed the action return state back into the tree? Its obvious I need to store some information relating to 'currently executing actions' on the entity, and check that in the tree tick, but I can't imagine how. 2) Does having a seperate behaviour tree (for deciding behaviour) and action list (for carrying out actual queued up actions) sound like a reasonable approach? 3) Is the approach of updating a behaviour tree irregularly actually used by anyone? It seems like a nice idea for budgeting ai search time when you have a lot of ai entities to process. (Edit) - I am also thinking about storing a single instance of a given behaviour tree in memory, and providing it by reference to any entity that uses it. So any information about what action was last selected for execution on an entity must be stored in a data context relative to the entity (which the tree can check). (I am probably answering my own questions as i go!) I hope I have expressed my questions adequately! Thanks in advance for any help :)

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• How to keep a data structure synchronized over a network?

  - by David Gouveia

  Context In the game I'm working on (a sort of a point and click graphic adventure), pretty much everything that happens in the game world is controlled by an action manager that is structured a bit like: So for instance if the result of examining an object should make the character say hello, walk a bit and then sit down, I simply spawn the following code: var actionGroup = actionManager.CreateGroup(); actionGroup.Add(new TalkAction("Guybrush", "Hello there!"); actionGroup.Add(new WalkAction("Guybrush", new Vector2(300, 300)); actionGroup.Add(new SetAnimationAction("Guybrush", "Sit")); This creates a new action group (an entire line in the image above) and adds it to the manager. All of the groups are executed in parallel, but actions within each group are chained together so that the second one only starts after the first one finishes. When the last action in a group finishes, the group is destroyed. Problem Now I need to replicate this information across a network, so that in a multiplayer session, all players see the same thing. Serializing the individual actions is not the problem. But I'm an absolute beginner when it comes to networking and I have a few questions. I think for the sake of simplicity in this discussion we can abstract the action manager component to being simply: var actionManager = new List<List<string>>(); How should I proceed to keep the contents of the above data structure syncronized between all players? Besides the core question, I'm also having a few other concerns related to it (i.e. all possible implications of the same problem above): If I use a server/client architecture (with one of the players acting as both a server and a client), and one of the clients has spawned a group of actions, should he add them directly to the manager, or only send a request to the server, which in turn will order every client to add that group? What about packet losses and the like? The game is deterministic, but I'm thinking that any discrepancy in the sequence of actions executed in a client could lead to inconsistent states of the world. How do I safeguard against that sort of problem? What if I add too many actions at once, won't that cause problems for the connection? Any way to alleviate that?

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• C# OpenGL problem with animation

  - by user3696303

  there is a program that simulates a small satellite and requires that a rotation animation of the satellite along the three axes. But when you try to write an animation problem during compilation: the program simply closes (shutdown occurs when swapbuffers, mainloop, redisplay), when you write the easiest programs have the same problem arose. Trying to catch exception by try-catch but here is not exception. How to solve this? I suffer with this a few days. Work in c# visual studio 2008 framework namespace WindowsFormsApplication6 { public partial class Form1 : Form { public Form1() { try { InitializeComponent(); AnT1.InitializeContexts(); } catch(Exception) { Glut.glutDisplayFunc(Draw); Glut.glutTimerFunc(50, Timer, 0); Glut.glutMainLoop(); } } void Timer(int Unused) { Glut.glutPostRedisplay(); Glut.glutTimerFunc(50, Timer, 0); } private void AnT1_Load(object sender, EventArgs e) { Glut.glutInit(); Glut.glutInitDisplayMode(Glut.GLUT_RGB | Glut.GLUT_DOUBLE | Glut.GLUT_DEPTH); Gl.glClearColor(255, 255, 255, 1); Gl.glViewport(0, 0, AnT1.Width, AnT1.Height); Gl.glMatrixMode(Gl.GL_PROJECTION); Gl.glLoadIdentity(); Glu.gluPerspective(45, (float)AnT1.Width / (float)AnT1.Height, 0.1, 200); Gl.glMatrixMode(Gl.GL_MODELVIEW); Gl.glLoadIdentity(); Gl.glEnable(Gl.GL_DEPTH_TEST); Gl.glClear(Gl.GL_COLOR_BUFFER_BIT | Gl.GL_DEPTH_BUFFER_BIT); Gl.glPushMatrix(); double xy = 0.2; Gl.glTranslated(xy, 0, 0); xy += 0.2; Draw(); Glut.glutSwapBuffers(); Glut.glutPostRedisplay(); Gl.glPushMatrix(); Draw(); Gl.glPopMatrix(); } void Draw() { Gl.glLoadIdentity(); Gl.glColor3f(0.502f, 0.502f, 0.502f); Gl.glTranslated(-1, 0, -6); Gl.glRotated(95, 1, 0, 0); Glut.glutSolidCylinder(0.7, 2, 60, 60); Gl.glLoadIdentity(); Gl.glColor3f(0, 0, 0); Gl.glTranslated(-1, 0, -6); Gl.glRotated(95, 1, 0, 0); Glut.glutWireCylinder(0.7, 2, 20, 20); } } }

