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• Information Spilling Across Object Boundaries

  - by Winston Ewert

  Many times my business objects tend to have situations where information needs to cross object boundaries too often. When doing OO, we want information to be in one object and as much as possible all code dealing with that information should be in that object. However, business rules do not follow this principle giving me trouble. As an example suppose that we have an Order which has a number of OrderItems which refers to an InventoryItem which has a price. I invoke Order.GetTotal() which sums the result of OrderItem.GetPrice() which multiples a quantity by InventoryItem.GetPrice(). So far so good. But then we find out that some items are sold with a two for one deal. We can handle this by having OrderItem.GetPrice() do something like InventoryItem.GetPrice( quantity ) and letting InventoryItem deal with this. However, then we find out that the two-for-one deal only lasts for a particular time period. This time period needs to be based on the date of the order. Now we change OrderItem.GetPrice() to be InventoryItem.GetPrice( quatity, order.GetDate() ) But then we need to support different prices depending on how long the customer has been in the system: InventoryItem.GetPrice( quantity, order.GetDate(), order.GetCustomer() ) But then it turns out that the two-for-one deals apply not just to buying multiple of the same inventory item but multiple for any item in a InventoryCategory. At this point we throw up our hands and just give the InventoryItem the order item and allow it to travel over the object reference graph via accessors to get the information its needs: InventoryItem.GetPrice( this ) TL;DR I want to have coupling in objects, but business rules often force me to access information from all over the place in order to make particular decisions. Are there good techniques for dealing with this? Do others find the same problem?

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• Detecting collision between ball (circle) and brick(rectangle)?

  - by James Harrison

  Ok so this is for a small uni project. My lecturer provided me with a framework for a simple brickbreaker game. I am currently trying to overcome to problem of detecting a collision between the two game objects. One object is always the ball and the other objects can either be the bricks or the bat. public Collision hitBy( GameObject obj ) { //obj is the bat or the bricks //the current object is the ball // if ball hits top of object if(topX + width >= obj.topX && topX <= obj.topX + obj.width && topY + height >= obj.topY - 2 && topY + height <= obj.topY){ return Collision.HITY; } //if ball hits left hand side else if(topY + height >= obj.topY && topY <= obj.topY + obj.height && topX + width >= obj.topX -2 && topX + width <= obj.topX){ return Collision.HITX; } else return Collision.NO_HIT; } So far I have a method that is used to detect this collision. The the current obj is a ball and the obj passed into the method is the the bricks. At the moment I have only added statement to check for left and top collisions but do not want to continue as I have a few problems. The ball reacts perfectly if it hits the top of the bricks or bat but when it hits the ball often does not change directing. It seems that it is happening toward the top of the left hand edge but I cannot figure out why. I would like to know if there is another way of approaching this or if people know where I'm going wrong. Lastly the collision.HITX calls another method later on the changes the x direction likewise with y.

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• Low-level game engine renderer design

  - by Mark Ingram

  I'm piecing together the beginnings of an extremely basic engine which will let me draw arbitrary objects (SceneObject). I've got to the point where I'm creating a few sensible sounding classes, but as this is my first outing into game engines, I've got the feeling I'm overlooking things. I'm familiar with compartmentalising larger portions of the code so that individual sub-systems don't overly interact with each other, but I'm thinking more of the low-level stuff, starting from vertices working up. So if I have a Vertex class, I can combine that with a list of indices to make a Mesh class. How does the engine determine identical meshes for objects? Or is that left to the level designer? Once we have a Mesh, that can be contained in the SceneObject class. And a list of SceneObject can be placed into the Scene to be drawn. Right now I'm only using OpenGL, but I'm aware that I don't want to be tying OpenGL calls right in to base classes (such as updating the vertices in the Mesh, I don't want to be calling glBufferData etc). Are there any good resources that discuss these issues? Are there any "common" heirachies which should be used?

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• What causes player box/world geometry glitches in old games?

