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• How does Starcraft 2 load it's metadata?

  - by chobok

  Lets say you are playing Starcraft 2 melee map. The game loads the map. Melee maps have the following dependencies: Liberty (Mod) Liberty Multi (Mod) I think the game engine will load the data from Liberty (Mod) first, then from Liberty Multi (Mod). For data that exists in both dependencies, the engine will use the one from Liberty Multi (Mod). Is this correct? Liberty Multi (Mod) is updated with each patch of Starcraft 2. Does the game engine load just the latest version of Liberty Multi (Mod)? or Does the game engine load all the versions and overwrite duplicate data with the latest version?

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• What exactly can shaders be used for?

  - by Bane

  I'm not really a 3D person, and I've only used shaders a little in some Three.js examples, and so far I've got an impression that they are only being used for the graphical part of the equation. Although, the (quite cryptic) Wikipedia article and some other sources lead me to believe that they can be used for more than just graphical effects, ie, to program the GPU (Wikipedia). So, the GPU is still a processor, right? With a larger and a different instruction set for easier and faster vector manipulation, but still a processor. Can I use shaders to make regular programs (provided I've got access to the video memory, which is probable)? Edit: regular programs == "Applications", ie create windows/console programs, or at least have some way of drawing things on the screen, maybe even taking user input.

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• How AlphaBlend Blendstate works in XNA 4 when accumulighting light into a RenderTarget?

  - by cubrman

  I am using a Deferred Rendering engine from Catalin Zima's tutorial: His lighting shader returns the color of the light in the rgb channels and the specular component in the alpha channel. Here is how light gets accumulated: Game.GraphicsDevice.SetRenderTarget(LightRT); Game.GraphicsDevice.Clear(Color.Transparent); Game.GraphicsDevice.BlendState = BlendState.AlphaBlend; // Continuously draw 3d spheres with lighting pixel shader. ... Game.GraphicsDevice.BlendState = BlendState.Opaque; MSDN states that AlphaBlend field of the BlendState class uses the next formula for alphablending: (source × Blend.SourceAlpha) + (destination × Blend.InvSourceAlpha), where "source" is the color of the pixel returned by the shader and "destination" is the color of the pixel in the rendertarget. My question is why do my colors are accumulated correctly in the Light rendertarget even when the new pixels' alphas equal zero? As a quick sanity check I ran the following code in the light's pixel shader: float specularLight = 0; float4 light4 = attenuation * lightIntensity * float4(diffuseLight.rgb,specularLight); if (light4.a == 0) light4 = 0; return light4; This prevents lighting from getting accumulated and, subsequently, drawn on the screen. But when I do the following: float specularLight = 0; float4 light4 = attenuation * lightIntensity * float4(diffuseLight.rgb,specularLight); return light4; The light is accumulated and drawn exactly where it needs to be. What am I missing? According to the formula above: (source x 0) + (destination x 1) should equal destination, so the "LightRT" rendertarget must not change when I draw light spheres into it! It feels like the GPU is using the Additive blend instead: (source × Blend.One) + (destination × Blend.One)

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• Improving Click and Drag with C++

  - by Josh

  I'm currently using SFML 2.0 to develop a game in C++. I have a game sprite class that has a click and drag method. The method works, but there is a slight problem. If the mouse moves too fast, the object the user selected can't keep up and is left behind in the spot where the mouse left its bounds. I will share the class definition and the given function implementation. Definition: class codePeg { protected: FloatRect bounds; CircleShape circle; int xPos, yPos, xDiff, yDiff, once; int xBase, yBase; Vector2i mousePos; Vector2f circlePos; public: void init(RenderWindow& Window); void draw(RenderWindow& Window); void drag(RenderWindow& Window); void setPegPosition(int x, int y); void setPegColor(Color pegColor); void mouseOver(RenderWindow& Window); friend int isPegSelected(void); }; Implementation of the "drag" function: void codePeg::drag(RenderWindow& Window) { mousePos = Mouse::getPosition(Window); circlePos = circle.getPosition(); if(Mouse::isButtonPressed(Mouse::Left)) { if(mousePos.x > xPos && mousePos.y > yPos && mousePos.x - bounds.width < xPos && mousePos.y - bounds.height < yPos) { if(once) { xDiff = mousePos.x - circlePos.x; yDiff = mousePos.y - circlePos.y; once = 0; } xPos = mousePos.x - xDiff; yPos = mousePos.y - yDiff; circle.setPosition(xPos, yPos); } } else { once = 1; xPos = xBase; yPos = yBase; xDiff = 0; yDiff = 0; circle.setPosition(xBase, yBase); } Window.draw(circle); } Like I said, the function works, but to me, the code is very ugly and I think it could be improved and could be more efficient. The only thing I can think of as to why the object cannot keep up with the mouse is that there are too many function calls and/or checks. The user does not really have to mouse the mouse "fast" for it to happen, I would say at an average pace the object is left behind. How can I improve the code so that the object remains with the mouse when it is selected? Any help improving this code or giving advice is greatly appreciated.