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• ssao implementation

  - by Irbis

  I try to implement a ssao based on this tutorial: link I use a deferred rendering and world coordinates for shading calculations. When saving gbuffer a vertex shader output looks like this: worldPosition = vec3(ModelMatrix * vec4(inPosition, 1.0)); normal = normalize(normalModelMatrix * inNormal); gl_Position = ProjectionMatrix * ViewMatrix * ModelMatrix * vec4(inPosition, 1.0); Next for a ssao calculations I render a scene as a full screen quad and I save an occlusion parameter in a texture. (Vertex positions in the world space: link Normals in the world space: link) SSAO implementation: subroutine (RenderPassType) void ssao() { vec2 texCoord = CalcTexCoord(); vec3 worldPos = texture(texture0, texCoord).xyz; vec3 normal = normalize(texture(texture1, texCoord).xyz); vec2 noiseScale = vec2(screenSize.x / 4, screenSize.y / 4); vec3 rvec = texture(texture2, texCoord * noiseScale).xyz; vec3 tangent = normalize(rvec - normal * dot(rvec, normal)); vec3 bitangent = cross(normal, tangent); mat3 tbn = mat3(tangent, bitangent, normal); float occlusion = 0.0; float radius = 4.0; for (int i = 0; i < kernelSize; ++i) { vec3 pix = tbn * kernel[i]; pix = pix * radius + worldPos; vec4 offset = vec4(pix, 1.0); offset = ProjectionMatrix * ViewMatrix * offset; offset.xy /= offset.w; offset.xy = offset.xy * 0.5 + 0.5; float sample_depth = texture(texture0, offset.xy).z; float range_check = abs(worldPos.z - sample_depth) < radius ? 1.0 : 0.0; occlusion += (sample_depth <= pix.z ? 1.0 : 0.0); } outputColor = vec4(occlusion, occlusion, occlusion, 1); } That code gives following results: camera looking towards -z world space: link camera looking towards +z world space: link I wonder if it is possible to use world coordinates in the above code ? When I move camera I get different results because world space positions don't change. Can I treat worldPos.z as a linear depth ? What should I change to get a correct results ? I except the white areas in place of occlusion, so the ground should has the white areas only near to the object.

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• Why does my ID3DXSprite appear to be incorrectly scaled?

  - by Bjoern

  I am using D3D9 for rendering some simple things (a movie) as the backmost layer, then on top of that some text messages, and now wanted to add some buttons to that. Before adding the buttons everything seemed to have worked fine, and I was using a ID3DXSprite for the text as well (ID3DXFont), now I am loading some graphics for the buttons, but they seem to be scaled to something like 1.2 times their original size. In my test window I centered the graphic, but it being too big it just doesnt fit well, for example the client area is 640x360, the graphic is 440, so I expect 100 pixel on left and right, left side is fine [I took screenshot and "counted" the pixels in photoshop], but on the right there is only about 20 pixels) My rendering code is very simple (I am omitting error checks, et cetera, for brevity) // initially viewport was set to width/height of client area // clear device m_d3dDevice->Clear( 0, NULL, D3DCLEAR_TARGET|D3DCLEAR_STENCIL|D3DCLEAR_ZBUFFER, D3DCOLOR_ARGB(0,0,0,0), 1.0f, 0 ); // begin scene m_d3dDevice->BeginScene(); // render movie surface (just two triangles to which the movie is rendered) m_d3dDevice->SetRenderState(D3DRS_ALPHABLENDENABLE,false); m_d3dDevice->SetSamplerState( 0, D3DSAMP_MAGFILTER, D3DTEXF_LINEAR ); // bilinear filtering m_d3dDevice->SetSamplerState( 0, D3DSAMP_MINFILTER, D3DTEXF_LINEAR ); // bilinear filtering m_d3dDevice->SetTextureStageState( 0, D3DTSS_COLORARG1, D3DTA_TEXTURE ); m_d3dDevice->SetTextureStageState( 0, D3DTSS_COLORARG2, D3DTA_DIFFUSE ); //Ignored m_d3dDevice->SetTextureStageState( 0, D3DTSS_COLOROP, D3DTOP_SELECTARG1 ); m_d3dDevice->SetTexture( 0, m_movieTexture ); m_d3dDevice->SetStreamSource(0, m_displayPlaneVertexBuffer, 0, sizeof(Vertex)); m_d3dDevice->SetFVF(Vertex::FVF_Flags); m_d3dDevice->DrawPrimitive(D3DPT_TRIANGLELIST, 0, 2); // render sprites m_sprite->Begin(D3DXSPRITE_ALPHABLEND | D3DXSPRITE_SORT_TEXTURE | D3DXSPRITE_DO_NOT_ADDREF_TEXTURE); // text drop shadow m_font->DrawText( m_playerSprite, m_currentMessage.c_str(), m_currentMessage.size(), &m_playerFontRectDropShadow, DT_RIGHT|DT_TOP|DT_NOCLIP, m_playerFontColorDropShadow ); // text m_font->DrawText( m_playerSprite, m_currentMessage.c_str(), m_currentMessage.size(), &m_playerFontRect, DT_RIGHT|DT_TOP|DT_NOCLIP, m_playerFontColorMessage ) ); // control object m_sprite->Draw( m_texture, 0, 0, &m_vecPos, 0xFFFFFFFF ); // draws a few objects like this m_sprite->End() // end scene m_d3dDevice->EndScene(); What did I forget to do here? Except for the control objects (play button, pause button etc which are placed on a "panel" which is about 440 pixels wide) everything seems fine, the objects are positioned where I expect them, but just too big. By the way I loaded the images using D3DXCreateTextureFromFileEx (resizing wnidow, and reacting to lost device, etc, works fine too). For experimenting, I added some code to take an identity matrix and scale is down on the x/y axis to 0.75f, which then gave me the expected result for the controls (but also made the text smaller and out of position), but I don't know why I would need to scale anything. My rendering code is so simple, I just wanted to draw my 2D objects 1;1 the size they came from the file... I am really very inexperienced in D3D, so the answer might be very simple...