  - by Alexander

  I'm looking to understand and find the terminology for what causes - or allows - players to interfere with geometry in old games. Famously, ID's Quake3 gave birth to a whole community of people breaking the physics by jumping, sliding, getting stuck and launching themselves off points in geometry. Some months ago (though I'd be darned if I can find it again!) I saw a conference held by Bungie's Vic DeLeon and a colleague in which Vic briefly discussed the issues he ran into while attempting to wrap 'collision' objects (please correct my terminology) around environment objects so that players could appear as though they were walking on organic surfaces, while not clipping through them or appear to be walking on air at certain points, due to complexities in the modeling. My aim is to compose a case study essay for University in which I can tackle this issue in games, drawing on early exploits and how techniques have changed to address such exploits and to aid in the gameplay itself. I have 3 current day example of where exploits still exist, however specifically targeting ID Software clearly shows they've massively improved their techniques between Q3 and Q4. So in summary, with your help please, I'd like to gain a slightly better understanding of this issue as a whole (its terminology mainly) so I can use terms and ask the right questions within the right contexts. In practical application, I know what it is, I know how to do it, but I don't have the benefit of level design knowledge yet and its technical widgety knick-knack terms =) Many thanks in advance AJ

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• Scene graphs and spatial partitioning structures: What do you really need?

  - by tapirath

  I've been fiddling with 2D games for awhile and I'm trying to go into 3D game development. I thought I should get my basics right first. From what I read scene graphs hold your game objects/entities and their relation to each other like 'a tire' would be the child of 'a vehicle'. It's mainly used for frustum/occlusion culling and minimizing the collision checks between the objects. Spatial partitioning structures on the other hand are used to divide a big game object (like the map) to smaller parts so that you can gain performance by only drawing the relevant polygons and again minimizing the collision checks to those polygons only. Also a spatial partitioning data structure can be used as a node in a scene graph. But... I've been reading about both subjects and I've seen a lot of "scene graphs are useless" and "BSP performance gain is irrelevant with modern hardware" kind of articles. Also some of the game engines I've checked like gameplay3d and jmonkeyengine are only using a scene graph (That also may be because they don't want to limit the developers). Whereas games like Quake and Half-Life only use spatial partitioning. I'm aware that the usage of these structures very much depend on the type of the game you're developing so for the sake of clarity let's assume the game is a FPS like Counter-Strike with some better outdoor environment capabilities (like a terrain). The obvious question is which one is needed and why (considering the modern hardware capabilities). Thank you.

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• How do I implement movement in a WPF Adventure game?

  - by ZeroPhase

  I'm working on making a short WPF adventure game. The only major hurdle I have right now is how to animate objects on the screen correctly. I've experimented with DoubleAnimation and ThicknessAnimation both enable movement of the character, but the speed is a bit erratic. The objects I'm trying to move around are labels in a grid, I'm checking the mouse's position in terms of the canvas I have the grid in. Does anyone have any suggestions for coding the movement, while still allowing mouse clicks to pick up items when needed? It would be nice if I could continue using the Visual Studio GUI Editor. By the way, I'm fine with scrapping labels in a grid for a more ideal object to manipulate. Here's my movement code: ThicknessAnimation ta = new ThicknessAnimation(); The event handling movement: private void Hansel_MouseLeftButtonDown(object sender, MouseButtonEventArgs e) { ta.FillBehavior = FillBehavior.HoldEnd; ta.From = Hansel.Margin; double newX = Mouse.GetPosition(PlayArea).X; double newY = Mouse.GetPosition(PlayArea).Y; if (newX < Convert.ToDouble(Hansel.Margin.Left)) { //newX = -1 * newX; ta.To = new Thickness(0, newY, newX, 0); } else if (newY < Convert.ToDouble(Hansel.Margin.Top)) { newY = -1 * newY; } else { ta.To = new Thickness(newX, newY, 0, 0); } ta.Duration = new Duration(TimeSpan.FromSeconds(2)); Hansel.BeginAnimation(Grid.MarginProperty, ta); } ScreenShot with annotations: http://i1118.photobucket.com/albums/k608/sealclubberr/clickToMove_zps9d4a33cc.png ScreenShot with example movement: http://i1118.photobucket.com/albums/k608/sealclubberr/clickToMove_zps51f2359f.jpg

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• Organizing MVC entities communication