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• How do I implement smooth movement in a Box2D platform game?

  - by Romeo

  I have implemented a character in JBox2D which moves with the help of a wheel rotating at the bottom of it. The movement is the best result I've had 'till now but it's a little glitchy when the character stands on the edge. So I am thinking should I use five smaller wheels instead of a big wheel. The wheel/wheels will not be visible in the finished product, now they are drawn for debugging. Here is a video. Is there a better way to do this using JBox2D?

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• How to handle multiple effect files in XNA

  - by Adam 'Pi' Burch

  So I'm using ModelMesh and it's built in Effects parameter to draw a mesh with some shaders I'm playing with. I have a simple GUI that lets me change these parameters to my heart's desire. My question is, how do I handle shaders that have unique parameters? For example, I want a 'shiny' parameter that affects shaders with Phong-type specular components, but for an environment mapping shader such a parameter doesn't make a lot of sense. How I have it right now is that every time I call the ModelMesh's Draw() function, I set all the Effect parameters as so foreach (ModelMesh m in model.Meshes) { if (isDrawBunny == true)//Slightly change the way the world matrix is calculated if using the bunny object, since it is not quite centered in object space { world = boneTransforms[m.ParentBone.Index] * Matrix.CreateScale(scale) * rotation * Matrix.CreateTranslation(position + bunnyPositionTransform); } else //If not rendering the bunny, draw normally { world = boneTransforms[m.ParentBone.Index] * Matrix.CreateScale(scale) * rotation * Matrix.CreateTranslation(position); } foreach (Effect e in m.Effects) { Matrix ViewProjection = camera.ViewMatrix * camera.ProjectionMatrix; e.Parameters["ViewProjection"].SetValue(ViewProjection); e.Parameters["World"].SetValue(world); e.Parameters["diffuseLightPosition"].SetValue(lightPositionW); e.Parameters["CameraPosition"].SetValue(camera.Position); e.Parameters["LightColor"].SetValue(lightColor); e.Parameters["MaterialColor"].SetValue(materialColor); e.Parameters["shininess"].SetValue(shininess); //e.Parameters //e.Parameters["normal"] } m.Draw(); Note the prescience of the example! The solutions I've thought of involve preloading all the shaders, and updating the unique parameters as needed. So my question is, is there a best practice I'm missing here? Is there a way to pull the parameters a given Effect needs from that Effect? Thank you all for your time!

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• How to remove seams from a tile map in 3D?

  - by Grimshaw

  I am using my OpenGL custom engine to render a tilemap made with Tiled, using a well spread tileset from the web. There is nothing fancy going on. I load the TMX file from Tiled and generate vertex arrays and index arrays to render the tilemap. I am rendering this tilemap as a wall in my 3D world, meaning that I move around with a fly camera in my 3D world and at Z=0 there is a plane showing me my tiles. Everything is working correctly but I get ugly seems between the tiles. I've tried orthographic and perspective cameras and with either I found particular sets of parameters for the projection and view matrices where the artifacts did not show, but otherwise they are there 99% of the time in multiple patterns, depending on the zoom and camera parameters like field of view. Here's a screenshot of the artifact being shown: http://i.imgur.com/HNV1g4M.png Here's the tileset I am using (which Tiled also uses and renders correctly): http://i.imgur.com/SjjHK4q.png My tileset has no mipmaps and is set to GL_NEAREST and GL_CLAMP_TO_EDGE values. I've looked around many articles in the internet and nothing helped. I tried uv correction so the uv fall at half of the texel, rather than the end of the texel to prevent interpolating with the neighbour value(which is transparency). I tried debugging with my geometry and I verified that with no texture and a random color in each tile, I don't seem to see any seams. All vertices have integer coordinates, i.e, the first tile is a quad from (0,0) to (1,1) and so on. Tried adding a little offset both to the UV and to the vertices to see if the gaps cease to exist. Disabled multisampling too. Nothing fixed it so far. Thanks.