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• Antenna Aligner Part 5: Devil is in the detail

  - by Chris George

  "The first 90% of a project takes 90% of the time and the last 10% takes the another 200%"  (excerpt from onista) Now that I have a working app (more or less), it's time to make it pretty and slick. I can't stress enough how useful it is to get other people using your software, and my simple app is no exception. I handed my iPhone to a couple of my colleagues at Red Gate and asked them to use it and give me feedback. Immediately it became apparent that the delay between the list page being shown and the list being drawn was too long, and everyone who tried the app clicked on the "Recalculate" button before it had finished. Similarly, selecting a transmitter heralded a delay before the compass page appeared with similar consequences. All users expected there to be some sort of feedback/spinny etc. to show them it is actually doing something. In a similar vein although for opposite reasons, clicking the Recalculate button did indeed recalculate the available transmitters and redraw them, but it did this too fast! One or two users commented that they didn't know if it had done anything. All of these issues resulted in similar solutions; implement a waiting spinny. Thankfully, jquery mobile has one built in, primarily used for ajax operations. Not wishing to bore you with the many many iterations I went through trying to get this to work, I'll just give you my solution! (Seriously, I was working on this most evenings for at least a week!) The final solution for the recalculate problem came in the form of the code below. $(document).on("click", ".show-page-loading-msg", function () {            var $this = $(this),                theme = $this.jqmData("theme") ||                        $.mobile.loadingMessageTheme;            $.mobile.showPageLoadingMsg(theme, "recalculating", false);            setTimeout(function ()                           { $.mobile.hidePageLoadingMsg(); }, 2000);            getLocationData();        })        .on("click", ".hide-page-loading-msg", function () {              $.mobile.hidePageLoadingMsg();        }); The spinny is activated by setting the class of a button (for example) to the 'show-page-loading-msg' class. &lt;a data-role="button" class="show-page-loading-msg"Recalculate This means the code above is fired, calling the showPageLoadingMsg on the document.mobile object. Then, after a 2 second timeout, it calls the hidePageLoadingMsg() function. Supposedly, it should show "recalculating" underneath the spinny, but I've not got that to work. I'm wondering if there is a problem with the jquery mobile implementation. Anyway, it doesn't really matter, it's the principle I'm after, and I now have spinnys!

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• C# Dev - I've tried Lisps, but I don't get it.

  - by Jonathan Mitchem

  After a few months of learning about and playing with lisps, both CL and a bit of Clojure, I'm still not seeing a compelling reason to write anything in it instead of C#. I would really like some compelling reasons, or for someone to point out that I'm missing something really big. The strengths of a Lisp (per my research): Compact, expressive notation - More so than C#, yes... but I seem to be able to express those ideas in C# too. Implicit support for functional programming - C# with LINQ extension methods: mapcar = .Select( lambda ) mapcan = .Select( lambda ).Aggregate( (a,b) = a.Union(b) ) car/first = .First() cdr/rest = .Skip(1) .... etc. Lambda and higher-order function support - C# has this, and the syntax is arguably simpler: "(lambda (x) ( body ))" versus "x = ( body )" "#(" with "%", "%1", "%2" is nice in Clojure Method dispatch separated from the objects - C# has this through extension methods Multimethod dispatch - C# does not have this natively, but I could implement it as a function call in a few hours Code is Data (and Macros) - Maybe I haven't "gotten" macros, but I haven't seen a single example where the idea of a macro couldn't be implemented as a function; it doesn't change the "language", but I'm not sure that's a strength DSLs - Can only do it through function composition... but it works Untyped "exploratory" programming - for structs/classes, C#'s autoproperties and "object" work quite well, and you can easily escalate into stronger typing as you go along Runs on non-Windows hardware - Yeah, so? Outside of college, I've only known one person who doesn't run Windows at home, or at least a VM of Windows on *nix/Mac. (Then again, maybe this is more important than I thought and I've just been brainwashed...) The REPL for bottom-up design - Ok, I admit this is really really nice, and I miss it in C#. Things I'm missing in a Lisp (due to a mix of C#, .NET, Visual Studio, Resharper): Namespaces. Even with static methods, I like to tie them to a "class" to categorize their context (Clojure seems to have this, CL doesn't seem to.) Great compile and design-time support the type system allows me to determine "correctness" of the datastructures I pass around anything misspelled is underlined realtime; I don't have to wait until runtime to know code improvements (such as using an FP approach instead of an imperative one) are autosuggested GUI development tools: WinForms and WPF (I know Clojure has access to the Java GUI libraries, but they're entirely foreign to me.) GUI Debugging tools: breakpoints, step-in, step-over, value inspectors (text, xml, custom), watches, debug-by-thread, conditional breakpoints, call-stack window with the ability to jump to the code at any level in the stack (To be fair, my stint with Emacs+Slime seemed to provide some of this, but I'm partial to the VS GUI-driven approach) I really like the hype surrounding Lisps and I gave it a chance. But is there anything I can do in a Lisp that I can't do as well in C#? It might be a bit more verbose in C#, but I also have autocomplete. What am I missing? Why should I use Clojure/CL?