  - by Stefano Borini

  I have the following situation. Imagine you have a MainWindow object who is layouting two different widgets, ListWidget and DisplayWidget. ListWidget is populated with data from the disk. DisplayWidget shows the details of the selection the user performs in the ListWidget. I am planning to do the following: in MainWindow I have the following objects: ListWidget ListView ListModel ListController ListView is initialized passing the ListWidget. ListViewController is initialized passing the View and the Model. Same happens for the DisplayWidget: DisplayWidget DisplayView DisplayModel DisplayController I initialize the DisplayView with the widget, and initialize the Model with the ListController. I do this because the DisplayModel wraps the ListController to get the information about the current selection, and the data to be displayed in the DisplayView. I am very rusty with MVC, being out of UI programming since a while. Is this the expected interaction layout for having different MVC triplets communicate ? In other words, MVC focus on the interaction of three objects. How do you put this interaction as a whole into a larger context of communication with other similar entities, MVC or not ?

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• Does immutability entirely eliminate the need for locks in multi-processor programming?

  - by GlenPeterson

  Part 1 Clearly Immutability minimizes the need for locks in multi-processor programming, but does it eliminate that need, or are there instances where immutability alone is not enough? It seems to me that you can only defer processing and encapsulate state so long before most programs have to actually DO something. If a program performs actions on multiple processors, something needs to collect and aggregate the results. All this involves multi-process communication before, after, and possibly during some transformations. The start and end state of the machines are different. Can this always be done with no locks just by throwing out each object and creating a new one instead of changing the original (a crude view of immutability)? What cases still require locking? I'm interested in both the theoretical/academic answer and the practical/real-world answer. I know a lot of functional programmers like to talk about "no side effect" but in the "real world" everything has a side effect. Every processor click takes time and electricity and machine resources away from other processes. So I understand that there may be more than one perspective to answer this question from. If immutability is safe, given certain bounds or assumptions, I want to know what the borders of the "safety zone" are exactly. Some examples of possible boundaries: I/O Exceptions/errors Interfaces with programs written in other languages Interfaces with other machines (physical, virtual, or theoretical) Special thanks to @JimmaHoffa for his comment which started this question! Part 2 Multi-processor programming is often used as an optimization technique - to make some code run faster. When is it faster to use locks vs. immutable objects? Given the limits set out in Amdahl's Law, when can you achieve better over-all performance (with or without the garbage collector taken into account) with immutable objects vs. locking mutable ones? Summary I'm combining these two questions into one to try to get at where the bounding box is for Immutability as a solution to threading problems.

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• Strange and erratic transformations when using OpenGL VBOs to render scene

  - by janoside

  I have an existing iOS game with fairly simple scenes (all textured quads) and I'm using Apple's "Texture2D" class. I'm trying to convert this class to use VBOs since the vertices of my objects basically never change so I may as well not re-create them for every object every frame. I have the scene rendering using VBOs but the sizes and orientations of all rendered objects are strange and erratic - though locations seem generally correct. I've been toying with this code for a few days now, and I've found something odd: if I re-create all of my VBOs each frame, everything looks correct, even though I'm almost certain my vertices are not changing. Other notes I'm basing my work on this tutorial, and therefore am also using "IBOs" I create my buffers before rendering begins My buffers include vertex and texture data I'm using OpenGL ES 1.1 Fearing some strange effect of the current matrix GL state at the time of buffer creation I've also tried wrapping my buffer-setup code in a "pushMatrix-loadIdentity-popMatrix" block which (as expected) had no effect I'm aware that various articles have been published demonstrating that VBOs may not help performance, but I want to understand this problem and at least have the option to use them. I realize this is a shot in the dark, but has anyone else experienced this type of strange behavior? What might I be doing to result in this behavior? It's rather difficult for me to isolate the problem since I'm working in an existing, moderately complex project, so suggestions about how to approach the problem are also quite welcome.