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• Entity Component System for HUD and GUI

  - by Jason L.

  This is a very rough sketch of how I currently have things designed. It should, at least, give an idea of how my ECS is currently designed. If you notice in that diagram, I have basically split the HUD out of the ECS. They have their own set of things (HudLayer, HudComponent, etc) and are handled differently. This is where I'm struggling, though. There are many different instances in which the HUD will need to know about entities. Not just data changing (I have an event dispatcher for that), but the actual entity and all it encompasses. There are also situations where entities will need to be able to query the HUD for data. Let's take a couple examples: First, my equipment screen. On here I can change the equipment on a character (Entity). In order for this to happen, I need to know about the entity. At least I think I do? How can I handle this? The second scenario involves my Systems needing to query a HudComponent for data. A specific example would be my battle system. Each "team" is given a 3x3 grid they can move around in. See here: Skills target these cells, and not the player, so I would need a way for my systems to determine which cells are occupied and which are not. Basically I need a way for two way communication between Systems and my HUD. I know it's recommended (by some people, anyways) to take your HUD out of the ECS. Is that appropriate in my case?

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• Prevent oversteering catastrophe in racing games

  - by jdm

  When playing GTA III on Android I noticed something that has been annoying me in almost every racing game I've played (maybe except Mario Kart): Driving straight ahead is easy, but curves are really hard. When I switch lanes or pass somebody, the car starts swiveling back and forth, and any attempt to correct it makes it only worse. The only thing I can do is to hit the brakes. I think this is some kind of oversteering. What makes it so irritating is that it never happens to me in real life (thank god :-)), so 90% of the games with vehicles inside feel unreal to me (despite probably having really good physics engines). I've talked to a couple of people about this, and it seems either you 'get' racing games, or you don't. With a lot of practice, I did manage to get semi-good at some games (e.g. from the Need for Speed series), by driving very cautiously, braking a lot (and usually getting a cramp in my fingers). What can you do as a game developer to prevent the oversteering resonance catastrophe, and make driving feel right? (For a casual racing game, that doesn't strive for 100% realistic physics) I also wonder what games like Super Mario Kart exactly do differently so that they don't have so much oversteering? I guess one problem is that if you play with a keyboard or a touchscreen (but not wheels and pedals), you only have digital input: gas pressed or not, steering left/right or not, and it's much harder to steer appropriately for a given speed. The other thing is that you probably don't have a good sense of speed, and drive much faster than you would (safely) in reality. From the top of my head, one solution might be to vary the steering response with speed.

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• Flickering when accessing texture by offset

  - by TravisG

  I have this simple compute shader that basically just takes the input from one image and writes it to another. Both images are 128/128/128 in size and glDispatchCompute is called with (128/8,128/8,128/8). The source images are cleared to 0 before this compute shader is executed, so no undefined values should be floating around in there. (I have the appropriate memory barrier on the C++ side set before the 3D texture is accessed). This version works fine: #version 430 layout (location = 0, rgba16f) uniform image3D ping; layout (location = 1, rgba16f) uniform image3D pong; layout (local_size_x = 8, local_size_y = 8, local_size_z = 8) in; void main() { ivec3 sampleCoord = gl_GlobalInvocationID.xyz; imageStore(pong, imageLoad(ping,sampleCoord)); } Reading values from pong shows that it's just a copy, as intended. However, when I load data from ping with an offset: #version 430 layout (location = 0, rgba16f) uniform image3D ping; layout (location = 1, rgba16f) uniform image3D pong; layout (local_size_x = 8, local_size_y = 8, local_size_z = 8) in; void main() { ivec3 sampleCoord = gl_GlobalInvocationID.xyz; imageStore(pong, imageLoad(ping,sampleCoord+ivec3(1,0,0))); } The data that is written to pong seems to depend on the order of execution of the threads within the work groups, which makes no sense to me. When reading from the pong texture, visible flickering occurs in some spots on the texture. What am I doing wrong here?