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• root issues in softwarecenter, synaptic and update manager

  - by user188977

  i have a notebook samsung ativ 2 and ubuntu 12.04 precise, cinnamon desktop. after logging in today my update manager, synaptic and ubuntu softwarecenter stopped working. synaptic i can only launch from terminal the others from panel.when choosing to update, nothing happens. same thing when trying to install programms from syn. or softw.center.when launching softwarec. from terminal i get: marcus@ddddddddd:~$ software-center 2013-11-10 22:30:46,206 - softwarecenter.ui.gtk3.app - INFO - setting up proxy 'None' 2013-11-10 22:30:46,217 - softwarecenter.db.database - INFO - open() database: path=None use_axi=True use_agent=True (software-center:4772): Gtk-WARNING **: Theme parsing error: softwarecenter.css:34:20: Not using units is deprecated. Assuming 'px'. (software-center:4772): Gtk-WARNING **: Theme parsing error: softwarecenter.css:34:22: Not using units is deprecated. Assuming 'px'. (software-center:4772): Gtk-WARNING **: Theme parsing error: softwarecenter.css:56:20: Not using units is deprecated. Assuming 'px'. (software-center:4772): Gtk-WARNING **: Theme parsing error: softwarecenter.css:56:22: Not using units is deprecated. Assuming 'px'. (software-center:4772): Gtk-WARNING **: Theme parsing error: softwarecenter.css:60:20: Not using units is deprecated. Assuming 'px'. (software-center:4772): Gtk-WARNING **: Theme parsing error: softwarecenter.css:60:22: Not using units is deprecated. Assuming 'px'. 2013-11-10 22:30:46,977 - softwarecenter.backend.reviews - WARNING - Could not get usefulness from server, no username in config file 2013-11-10 22:30:47,320 - softwarecenter.ui.gtk3.app - INFO - show_available_packages: search_text is '', app is None. 2013-11-10 22:30:48,057 - softwarecenter.db.pkginfo_impl.aptcache - INFO - aptcache.open() 2013-11-10 22:31:00,646 - softwarecenter.fixme - WARNING - logs to the root logger: '('/usr/share/software-center/softwarecenter/utils.py', 201, 'get_title_from_html')' 2013-11-10 22:31:00,645 - root - WARNING - failed to parse: '<div style="background-color: #161513; width:1680px; height:200px;">  <div style="background: url('/site_media/exhibits/2013/09/AAMFP_Leaderboard_700x200_1.jpg') top left no-repeat; width:700px; height:200px;"></div> </div>' ('ascii' codec can't encode character u'\xa0' in position 70: ordinal not in range(128)) 2013-11-10 22:31:02,268 - softwarecenter.db.update - INFO - skipping region restricted app: 'Comentarios Web' (not whitelisted) 2013-11-10 22:31:02,769 - softwarecenter.db.update - INFO - skipping region restricted app: 'reEarCandy' (not whitelisted) 2013-11-10 22:31:04,821 - softwarecenter.db.update - INFO - skipping region restricted app: 'Flaggame' (not whitelisted) 2013-11-10 22:31:05,622 - softwarecenter.db.update - INFO - skipping region restricted app: 'Bulleti d'esquerra de Calonge i Sant Antoni ' (not whitelisted) 2013-11-10 22:31:08,352 - softwarecenter.ui.gtk3.app - INFO - software-center-agent finished with status 0 2013-11-10 22:31:08,353 - softwarecenter.db.database - INFO - reopen() database 2013-11-10 22:31:08,353 - softwarecenter.db.database - INFO - open() database: path=None use_axi=True use_agent=True 2013-11-10 22:33:32,319 - softwarecenter.backend - WARNING - _on_trans_error: org.freedesktop.PolicyKit.Error.Failed: ('system-bus-name', {'name': ':1.72'}): org.debian.apt.install-or-remove-packages 2013-11-10 22:36:01,818 - softwarecenter.backend - WARNING - daemon dies, ignoring: <AptTransaction object at 0x48e4b40 (aptdaemon+client+AptTransaction at 0x645aaa0)> exit-failed 2013-11-10 22:36:01,820 - softwarecenter.db.pkginfo_impl.aptcache - INFO - aptcache.open()

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• Savable in Widget Lookup on Move Action

  - by Geertjan

  Possible from 7.3 onwards, since Widget now implements Lookup.Provider for the first time: import java.awt.Point; import java.io.IOException; import org.netbeans.api.visual.action.ActionFactory; import org.netbeans.api.visual.action.MoveProvider; import org.netbeans.api.visual.widget.LabelWidget; import org.netbeans.api.visual.widget.Scene; import org.netbeans.api.visual.widget.Widget; import org.netbeans.spi.actions.AbstractSavable; import org.openide.util.Lookup; import org.openide.util.lookup.AbstractLookup; import org.openide.util.lookup.InstanceContent; import org.openide.windows.TopComponent; public class MyWidget extends LabelWidget { private MySavable mySavable; private Lookup lookup; private TopComponent tc; private InstanceContent ic; public MyWidget(Scene scene, String label, TopComponent tc) { super(scene, label); this.tc = tc; ic = new InstanceContent(); getActions().addAction(ActionFactory.createMoveAction(null, new MoveStrategyProvider())); } @Override public Lookup getLookup() { if (lookup == null) { lookup = new AbstractLookup(ic); } return lookup; } private class MoveStrategyProvider implements MoveProvider { @Override public void movementStarted(Widget widget) { } @Override public void movementFinished(Widget widget) { modify(); } @Override public Point getOriginalLocation(Widget widget) { return ActionFactory.createDefaultMoveProvider().getOriginalLocation(widget); } @Override public void setNewLocation(Widget widget, Point point) { ActionFactory.createDefaultMoveProvider().setNewLocation(widget, point); } } private void modify() { if (getLookup().lookup(MySavable.class) == null) { ic.add(mySavable = new MySavable()); } } private class MySavable extends AbstractSavable { public MySavable() { register(); } TopComponent tc() { return tc; } @Override protected String findDisplayName() { return getLabel(); } @Override protected void handleSave() throws IOException { ic.remove(mySavable); unregister(); } @Override public boolean equals(Object obj) { if (obj instanceof MySavable) { MySavable m = (MySavable) obj; return tc() == m.tc(); } return false; } @Override public int hashCode() { return tc().hashCode(); } } }