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• Understanding Box2d Restitution & Bouncing

  - by layzrr

  I'm currently trying to implement basketball bouncing into my game using Box2d (jBox2d technically), but I'm a bit confused about restitution. While trying to create the ball in the testbed first, I've run into infinite bouncing, as described in this question, however obviously not using my own implementation. The Box2d manual describes restitution as follows: Restitution is used to make objects bounce. The restitution value is usually set to be between 0 and 1. Consider dropping a ball on a table. A value of zero means the ball won't bounce. This is called an inelastic collision. A value of one means the ball's velocity will be exactly reflected. This is called a perfectly elastic collision. My confusion lies in that I am still getting infinite bouncing with restitution values at 0.75/0.8. The same behavior can be seen in the testbed under Collision Watching - Varying Restitution, on the 6th and 7th balls. I believe the last one has restitution of 1, which makes sense, but I don't understand why the second to last ball bounces infinitely (as is happening with my working basketball I've created). I am looking to understand the restitution concept more fully, as well as look for a solution to infinite bouncing with the Box2d framework. My instinct was to sleep objects that appeared to be moving in very small increments, but this seems like a misuse of the engine. Should I just work with lower restitution values altogether?

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• Why do memory-managed languages retain the `new` keyword?

  - by Channel72

  The new keyword in languages like Java, Javascript, and C# creates a new instance of a class. This syntax seems to have been inherited from C++, where new is used specifically to allocate a new instance of a class on the heap, and return a pointer to the new instance. In C++, this is not the only way to construct an object. You can also construct an object on the stack, without using new - and in fact, this way of constructing objects is much more common in C++. So, coming from a C++ background, the new keyword in languages like Java, Javascript, and C# seemed natural and obvious to me. Then I started to learn Python, which doesn't have the new keyword. In Python, an instance is constructed simply by calling the constructor, like: f = Foo() At first, this seemed a bit off to me, until it occurred to me that there's no reason for Python to have new, because everything is an object so there's no need to disambiguate between various constructor syntaxes. But then I thought - what's really the point of new in Java? Why should we say Object o = new Object();? Why not just Object o = Object();? In C++ there's definitely a need for new, since we need to distinguish between allocating on the heap and allocating on the stack, but in Java all objects are constructed on the heap, so why even have the new keyword? The same question could be asked for Javascript. In C#, which I'm much less familiar with, I think new may have some purpose in terms of distinguishing between object types and value types, but I'm not sure. Regardless, it seems to me that many languages which came after C++ simply "inherited" the new keyword - without really needing it. It's almost like a vestigial keyword. We don't seem to need it for any reason, and yet it's there. Question: Am I correct about this? Or is there some compelling reason that new needs to be in C++-inspired memory-managed languages like Java, Javascript and C#?

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• Japanese Multiplication simulation - is a program actually capable of improving calculation speed?

  - by jt0dd

  On SuperUser, I asked a (possibly silly) question about processors using mathematical shortcuts and would like to have a look at the possibility at the software application of that concept. I'd like to write a simulation of Japanese Multiplication to get benchmarks on large calculations utilizing the shortcut vs traditional CPU multiplication. I'm curious as to whether it makes sense to try this. My Question: I'd like to know whether or not a software math shortcut, as described above is actually a shortcut at all. This is a question of programming concept. By utilizing the simulation of Japanese Multiplication, is a program actually capable of improving calculation speed? Or am I doomed from the start? The answer to this question isn't required to determine whether or not the experiment will succeed, but rather whether or not it's logically possible for such a thing to occur in any program, using this concept as an example. My theory is that since addition is computed faster than multiplication, a simulation of Japanese multiplication may actually allow a program to multiply (large) numbers faster than the CPU arithmetic unit can. I think this would be a very interesting finding, if it proves to be true. If, in the multiplication of numbers of any immense size, the shortcut were to calculate the result via less instructions (or faster) than traditional ALU multiplication, I would consider the experiment a success.

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• An alternative to multiple inheritance when creating an abstraction layer?