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• Deformation of Sphere using Transformations

  - by Mert Toka

  I have a graphic related question. I need to have a transformation matrix that I have no idea about what it is. The problem is to create right image from the right sphere. I created those images in Maya, but I need some matrices for the graphics course. Here is the image: Our professor told us to use some sine and cosine in our transformations, but I have no idea what he meant. I thought of intersecting a plane from the grid(that is xz plane) and sphere, and then scaling down the resulting circle. Would that work? I also checked this paper, however it looks like a bit advanced for me. Another thing is I guess that paper is not about the same type of information I was looking for. It would be great if you could help me.

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• How to properly add texture to multi-fixture/shape b2Body

  - by Blazej Wdowikowski

  Hello to everyone this is my first poste here I hope that will be not fail start. At start I must say I make part 1 in Ray's Tutorial "How To Make A Game Like Fruit Ninja With Box2D and Cocos2D". But I wonder what when I want make more complex body with texture? Simple just add n b2FixtureDef to the same body. OK but what about texture? If I will take code from that tutorial it only fill last fixture. Probably it does not takes every b2Vec2 point. I was right, it did not. So quick refactor and from that -(id)initWithTexture:(CCTexture2D*)texture body:(b2Body*)body original:(BOOL)original { // gather all the vertices from our Box2D shape b2Fixture *originalFixture = body->GetFixtureList(); b2PolygonShape *shape = (b2PolygonShape*)originalFixture->GetShape(); int vertexCount = shape->GetVertexCount(); NSMutableArray *points = [NSMutableArray arrayWithCapacity:vertexCount]; for(int i = 0; i < vertexCount; i++) { CGPoint p = ccp(shape->GetVertex(i).x * PTM_RATIO, shape->GetVertex(i).y * PTM_RATIO); [points addObject:[NSValue valueWithCGPoint:p]]; } if ((self = [super initWithPoints:points andTexture:texture])) { _body = body; _body->SetUserData(self); _original = original; // gets the center of the polygon _centroid = self.body->GetLocalCenter(); // assign an anchor point based on the center self.anchorPoint = ccp(_centroid.x * PTM_RATIO / texture.contentSize.width, _centroid.y * PTM_RATIO / texture.contentSize.height); } return self; } I came up with that -(id)initWithTexture:(CCTexture2D*)texture body:(b2Body*)body original:(BOOL)original { int vertexCount = 0; //gather total number of b2Vect2 points b2Fixture *currentFixture = body->GetFixtureList(); while (currentFixture) { //new b2PolygonShape *shape = (b2PolygonShape*)currentFixture->GetShape(); vertexCount += shape->GetVertexCount(); currentFixture = currentFixture->GetNext(); } NSMutableArray *points = [NSMutableArray arrayWithCapacity:vertexCount]; // gather all the vertices from our Box2D shape b2Fixture *originalFixture = body->GetFixtureList(); while (originalFixture) { //new NSLog((NSString*)@"-"); b2PolygonShape *shape = (b2PolygonShape*)originalFixture->GetShape(); int currentVertexCount = shape->GetVertexCount(); for(int i = 0; i < currentVertexCount; i++) { CGPoint p = ccp(shape->GetVertex(i).x * PTM_RATIO, shape->GetVertex(i).y * PTM_RATIO); [points addObject:[NSValue valueWithCGPoint:p]]; } originalFixture = originalFixture->GetNext(); } if ((self = [super initWithPoints:points andTexture:texture])) { _body = body; _body->SetUserData(self); _original = original; // gets the center of the polygon _centroid = self.body->GetLocalCenter(); // assign an anchor point based on the center self.anchorPoint = ccp(_centroid.x * PTM_RATIO / texture.contentSize.width,_centroid.y * PTM_RATIO / texture.contentSize.height); } return self; } I was working for simple two fixtures body like b2BodyDef bodyDef; bodyDef.type = b2_dynamicBody; bodyDef.position = position; bodyDef.angle = rotation; b2Body *body = world->CreateBody(&bodyDef); b2FixtureDef fixtureDef; fixtureDef.density = 1.0; fixtureDef.friction = 0.5; fixtureDef.restitution = 0.2; fixtureDef.filter.categoryBits = 0x0001; fixtureDef.filter.maskBits = 0x0001; b2Vec2 vertices[] = { b2Vec2(0.0/PTM_RATIO,50.0/PTM_RATIO), b2Vec2(0.0/PTM_RATIO,0.0/PTM_RATIO), b2Vec2(50.0/PTM_RATIO,30.1/PTM_RATIO), b2Vec2(60.0/PTM_RATIO,60.0/PTM_RATIO) }; b2PolygonShape shape; shape.Set(vertices, 4); fixtureDef.shape = &shape; body->CreateFixture(&fixtureDef); b2Vec2 vertices2[] = { b2Vec2(20.0/PTM_RATIO,50.0/PTM_RATIO), b2Vec2(20.0/PTM_RATIO,0.0/PTM_RATIO), b2Vec2(70.0/PTM_RATIO,30.1/PTM_RATIO), b2Vec2(80.0/PTM_RATIO,60.0/PTM_RATIO) }; shape.Set(vertices2, 4); fixtureDef.shape = &shape; body->CreateFixture(&fixtureDef); But if I try put secondary shape upper than first it starting wierd, texture goes crazy. For example not mention about more complex shapes. What's more if shapes have one common point texture will not render for them at all [For that I use Physics Edytor like in tutorial part1] BTW. I use PolygonSprite and in method createWithWorld... another shapes. Uff.. Question So my question is, why texture coords are in such a mess up? It's my modify method or just wrong approach? Maybe I should remove duplicated from points array?