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• How to perform Cross Join with Linq

  - by berthin

  Cross join consists to perform a Cartesian product of two sets or sequences. The following example shows a simple Cartesian product of the sets A and B: A (a1, a2) B (b1, b2) => C (a1 b1,            a1 b2,            a2 b1,            a2, b2 ) is the Cartesian product's result. Linq to Sql allows using Cross join operations. Cross join is not equijoin, means that no predicate expression of equality in the Join clause of the query. To define a cross join query, you can use multiple from clauses. Note that there's no explicit operator for the cross join. In the following example, the query must join a sequence of Product with a sequence of Pricing Rules: 1: //Fill the data source 2: var products = new List<Product> 3: { 4: new Product{ProductID="P01",ProductName="Amaryl"}, 5: new Product {ProductID="P02", ProductName="acetaminophen"} 6: }; 7:  8: var pricingRules = new List<PricingRule> 9: { 10: new PricingRule {RuleID="R_1", RuleType="Free goods"}, 11: new PricingRule {RuleID="R_2", RuleType="Discount"}, 12: new PricingRule {RuleID="R_3", RuleType="Discount"} 13: }; 14: 15: //cross join query 16: var crossJoin = from p in products 17: from r in pricingRules 18: select new { ProductID = p.ProductID, RuleID = r.RuleID };   Below the definition of the two entities using in the above example.   1: public class Product 2: { 3: public string ProductID { get; set; } 4: public string ProductName { get; set; } 5: } 1: public class PricingRule 2: { 3: public string RuleID { get; set; } 4: public string RuleType { get; set; } 5: }   Doing this: 1: foreach (var result in crossJoin) 2: { 3: Console.WriteLine("({0} , {1})", result.ProductID, result.RuleID); 4: }   The output should be similar on this:   ( P01   -    R_1 )   ( P01   -    R_2 )   ( P01   -    R_3 )   ( P02   -    R_1 )   ( P02   -    R_2 )   ( P02   -    R_3) Conclusion Cross join operation is useful when performing a Cartesian product of two sequences object. However, it can produce very large result sets that may caused a problem of performance. So use with precautions :)

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• Why do I always think I know much less than others? [closed]

  - by John Kenedy

  I have been in programming since primary 6. Since the time DOS comes, I have been doing programming in quickbasic 4.5, then to VB 6, then to C#. In between I also do programming in C++. But every time I open Stack Overflow and trying to help others answering their problems, it seems that I know nothing. I feel that I am so stupid even I have been in programming for so long. I would shock reading all the questions and unable to find any clue. Is technology moving too fast that left out me? I feel that technology changes too fast and I can't keep up, when I know ASP.NET web form, MVC is out, when I know MVC, android/iphone/HTML5 app is popular. It seems that I am chasing something and never reach 'it'. I don't know whether this is correct place for me to talk about this. I just wish to listen to opinion like you, how do you think technology should grow instead of recreating language, adding bug here and there to let programmer figure it out, while big company share the solution among themselves. This is exactly how I feel. The simple example is how do you think why doesn't Dictionary<> in .NET provide iterating the object using index? Why must we use Key or GetEnumerator(). Developer has to google and read wasted hour of hour of time to find pieces of hack code to use reflection to achieve reading from index. Where developer will keep it as collection and valuable code. HOwever when times come, everything changes again, developer has to find answer for new silly problems again! Yes, I really hate it! I hate how many big companies are playing with the developer by cutting a big picture into small puzzle and messing it up and asking developer to place it together themselves. As if they are creating problems for us to solve it, so we are unable to grow upfront, we are being manipulated by those silly problems they have created. Another sample would how difficult to collect Cookies from CookieContainer without passing the URL, yes without the URL and I WANT to get all cookie in the cookiecontainer without knowing the URL, I want to iterate all. Why does micros0ft have to limit me from doing that?

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• 2D Collision in Canvas - Balls Overlapping When Velocity is High

  - by kushsolitary

  I am doing a simple experiment in canvas using Javascript in which some balls will be thrown on the screen with some initial velocity and then they will bounce on colliding with each other or with the walls. I managed to do the collision with walls perfectly but now the problem is with the collision with other balls. I am using the following code for it: //Check collision between two bodies function collides(b1, b2) { //Find the distance between their mid-points var dx = b1.x - b2.x, dy = b1.y - b2.y, dist = Math.round(Math.sqrt(dx*dx + dy*dy)); //Check if it is a collision if(dist <= (b1.r + b2.r)) { //Calculate the angles var angle = Math.atan2(dy, dx), sin = Math.sin(angle), cos = Math.cos(angle); //Calculate the old velocity components var v1x = b1.vx * cos, v2x = b2.vx * cos, v1y = b1.vy * sin, v2y = b2.vy * sin; //Calculate the new velocity components var vel1x = ((b1.m - b2.m) / (b1.m + b2.m)) * v1x + (2 * b2.m / (b1.m + b2.m)) * v2x, vel2x = (2 * b1.m / (b1.m + b2.m)) * v1x + ((b2.m - b1.m) / (b2.m + b1.m)) * v2x, vel1y = v1y, vel2y = v2y; //Set the new velocities b1.vx = vel1x; b2.vx = vel2x; b1.vy = vel1y; b2.vy = vel2y; } } You can see the experiment here. The problem is, some balls overlap each other and stick together while some of them rebound perfectly. I don't know what is causing this issue. Here's my balls object if that matters: function Ball() { //Random Positions this.x = 50 + Math.random() * W; this.y = 50 + Math.random() * H; //Random radii this.r = 15 + Math.random() * 30; this.m = this.r; //Random velocity components this.vx = 1 + Math.random() * 4; this.vy = 1 + Math.random() * 4; //Random shade of grey color this.c = Math.round(Math.random() * 200); this.draw = function() { ctx.beginPath(); ctx.fillStyle = "rgb(" + this.c + ", " + this.c + ", " + this.c + ")"; ctx.arc(this.x, this.y, this.r, 0, Math.PI*2, false); ctx.fill(); ctx.closePath(); } }