  - by sebf

  In my project I am creating an abstraction layer for some APIs. The purpose of the layer is to make multi-platform easier, and also to simplify the APIs to the feature set that I need while also providing some functionality, the implementation of which will be unique to each platform. At the moment, I have implemented it by defining and abstract class, which has methods which creates objects that implement interfaces. The abstract class and these interfaces define the capabilities of my abstraction layer. The implementation of these in my layer should of course be arbitrary from the POV view of my application, but I have done it, for my first API, by creating chains of subclasses which add more specific functionality as the features of the APIs they expose become less generic. An example would probably demonstrate this better: //The interface as seen by the application interface IGenericResource { byte[] GetSomeData(); } interface ISpecificResourceOne : IGenericResource { int SomePropertyOfResourceOne {get;} } interface ISpecificResourceTwo : IGenericResource { string SomePropertyOfResourceTwo {get;} } public abstract class MyLayer { ISpecificResourceOne CreateResourceOne(); ISpecificResourceTwo CreateResourceTwo(); void UseResourceOne(ISpecificResourceOne one); void UseResourceTwo(ISpecificResourceTwo two); } //The layer as created in my library public class LowLevelResource : IGenericResource { byte[] GetSomeData() {} } public class ResourceOne : LowLevelResource, ISpecificResourceOne { int SomePropertyOfResourceOne {get{}} } public class ResourceTwo : ResourceOne, ISpecificResourceTwo { string SomePropertyOfResourceTwo {get {}} } public partial class Implementation : MyLayer { override UseResourceOne(ISpecificResourceOne one) { DoStuff((ResourceOne)one); } } As can be seen, I am essentially trying to have two inheritance chains on the same object, but of course I can't do this so I simulate the second version with interfaces. The thing is though, I don't like using interfaces for this; it seems wrong, in my mind an interface defines a contract, any class that implements that interface should be able to be used where that interface is used but here that is clearly not the case because the interfaces are being used to allow an object from the layer to masquerade as something else, without the application needing to have access to its definition. What technique would allow me to define a comprehensive, intuitive collection of objects for an abstraction layer, while their implementation remains independent? (Language is C#)

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• XNA 4.0, Combining model draw calls

  - by MayContainNuts

  I have the following problem: The levels in my game are made up of a Large Quantity of small Models and because of that I am experiencing frame rate problems. I already did some research and came to the conclusion that the amount of draw calls I am making must be the root of my problems. I've looked around for a while now and couldn't quite find a satisfying solution. I can't cull any of those models, in a worst case scenario there could be 1000 of them visible at the same time. I also looked at Hardware geometry Instancing, but I don't think that's quite what I'm looking for, because the level consists of a lot of different parts. So, what I'd like to do is combining 100 or 200 of these Models into a single large one and draw it as a whole 'chunk'. The whole geometry is static so it wouldn't have to be changed after combining, but different parts of it would have to use different textures (I think I can accomplish that with a texture atlas). But I have no idea how to to that, so does anybody have any suggestions?

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• Should you create a class within a method?

  - by Amndeep7

  I have made a program using Java that is an implementation of this project: http://nifty.stanford.edu/2009/stone-random-art/sml/index.html. Essentially, you create a mathematical expression and, using the pixel coordinate as input, make a picture. After I initially implemented this in serial, I then implemented it in parallel due to the fact that if the picture size is too large or if the mathematical expression is too complex (especially considering the fact that I made the expression recursively), it takes a really long time. During this process, I realized that I needed two classes which implemented the Runnable interface as I had to put in parameters for the run method, which you aren't allowed to do directly. One of these classes ended up being a medium sized static inner class (not large enough to make an independent class file for it though). The other though, just needed a few parameters to determine some indexes and the size of the for loop that I was making run in parallel - here it is: class DataConversionRunnable implements Runnable { int jj, kk, w; DataConversionRunnable(int column, int matrix, int wid) { jj = column; kk = matrix; w = wid; } public void run() { for(int i = 0; i < w; i++) colorvals[kk][jj][i] = (int) ((raw[kk][jj][i] + 1.0) * 255 / 2.0); increaseCounter(); } } My question is should I make it a static inner class or can I just create it in a method? What is the general programming convention followed in this case?

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• cocos2d/OpenGL multitexturing problem