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• Keeping player aligned to grid in Pacman

  - by user17577

  I am making a Pacman game using XNA. The game is tile based, with each tile being 32 pixels. As the player moves, I need to know whenever it is perfectly on a tile (ie position of 32, 64, etc...) so that I can check to see if the next tile is free. I am using the following logic to test this. if (position.X % 32 == 0 && position.Y %32 == 0) { onTile = true; } I figure that I need to make the player's speed evenly divide 32. Everything works fine if I make the player's speed an integer such as 4 or 8. But if I make the speed something like 6.4, I end up with positions such as 64.00001, and my if statement no longer works correctly. How can I keep the player aligned with the grid, while allowing a wider range of player speeds than 1, 2, 4, 8, 16, and 32? Or is there some better way to go about this? Thanks

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• geomipmapping using displacement mapping (and glVertexAttribDivisor)

  - by Will

  I wake up with a clear vision, but sadly my laptop card doesn't do displacement mapping nor glVertexAttribDivisor so I can't test it out; I'm left sharing here: With geomipmapping, the grid at any factor is transposable - if you pass in an offset - say as a uniform - you can reuse the same vertex and index array again and again. If you also pass in the offset into the heightmap as a uniform, the vertex shader can do displacement mapping. If the displacement map is mipmapped, you get the advantages of trilinear filtering for distant maps. And, if the scenery is closer, rather than exposing that the you have a world made out of quads, you can use your transposable grid vertex array and indices to do vertex-shader interpolation (fancy splines) to do super-smooth infinite zoom? So I have some questions: does it work? In theory, in practice? does anyone do it? Does this technique have a name? Papers, demos, anything I can look at? does glVertexAttribDivisor mean that you can have a single glMultiDrawElementsEXT or similar approach to draw all your terrain tiles in one call rather than setting up the uniforms and emitting each tile? Would this offer any noticeable gains? does a heightmap that is GL_LUMINANCE take just one byte per pixel(=vertex)? (On mainstream cards, obviously. Does storage vary in practice?) Does going to the effort of reusing the same vertices and indices mean that you can basically fill the GPU RAM with heightmap and not a lot else, giving you either bigger landscapes or more detailed landscapes/meshes for the same bang? is mipmapping the displacement map going to work? On future cards? Is it going to introduce unsurmountable inaccuracies if it is enabled?