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• Ubuntu 11.10 crashes all browsers often

  - by murat

  I have been using ubuntu 11.10 for 1 year,today it made me surprised. When I open google chrome it just closes itself. Firstly i thought that it is just for chrome and tried Firefox : It also closes itself and one thing more : I tried desktop programs such as image viewer it also closes itself.I restarted it but there is no changing.What can do this ? is it virus or another system problem ? I did not have any problem like this until today.. $ google-chrome (google-chrome:7064): Gtk-WARNING **: Unable to locate theme engine in module_path: "pixmap", (google-chrome:7064): Gtk-WARNING **: Unable to locate theme engine in module_path: "pixmap", (google-chrome:7064): Gtk-WARNING **: Unable to locate theme engine in module_path: "pixmap", (google-chrome:7064): Gtk-WARNING **: Unable to locate theme engine in module_path: "pixmap", --2012-04-04 19:33:14-- https://clients2.google.com/cr/report Resolving clients2.google.com... 173.194.70.100, 173.194.70.101, 173.194.70.102, ... Connecting to clients2.google.com|173.194.70.100|:443... connected. HTTP request sent, awaiting response... 200 OK Length: unspecified [text/html] 2012-04-04 19:33:19 (888 KB/s) - `/dev/fd/3' saved [16] (exe:7166): Gtk-WARNING **: Unable to locate theme engine in module_path: "pixmap", (exe:7166): Gtk-WARNING **: Unable to locate theme engine in module_path: "pixmap", (exe:7166): Gtk-WARNING **: Unable to locate theme engine in module_path: "pixmap", (exe:7166): Gtk-WARNING **: Unable to locate theme engine in module_path: "pixmap", Moonlight: 3.99.0.3 Moonlight: Attempting to load libmoonloaderxpi (exe:7201): Gtk-WARNING **: Unable to locate theme engine in module_path: "pixmap", (exe:7201): Gtk-WARNING **: Unable to locate theme engine in module_path: "pixmap", (exe:7201): Gtk-WARNING **: Unable to locate theme engine in module_path: "pixmap", (exe:7201): Gtk-WARNING **: Unable to locate theme engine in module_path: "pixmap", Failed to open VDPAU backend libvdpau_nvidia.so: cannot open shared object file: No such file or directory Segmentation fault After trying to install libvdpau1 error is changed : google-chrome --2012-04-04 20:05:03-- https://clients2.google.com/cr/report Resolving clients2.google.com... 173.194.70.113, 173.194.70.138, 173.194.70.139, ... Connecting to clients2.google.com|173.194.70.113|:443... connected. HTTP request sent, awaiting response... Moonlight: 3.99.0.3 Moonlight: Attempting to load libmoonloaderxpi 200 OK Length: unspecified [text/html] Saving to: `/dev/fd/3' [<=> ] 0 --.-K/s f4c55117d1b4656e [ <= ] 16 --.-K/s in 0s 2012-04-04 20:05:12 (337 KB/s) - `/dev/fd/3' saved [16] Segmentation fault

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• Binding MediaElement to a ViewModel in a Windows 8 Store App

  - by jdanforth

  If you want to play a video from your video-library in a MediaElement control of a Metro Windows Store App and tried to bind the Url of the video file as a source to the MediaElement control like this, you may have noticed it’s not working as well for you: <MediaElement Source="{Binding Url}" /> I have no idea why it’s not working, but I managed to get it going using  ContentControl instead: <ContentControl Content="{Binding Video}" /> The code behind for this is: protected override void OnNavigatedTo(NavigationEventArgs e) {     _viewModel = new VideoViewModel("video.mp4");     DataContext = _viewModel; } And the VideoViewModel looks like this: public class VideoViewModel {     private readonly MediaElement _video;     private readonly string _filename;       public VideoViewModel(string filename)     {         _filename = filename;         _video = new MediaElement { AutoPlay = true };         //don't load the stream until the control is ready         _video.Loaded += VideoLoaded;     }       public MediaElement Video     {         get { return _video; }     }       private async void VideoLoaded(object sender, RoutedEventArgs e)     {         var file = await KnownFolders.VideosLibrary.GetFileAsync(_filename);         var stream = await file.OpenAsync(FileAccessMode.Read);         _video.SetSource(stream, file.FileType);     } } I had to wait for the MediaElement.Loaded event until I could load and set the video stream.

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• So, I though I wanted to learn frontend/web development and break out of my comfort zone...