  - by Gajoo

  I've got a simple shader to test multitextureing the problem is both samplers are using same image as their reference. the shader code is basically just this : vec4 mid = texture2D(u_texture,v_texCoord); float g = texture2D(u_guide,v_guideCoord); gl_FragColor = vec4(g , mid.g,0,1); and this is how I'm calling draw function : int last_State; glGetIntegerv(GL_ACTIVE_TEXTURE, &last_State); glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_2D, getTexture()->getName()); glActiveTexture(GL_TEXTURE1); glEnable(GL_TEXTURE_2D); glBindTexture(GL_TEXTURE_2D, mGuideTexture->getName()); ccGLEnableVertexAttribs( kCCVertexAttribFlag_TexCoords |kCCVertexAttribFlag_Position); glVertexAttribPointer(kCCVertexAttrib_Position, 2, GL_FLOAT, GL_FALSE, 0, vertices); glVertexAttribPointer(kCCVertexAttrib_TexCoords, 2, GL_FLOAT, GL_FALSE, 0, texCoord); glDrawArrays(GL_TRIANGLE_STRIP, 0, 4); glDisable(GL_TEXTURE_2D); I've already check mGuideTexture->getName() and getTexture()->getName() are returning correct textures. but looking at the result I can tell, both samplers are reading from getTexture()->getName(). here are some screen shots showing what is happening : The image rendered Using above codes The image rendered when I change textures passed to samples I'm expecting to see green objects from the first picture with red objects hanging from the top.

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• One Step-Ahead A-Star

  - by Jonathan Dickinson

  I am attempting to create a server-centric RTS (as opposed to usual parallel synchronised simulation route of most RTS games today) - however I am still leveraging the discreet N-turns-ahead paradigm discussed by one of the AOE developers on Gamasutra. I have [possibly questionably?] decided that the path finding should only ever find the next cell the entity needs to move to, and was wondering if anyone has any clever ideas on how to optimize the algorithm for this specific scenario - or any other ideas on how to keep the pathfinding as lean as possible on the server. I have investigated a few possible algorithms but could only come up with one appropriation: Tiered A-Star - Relatively large T1 tiles, work out (and cache) each cell as you enter it. Other than that: doing the full A-Star pass and caching the entire path, which might use too much memory if a large amount of units are present. I know about the existence of naive progressive pathfinding algorithms (if you hit a block, turn in the direction closer to your target etc.) but they suffer from infinite feedback loops - and very poor pathing even if visited blocks are memorised. Not an option. Many thanks.

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• Burg Custom Icons work only with specific themes

  - by el10780

  I have made a custom icon for burg loader for my Lenovo Recovery Partition.I have made 3 icons : large_qdrive.png (128 X 128 pixels) small_qdrive.png (24 X 24 pixels) grey_qdrive.png (128 x 128 pixels) The .png icons that I created I made them using gimp from a qdrive.ico file that I found in the Lenovo Recovery Partition. I transferred the icons to the /boot/burg/themes/icons folder and I added to the class list of the grey,large,small and the hover files the following lines : -qdrive { image = "$$/large_qdrive.png" } in the large file -qdrive { image = "$$/small_qdrive.png" } in the small file -qdrive { image = "$$/grey_qdrive.png" } in the grey file -qdrive { image = "$$/grey_qdrive.png:$$/large_qdrive.png" } in the hover file I ran sudo update-burg and after that I modified the following line in the burg.cfg file : menuentry "Windows 7 (loader) (on /dev/sda2)" --class windows --class os { to menuentry "Windows 7 (loader) (on /dev/sda2)" --class qdrive --class os { and I also tried to change the title for the Lenovo Recovery Partition,so I tried this as well: menuentry "Lenovo Recovery Partition (on /dev/sda2)" --class qdrive --class os { None of this tries enforced actually burg loader to use the custom icon that I made and I can't figure out why. I have to mention also that there are a few themes that I have installed in burg which actually are able to use the small_qdrive.png icon that I made,but all the others which use either the large_qdrive.png or the grey_qdrive.png weren't able to use the custom icons. I have double checked for typos in all the files that I have created or I modified,so I am pretty sure that I haven't misspelled anything. I have checked also the title of the custom icons that I made and neither of them have a typo. I have looked also if there are any other folder that the themes might use to retrieve the icons,but it seems that all of them except for **Fortune** theme,which I downloaded from OMG!UBUNTU,use the icons folder which is located in /boot/burg/themes/icons I tried to add the custom icons to the icons folder of the theme **Fortune**,but still nothing happened.