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• Novice prototyping a massive multiplayer webpage based gaming system

  - by Sean Hendlin

  I'm trying to build a website based game in which various pages of the site act as different areas of the game. I am wondering what you would recommended as a design structure. Which languages would be best if building what will hopefully becomes a massive system able to scale to massive amounts of users. I am wondering if and how various elements from differing languages could be meshed to interact with each other. For example could I use html5, javascript, and PHP? What about asp.net how might that factor in? I'm a newbie programmer but I've been working on this idea for years and I want to build it to reality. Your comments and suggestions are appreciated. P.S.: The game is not all graphics and animation (though flash like appearance and some animation would be nice). What I am thinking of is essentially a heavily gamified system of forms. And LOTS of data in many different categories cross referencing each-other. I'm not sure how to go about structuring the collection of data. Also while I know javascript can be used to process some functions, I'm wondering what sort of base system I would need to handle the server side processing of what I am expecting to be some pretty significant algorithm processing. That is to say I expect to have many many many functions and I'm not sure how to mange this using javascript. I feel like they would be forgotten, mixed up, disorganizes as they essentially only exist where they are coded. I guess I need to learn something of libraries? OK, Thank you! Is enough from me for now.

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• How can I selectively update XNA GameComponents?

  - by Bill

  I have a small 2D game I'm working on in XNA. So far, I have a player-controlled ship that operates on vector thrust and is terribly fun to spin around in circles. I've implemented this as a DrawableGameComponent and registered it with the game using game.Components.Add(this) in the Ship object constructor. How can I implement features like pausing and a menu system with my current implementation? Is it possible to set certain GameComponents to not update? Is this something for which I should even be using a DrawableGameComponent? If not, what are more appropriate uses for this?

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• How to Make Objects Fall Faster in a Physics Simulation

  - by David Dimalanta

  I used the collision physics (i.e. Box2d, Physics Body Editor) and implemented onto the java code. I'm trying to make the fall speed higher according to the examples: It falls slower if light object (i.e. feather). It falls faster depending on the object (i.e. pebble, rock, car). I decided to double its falling speed for more excitement. I tried adding the mass but the speed of falling is constant instead of gaining more speed. check my code that something I put under input processor's touchUp() return method under same roof of the class that implements InputProcessor and Screen: @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; } And take note, at show() method , the view size from the camera is at 720x1280: camera_1 = new OrthographicCamera(); camera_1.viewportHeight = 1280; camera_1.viewportWidth = 720; camera_1.position.set(camera_1.viewportWidth * 0.5f, camera_1.viewportHeight * 0.5f, 0f); camera_1.update(); I know it's a good idea to add weight to make the falling object falls faster once I released the finger from the touchUp() after I picked the object from the upper right of the screen but the speed remains either constant or slow. How can I solve this? Can you help?

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• Circular motion on low powered hardware

  - by Akroy

  I was thinking about platforms and enemies moving in circles in old 2D games, and I was wondering how that was done. I understand parametric equations, and it's trivial to use sin and cos to do it, but could an NES or SNES make real time trig calls? I admit heavy ignorance, but I thought those were expensive operations. Is there some clever way to calculate that motion more cheaply? I've been working on deriving an algorithm from trig sum identities that would only use precalculated trig, but that seems convoluted.

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• How to create an extensible rope in Box2D?

  - by Thomas

  Let's say I'm trying to create a ninja lowering himself down a rope, or pulling himself back up, all whilst he might be swinging from side to side or hit by objects. Basically like http://ninja.frozenfractal.com/ but with Box2D instead of hacky JavaScript. Ideally I would like to use a rope joint in Box2D that allows me to change the length after construction. The standard Box2D RopeJoint doesn't offer that functionality. I've considered a PulleyJoint, connecting the other end of the "pulley" to an invisible kinematic body that I can control to change the length, but PulleyJoint is more like a rod than a rope: it constrains maximum length, but unlike RopeJoint it constrains the minimum as well. Re-creating a RopeJoint every frame using a new length is rather inefficient, and I'm not even sure it would work properly in the simulation. I could create a "chain" of bodies connected by RotationJoints but that is also less efficient, and less robust. I also wouldn't be able to change the length arbitrarily, but only by adding and removing a whole number of links, and it's not obvious how I would connect the remainder without violating existing joints. This sounds like something that should be straightforward to do. Am I overlooking something?