  - by ripper234

  I've been a backend developer for a long time, and I really swim in that field. C++/C#/Java, databases, NoSql, caching - I feel very much at ease around these platforms/concepts. In the past few years, I started to taste end-to-end web programming, and recently I decided to take a job offer in a front end team developing a large, complex product. I wanted to break out of my comfort zone and become more of an "all around developer". Problem is, I'm getting more and more convinced I don't like it. Things I like about backend programming, and missing in frontend stuff: More interesting problems - When I compare designing a server that handle massive data, to adding another form to a page or changing the validation logic, I find the former a lot more interesting. Refactoring refactoring refactoring - I am addicted to Visual Studio with Resharper, or IntelliJ. I feel very comfortable writing code as it goes without investing too much thought, because I know that with a few clicks I can refactor it into beautiful code. To my knowledge, this doesn't exist at all in javascript. Intellisense and navigation - I hate looking at a bunch of JS code without instantly being able to know what it does. In VS/IntelliJ I can summon the documentation, navigate to the code, climb up inheritance hiererchies ... life is sweet. Auto-completion - Just hit Ctrl-Space on an object to see what you can do with it. Easier to test - With almost any backend feature, I can use TDD to capture the requirements, see a bunch of failing tests, then implement, knowing that if the tests pass I did my job well. With frontend, while tests can help a bit, I find that most of the testing is still manual - fire up that browser and verify the site didn't break. I miss that feeling of "A green CI means everything is well with the world." Now, I've only seriously practiced frontend development for about two months now, so this might seem premature ... but I'm getting a nagging feeling that I should abandon this quest and return to my comfort zone, because, well, it's so comfy and fun. Another point worth mentioning in this context is that while I am learning some frontend tools, a lot of what I'm learning is our company's specific infrastructure, which I'm not sure will be very useful later on in my career. Any suggestions or tips? Do you think I should give frontend programming "a proper chance" of at least six to twelve months before calling it quits? Could all my pains be growing pains, and will they magically disappear as I get more experienced? Or is gaining this perspective is valuable enough, even if plan to do more "backend stuff" later on, that it's worth grinding my teeth and continuing with my learning?

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• How to get around the Circular Reference issue with JSON and Entity

  - by DanScan

  I have been experimenting with creating a website that leverages MVC with JSON for my presentation layer and Entity framework for data model/database. My Issue comes into play with serializing my Model objects into JSON. I am using the code first method to create my database. When doing the code first method a one to many relationship (parent/child) requires the child to have a reference back to the parent. (Example code my be a typo but you get the picture) class parent { public List<child> Children{get;set;} public int Id{get;set;} } class child { public int ParentId{get;set;} [ForeignKey("ParentId")] public parent MyParent{get;set;} public string name{get;set;} } When returning a "parent" object via a JsonResult a circular reference error is thrown because "child" has a property of class parent. I have tried the ScriptIgnore attribute but I lose the ability to look at the child objects. I will need to display information in a parent child view at some point. I have tried to make base classes for both parent and child that do not have a circular reference. Unfortunately when I attempt to send the baseParent and baseChild these are read by the JSON Parser as their derived classes (I am pretty sure this concept is escaping me). Base.baseParent basep = (Base.baseParent)parent; return Json(basep, JsonRequestBehavior.AllowGet); The one solution I have come up with is to create "View" Models. I create simple versions of the database models that do not include the reference to the parent class. These view models each have method to return the Database Version and a constructor that takes the database model as a parameter (viewmodel.name = databasemodel.name). This method seems forced although it works. NOTE:I am posting here because I think this is more discussion worthy. I could leverage a different design pattern to over come this issue or it could be as simple as using a different attribute on my model. In my searching I have not seen a good method to overcome this problem. My end goal would be to have a nice MVC application that heavily leverages JSON for communicating with the server and displaying data. While maintaining a consistant model across layers (or as best as I can come up with).

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• Switch from back-end to front-end programming: I'm out of my comfort zone, should I switch back?

  - by ripper234

  I've been a backend developer for a long time, and I really swim in that field. C++/C#/Java, databases, NoSql, caching - I feel very much at ease around these platforms/concepts. In the past few years, I started to taste end-to-end web programming, and recently I decided to take a job offer in a front end team developing a large, complex product. I wanted to break out of my comfort zone and become more of an "all around developer". Problem is, I'm getting more and more convinced I don't like it. Things I like about backend programming, and missing in frontend stuff: More interesting problems - When I compare designing a server that handle massive data, to adding another form to a page or changing the validation logic, I find the former a lot more interesting. Refactoring refactoring refactoring - I am addicted to Visual Studio with Resharper, or IntelliJ. I feel very comfortable writing code as it goes without investing too much thought, because I know that with a few clicks I can refactor it into beautiful code. To my knowledge, this doesn't exist at all in javascript. Intellisense and navigation - I hate looking at a bunch of JS code without instantly being able to know what it does. In VS/IntelliJ I can summon the documentation, navigate to the code, climb up inheritance hiererchies ... life is sweet. Auto-completion - Just hit Ctrl-Space on an object to see what you can do with it. Easier to test - With almost any backend feature, I can use TDD to capture the requirements, see a bunch of failing tests, then implement, knowing that if the tests pass I did my job well. With frontend, while tests can help a bit, I find that most of the testing is still manual - fire up that browser and verify the site didn't break. I miss that feeling of "A green CI means everything is well with the world." Now, I've only seriously practiced frontend development for about two months now, so this might seem premature ... but I'm getting a nagging feeling that I should abandon this quest and return to my comfort zone, because, well, it's so comfy and fun. Another point worth mentioning in this context is that while I am learning some frontend tools, a lot of what I'm learning is our company's specific infrastructure, which I'm not sure will be very useful later on in my career. Any suggestions or tips? Do you think I should give frontend programming "a proper chance" of at least six to twelve months before calling it quits? Could all my pains be growing pains, and will they magically disappear as I get more experienced? Or is gaining this perspective is valuable enough, even if plan to do more "backend stuff" later on, that it's worth grinding my teeth and continuing with my learning?