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• Composing programs from small simple pieces: OOP vs Functional Programming

  - by Jay Godse

  I started programming when imperative programming languages such as C were virtually the only game in town for paid gigs. I'm not a computer scientist by training so I was only exposed to Assembler and Pascal in school, and not Lisp or Prolog. Over the 1990s, Object-Oriented Programming (OOP) became more popular because one of the marketing memes for OOP was that complex programs could be composed of loosely coupled but well-defined, well-tested, cohesive, and reusable classes and objects. And in many cases that is quite true. Once I learned object-oriented programming my C programs became better because I structured them more like classes and objects. In the last few years (2008-2014) I have programmed in Ruby, an OOP language. However, Ruby has many functional programming (FP) features such as lambdas and procs, which enable a different style of programming using recursion, currying, lazy evaluation and the like. (Through ignorance I am at a loss to explain why these techniques are so great). Very recently, I have written code to use methods from the Ruby Enumerable library, such as map(), reduce(), and select(). Apparently this is a functional style of programming. I have found that using these methods significantly reduce code volume, and make my code easier to debug. Upon reading more about FP, one of the marketing claims made by advocates is that FP enables developers to compose programs out of small well-defined, well-tested, and reusable functions, which leads to less buggy code, and low code volume. QUESTIONS: Is the composition of complex program by using FP techniques contradictory to or complementary to composition of a complex program by using OOP techniques? In which situations is OOP more effective, and when is FP more effective? Is it possible to use both techniques in the same complex program? Do the techniques overlap or contradict each other?

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• Oracle Identity Manager ADF Customization

  - by Arda Eralp

  This blog entry includes an example about customization Oracle Identity Manager (OIM) Self Service screen. Before customization all users that can be logged in OIM Self Service can see "Administration" tab on left menu. On this example we create "Managers" role and only users that have managers role can see "Administration" tab. Step 1: Create "Manager" role  Step 2: Create Sandbox  Step 3: Customize ADF Select "Customize" on the top menu Select "Source" instead of "Design" on top  Select "Administration" tab with blue rectangle and edit component Edit "visible" with expression builder #{oimcontext.currentUser.roles['Manager'] != null} Apply Step 4: Apply to All and Publish sandbox Notes:  This table objects can use for expression. Objects Description #{oimcontext.currentUser['ATTRIBUTE_NAME']} #{oimcontext.currentUser['UDF_NAME']} #{oimcontext.currentUser.roles} #{oimcontext.currentUser.roles['SYSTEM ADMINISTRATORS'] != null} Boolean #{oimcontext.currentUser.adminRoles['OrclOIMSystemAdministrator'] != null} Boolean

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• Empty interface to combine multiple interfaces

  - by user1109519

  Suppose you have two interfaces: interface Readable { public void read(); } interface Writable { public void write(); } In some cases the implementing objects can only support one of these but in a lot of cases the implementations will support both interfaces. The people who use the interfaces will have to do something like: // can't write to it without explicit casting Readable myObject = new MyObject(); // can't read from it without explicit casting Writable myObject = new MyObject(); // tight coupling to actual implementation MyObject myObject = new MyObject(); None of these options is terribly convenient, even more so when considering that you want this as a method parameter. One solution would be to declare a wrapping interface: interface TheWholeShabam extends Readable, Writable {} But this has one specific problem: all implementations that support both Readable and Writable have to implement TheWholeShabam if they want to be compatible with people using the interface. Even though it offers nothing apart from the guaranteed presence of both interfaces. Is there a clean solution to this problem or should I go for the wrapper interface? UPDATE It is in fact often necessary to have an object that is both readable and writable so simply seperating the concerns in the arguments is not always a clean solution. UPDATE2 (extracted as answer so it's easier to comment on) UPDATE3 Please beware that the primary usecase for this is not streams (although they too must be supported). Streams make a very specific distinction between input and output and there is a clear separation of responsibilities. Rather, think of something like a bytebuffer where you need one object you can write to and read from, one object that has a very specific state attached to it. These objects exist because they are very useful for some things like asynchronous I/O, encodings,...