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• Libgdx ParallaxScrolling and TiledMaps

  - by kirchhoff

  I implemented ParallaxScrolling for my SideScroller project, everything is working but the tiled map (the most important part!). I've been trying out everything but it doesn't work (see the code below). I'm using ParallaxCamera from GdxTests, it's working perfectly for the background layers. I can't explain myself properly in english, so I recorded 2 videos: Before parallaxScrolling After parallaxScrolling As you can see, now the platforms appear in the middle of the Y-axis. I've got a Map class with 2 tiled maps, so I need two renderers too: private TiledMapRenderer renderer1; private TiledMapRenderer renderer2; public void update(GameCamera camera) { renderer1.setView(camera.calculateParallaxMatrix(1f, 0f), camera.position.x - camera.viewportWidth / 2, **camera.position.y - camera.viewportHeight/2**, camera.viewportWidth, camera.viewportHeight); renderer2.setView(camera.calculateParallaxMatrix(1f, 0f), camera.position.x - camera.viewportWidth / 2, **camera.position.y - camera.viewportHeight/2**, camera.viewportWidth, camera.viewportHeight); } In bold, the code I think I should change. I've tried changing parameters, even adding hardcoded values, etc, but one of two: 1. Nothing happens. 2. Platforms disappear. Here is some aditional code. The render method: world.update(delta); parallaxBackground.update(camera); clear(0.5f, 0.7f, 1.0f, 1); batch.setProjectionMatrix(camera.calculateParallaxMatrix(0, 0)); batch.disableBlending(); batch.begin(); batch.draw(background, -(int)background.getRegionWidth()/2, -(int)background.getRegionHeight()/2); batch.end(); batch.enableBlending(); parallaxBackground.draw(batch, camera); renderer.render(batch);

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• Queries regarding Geometry Shaders

  - by maverick9888

  I am dealing with geometry shaders using GL_ARB_geometry_shader4 extension. My code goes like : GLfloat vertices[] = { 0.5,0.25,1.0, 0.5,0.75,1.0, -0.5,0.75,1.0, -0.5,0.25,1.0, 0.6,0.35,1.0, 0.6,0.85,1.0, -0.6,0.85,1.0, -0.6,0.35,1.0 }; glProgramParameteriEXT(psId, GL_GEOMETRY_INPUT_TYPE_EXT, GL_TRIANGLES); glProgramParameteriEXT(psId, GL_GEOMETRY_OUTPUT_TYPE_EXT, GL_TRIANGLE_STRIP); glLinkProgram(psId); glBindAttribLocation(psId,0,"Position"); glEnableVertexAttribArray (0); glVertexAttribPointer(0, 3, GL_FLOAT, 0, 0, vertices); glDrawArrays(GL_TRIANGLE_STRIP,0,4); My vertex shader is : #version 150 in vec3 Position; void main() { gl_Position = vec4(Position,1.0); } Geometry shader is : #version 150 #extension GL_EXT_geometry_shader4 : enable in vec4 pos[3]; void main() { int i; vec4 vertex; gl_Position = pos[0]; EmitVertex(); gl_Position = pos[1]; EmitVertex(); gl_Position = pos[2]; EmitVertex(); gl_Position = pos[0] + vec4(0.3,0.0,0.0,0.0); EmitVertex(); EndPrimitive(); } Nothing is rendered with this code. What exactly should be the mode in glDrawArrays() ? How does the GL_GEOMETRY_OUTPUT_TYPE_EXT parameter will affect glDrawArrays() ? What I expect is 3 vertices will be passed on to Geometry Shader and using those we construct a primitive of size 4 (assuming GL_TRIANGLE_STRIP requires 4 vertices). Can somebody please throw some light on this ?

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• Customize Colors for Sprites in Web Game

  - by NateDSaint

  So I'm working on an html5/javascript/css3-based game. Without going into too much detail, I'm thinking of having the characters be simple 8 or 16-bit style sprites, but I'd like to allow the user to customize the colors of their character. Here are some examples of what I'm talking about : http://jsfiddle.net/simurai/CGmCe/light/ http://www.splashnology.com/article/sprite-animation-in-css3/1485/ So the problem I'm having is two-fold: 1) Should I use something other than a sprite map for my characters, like actually draw them as shapes and animate them in a canvas element? That way I can fill the sprite with colors of the user's choosing? My fear there is that this would be inefficient as far as resources and also waste a lot of time hand-drawing everything, but could allow other customization (like height/width etc). 2) Are there potentially some web apis that would allow you to alter colors inside of a sprite? I suppose I could do it on the back-end with GD, but I'm trying to make it entirely in-browser (including local storage). It's not a definitive one-answer only question, but I'm hoping someone can suggest something they've seen that approaches the same problem from another angle or gives us a way to customize the sprites or manipulate them in some manner. Or avoid them altogether, and use a different method.