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• My image is not showing in java, using ImageIcon

  - by user1048606

  I'd like to know why my images are now showing up when I use ImageIcon and when I have specified the directory the image is in. All I get is a black blank screen with nothing else on it. import java.awt.Image; import java.awt.event.KeyEvent; import javax.swing.ImageIcon; import java.awt.Image; import java.awt.event.KeyEvent; import java.util.ArrayList; import javax.swing.ImageIcon; // Class for handling key input public class Craft { private int dx; private int dy; private int x; private int y; private Image image; private Image image2; private ArrayList missiles; private final int CRAFT_SIZE = 20; private String craft = "C:\\Users\\Jimmy\\Desktop\\Jimmy's Folder\\programs\\craft.png"; public Craft() { ImageIcon ii = new ImageIcon(craft); image2 = ii.getImage(); missiles = new ArrayList(); x = 40; y = 60; } public void move() { x += dx; y += dy; } public int getX() { return x; } public int getY() { return y; } public Image getImage() { return image; } public ArrayList getMissiles() { return missiles; } public void keyPressed(KeyEvent e) { int key = e.getKeyCode(); // Shooting key if (key == KeyEvent.VK_SPACE) { fire(); } if (key == KeyEvent.VK_LEFT) { dx = -1; } if (key == KeyEvent.VK_RIGHT) { dx = 1; } if (key == KeyEvent.VK_UP) { dy = -1; } if (key == KeyEvent.VK_DOWN) { dy = 1; } } // Handles the missile object firing out of the ship public void fire() { missiles.add(new Missile(x + CRAFT_SIZE, y + CRAFT_SIZE/2)); } public void keyReleased(KeyEvent e) { int key = e.getKeyCode(); if (key == KeyEvent.VK_LEFT) { dx = 0; } if (key == KeyEvent.VK_RIGHT) { dx = 0; } if (key == KeyEvent.VK_UP) { dy = 0; } if (key == KeyEvent.VK_DOWN) { dy = 0; } } }

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• How to refactor a method which breaks "The law of Demeter" principle?

  - by dreza

  I often find myself breaking this principle (not intentially, just through bad design). However recently I've seen a bit of code that I'm not sure of the best approach. I have a number of classes. For simplicity I've taken out the bulk of the classes methods etc public class Paddock { public SoilType Soil { get; private set; } // a whole bunch of other properties around paddock information } public class SoilType { public SoilDrainageType Drainage { get; private set; } // a whole bunch of other properties around soil types } public class SoilDrainageType { // a whole bunch of public properties that expose soil drainage values public double GetProportionOfDrainage(SoilType soil, double blockRatio) { // This method does a number of calculations using public properties // exposed off SoilType as well as the blockRatio value in some conditions } } In the code I have seen in a number of places calls like so paddock.Soil.Drainage.GetProportionOfDrainage(paddock.Soil, paddock.GetBlockRatio()); or within the block object itself in places it's Soil.Drainage.GetProportionOfDrainage(this.Soil, this.GetBlockRatio()); Upon reading this seems to break "The Law of Demeter" in that I'm chaining together these properties to access the method I want. So my thought in order to adjust this was to create public methods on SoilType and Paddock that contains wrappers i.e. on paddock it would be public class Paddock { public double GetProportionOfDrainage() { return Soil.GetProportionOfDrainage(this.GetBlockRatio()); } } on the SoilType it would be public class SoilType { public double GetProportionOfDrainage(double blockRatio) { return Drainage.GetProportionOfDrainage(this, blockRatio); } } so now calls where it used would be simply // used outside of paddock class where we can access instances of Paddock paddock.GetProportionofDrainage() or this.GetProportionOfDrainage(); // if used within Paddock class This seemed like a nice alternative. However now I have a concern over how would I enforce this usage and stop anyone else from writing code such as paddock.Soil.Drainage.GetProportionOfDrainage(paddock.Soil, paddock.GetBlockRatio()); rather than just paddock.GetProportionOfDrainage(); I need the properties to remain public at this stage as they are too ingrained in usage throughout the code block. However I don't really want a mixture of accessing the method on DrainageType directly as that seems to defeat the purpose altogether. What would be the appropiate design approach in this situation? I can provide more information as required to better help in answers. Is my thoughts on refactoring this even appropiate or should is it best to leave it as is and use the property chaining to access the method as and when required?

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• Unknown C# keywords: params

  - by Chris Skardon

  Often overlooked, and (some may say) unloved, is the params keyword, but it’s an awesome keyword, and one you should definitely check out. What does it do? Well, it lets you specify a single parameter that can have a variable number of arguments. You what? Best shown with an example, let’s say we write an add method: public int Add(int first, int second) { return first + second; } meh, it’s alright, does what it says on the tin, but it’s not exactly awe-inspiring… Oh noes! You need to add 3 things together??? public int Add(int first, int second, int third) { return first + second + third; } oh yes, you code master you! Overloading a-plenty! Now a fourth… Ok, this is starting to get a bit ridiculous, if only there was some way… public int Add(int first, int second, params int[] others) { return first + second + others.Sum(); } So now I can call this with any number of int arguments? – well, any number > 2..? Yes! int ret = Add(1, 2, 3); Is as valid as: int ret = Add(1, 2, 3, 4); Of course you probably won’t really need to ever do that method, so what could you use it for? How about adding strings together? What about a logging method? We all know ToString can be an expensive method to call, it might traverse every node on a class hierarchy, or may just be the name of the type… either way, we don’t really want to call it if we can avoid it, so how about a logging method like so: public void Log(LogLevel level, params object[] objs) { if(LoggingLevel < level) return; StringBuilder output = new StringBuilder(); foreach(var obj in objs) output.Append((obj == null) ? "null" : obj.ToString()); return output; } Now we only call ‘ToString’ when we want to, and because we’re passing in just objects we don’t have to call ToString if the Logging Level isn’t what we want… Of course, there are a multitude of things to use params for…

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