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• Adding 2D vector movement with rotation applied

  - by Michael Zehnich

  I am trying to apply a slight sine wave movement to objects that float around the screen to make them a little more interesting. I would like to apply this to the objects so that they oscillate from side to side, not front to back (so the oscillation does not affect their forward velocity). After reading various threads and tutorials, I have come to the conclusion that I need to create and add vectors, but I simply cannot come up with a solution that works. This is where I'm at right now, in the object's update method (updated based on comments): Vector2 oldPosition = new Vector2(spritePos.X, spritePos.Y); //note: newPosition is initially set in the constructor to spritePos.x/y Vector2 direction = newPosition - oldPosition; Vector2 perpendicular = new Vector2(direction.Y, -direction.X); perpendicular.Normalize(); sinePosAng += 0.1f; perpendicular.X += 2.5f * (float)Math.Sin(sinePosAng); spritePos.X += velocity * (float)Math.Cos(radians); spritePos.Y += velocity * (float)Math.Sin(radians); spritePos += perpendicular; newPosition = spritePos;

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• 2D Side scroller collision detection

  - by Shanon Simmonds

  I am trying to do some collision detection between objects and tiles, but the tiles do not have there own x and y position, they are just rendered to the x and y position given, there is an array of integers which has the ids of the tiles to use(which are given from an image and all the different colors are assigned different tiles) int x0 = camera.x / 16; int y0 = camera.y / 16; int x1 = (camera.x + screen.width) / 16; int y1 = (camera.y + screen.height) / 16; for(int y = y0; y < y1; y++) { if(y < 0 || y >= height) continue; // height is the height of the level for(int x = x0; x < x1; x++) { if(x < 0 || x >= width) continue; // width is the width of the level getTile(x, y).render(screen, x * 16, y * 16); } } I tried using the levels getTile method to see if the tile that the object was going to advance to, to see if it was a certain tile, but, it seems to only work in some directions. Any ideas on what I'm doing wrong and fixes would be greatly appreciated. What's wrong is that it doesn't collide properly in every direction and also this is how I tested for a collision in the objects class if(!level.getTile((x + xa) / 16, (y + ya) / 16).isSolid()) { x += xa; y += ya; } EDIT: xa and ya represent the direction as well as the movement, if xa is negative it means the object is moving left, if its positive it is moving right, and same with ya except negative for up, positive for down.

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• How can I discourage the use of Access?

  - by Greg Buehler

  Lets pretend that a very large company (revenue numbers with more than 8 figures) is looking to do a refresh on a software system, particularly the dashboard used by employees. This system was originally put together in the early 1990's to handle inventory tracking and storage across a variety of facilities (10+). Since this large company is now in the process of implementing some of these inventory processes with SAP they are in need of a major refresh. The existing system: Microsoft Access project performs dashboard duties Unique shipping/receiving configurations at different facilities require unique forms and queries within the Access project Uses 3rd party libraries referenced by Access to directly interface with at control system (read: motors, conveyors, and counters) Individual SQL Server 2000 instances (some traces of pre-update SQL Server 6.0 documents) at each facility The Issue: This system started as a home brewed inventory tracking scheme with a single internal sponsor who is still in charge of the technical direction. The original sponsor prescribing the desired deliverables that are being called for in the current RFP. The RFP describes a system based around a single Access project. Any suggestion that Access is ill suited for a project of this scope are shot down under the reasoning that "it works for the scope now". Are there any case studies, notices, or statements that can be used to disuade this potential customer from repeating their mistake? Does Microsoft make any statements directly about when it is highly recommended to ditch Access?

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• How should I structure my database to gain maximum efficiently in this scenario?

  - by Bob Jansen

  I'm developing a PHP script that analyzes the web traffic of my clients websites. By placing a link to a javascript on the clients website (think of Google Analyses), my script harvests information like: the visitors IP address, reference link, current page link, user agent, etc. Now my clients can view these statistics via a control panel that I have build. These clients can also adjust profile settings, set firewall rules, create support tickets and pay invoices. Currently all the the traffic is stored in one table. You can imagine that this tabel would become very large as some my clients receive thousands of pageviews per day. Furthermore, all the traffic data of each client would be stored in the same table, creating a mess. This is the same for the firewall rules currently, and the invoice and support system. I'm looking for way to structure my database in a more organized way to hold large amounts of data of multiple users. This is the first project that I'm developing that deals with so much data, and would like to hear suggestions and tips. I was thinking of using multiple databases to structure the data. The main database will store users data (email,pass,id,etc) admin/website settings. Than each client will have an unique database labeled prefix_userid, which carry tables holding their traffic, invoice, and support ticket data. Would this be a solution, and would it slow down or speed up overall performances (that is spreading the data over muliple databases). I have a solid VPS, but would like to safe and be as effient as possible.

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