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• Understanding how OpenGL blending works

  - by yuumei

  I am attempting to understand how OpenGL (ES) blending works. I am finding it difficult to understand the documentation and how the results of glBlendFunc and glBlendEquation effect the final pixel that is written. Do the source and destination out of glBlendFunc get added together with GL_FUNC_ADD by default? This seems wrong because "basic" blending of GL_ONE, GL_ONE would output 2,2,2,2 then (Source giving 1,1,1,1 and dest giving 1,1,1,1). I have written the following pseudo-code, what have I got wrong? struct colour { float r, g, b, a; }; colour blend_factor( GLenum factor, colour source, colour destination, colour blend_colour ) { colour colour_factor; float i = min( source.a, 1 - destination.a ); // From http://www.khronos.org/opengles/sdk/docs/man/xhtml/glBlendFunc.xml switch( factor ) { case GL_ZERO: colour_factor = { 0, 0, 0, 0 }; break; case GL_ONE: colour_factor = { 1, 1, 1, 1 }; break; case GL_SRC_COLOR: colour_factor = source; break; case GL_ONE_MINUS_SRC_COLOR: colour_factor = { 1 - source.r, 1 - source.g, 1 - source.b, 1 - source.a }; break; // ... } return colour_factor; } colour blend( colour & source, colour destination, GLenum source_factor, // from glBlendFunc GLenum destination_factor, // from glBlendFunc colour blend_colour, // from glBlendColor GLenum blend_equation // from glBlendEquation ) { colour source_colour = blend_factor( source_factor, source, destination, blend_colour ); colour destination_colour = blend_factor( destination_factor, source, destination, blend_colour ); colour output; // From http://www.khronos.org/opengles/sdk/docs/man/xhtml/glBlendEquation.xml switch( blend_equation ) { case GL_FUNC_ADD: output = add( source_colour, destination_colour ); case GL_FUNC_SUBTRACT: output = sub( source_colour, destination_colour ); case GL_FUNC_REVERSE_SUBTRACT: output = sub( destination_colour, source_colour ); } return output; } void do_pixel() { colour final_colour; // Blending if( enable_blending ) { final_colour = blend( current_colour_output, framebuffer[ pixel ], ... ); } else { final_colour = current_colour_output; } } Thanks!

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• How can I implement an Iris Wipe effect?

  - by Vandell

  For those who doesn't know: An iris wipe is a wipe that takes the shape of a growing or shrinking circle. It has been frequently used in animated short subjects, such as those in the Looney Tunes and Merrie Melodies cartoon series, to signify the end of a story. When used in this manner, the iris wipe may be centered around a certain focal point and may be used as a device for a "parting shot" joke, a fourth wall-breaching wink by a character, or other purposes. Example from flasheff.com Your answer may or may not include a coding sample, a language agnostic explanation is considered enough.

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• Split a 2D scene in layers or have a z coordinate

  - by Bane

  I am in the process of writing a 2D game engine, and a dilemma emerged. Let me explain the situation... I have a Scene class, to which various objects can be added (Drawable, ParticleEmitter, Light2D, etc), and as this is a 2D scene, things will obviously be drawn over each other. My first thought was that I could have basic add and remove methods, but I soon realized that then there would be no way for the programmer to control the order in which things were drawn. So I can up with two options, each with its pros and cons. A) Would be to split the scene in layers. By that I mean instead of having the scene be a container of objects, have it be a container of layers, which are in turn the containers of objects. B) Would require to have some kind of z-coordinate, and then have the scene sorted so objects with lower z get drawn first. Option A is pretty solid, but the problem is with the lights. In what layer do I add it? Does it work cross-layer? On all bottom layers? And I still need the Z coordinate to calculate the shadow! Option B would require me to change all my code from having Vector2D positions, to some kind of class that inherits from Vector2D and adds a z coordinate to it (I don't want it to be a Vector3D because I still need all the same methods the 2D kind has, just with .z clamped on). Am I missing something? Is there an alternative to these methods? I'm working in Javascript, if that makes a difference.

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