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  • OpenGL ES 2. How do I Create a Basic Fading Streak Effect?

    - by dugla
    For the iPad app I am writing using OpenGL ES 2 I have a single quad - shaded using GLSL - that is dragged around the screen. Very basic. This works fine. But is rather boring. I want to increase the coolness a bit in the following way: when the user drags the quad it leaves a streak behind that fades over time. Continuous dragging would be a bit like a streaking comet across the night sky. What is the simplest way to implement this? Thanks.

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  • How to render a retro-like pixel graphics from 3d models?

    - by momijigari
    I was wondering if there's a possibility to render a retro-pixel-like graphics from 3d model in real time? I'm talking about the Starfarer-like graphics. I know it's hand drawn, and it's 2d. But if I need a 3d objects with the same aesthetics? I'm currently working with Flash. But I don't need any ready-solutions, I just want to understand the principle from any other platform if there is one. So if anybody met anything like this I would appreciate your help. (If it's not possible to do in real time, I could at least pre-render a sequence of sprites. It would be much better than creating hundreds of hand-drawn ones)

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  • libgdx draw issue and animation

    - by johnny-b
    it seems as though i cannot get the draw method to work??? it seems as though the bullet.draw(batcher) does not work and i cannot understand why as the bullet is a sprite. i have made a Sprite[] and added them as animation. could that be it? i tried batcher.draw(AssetLoader.bulletAnimation.getKeyFrame(runTime), bullet.getX(), bullet.getY(), bullet.getOriginX() / 2, bullet.getOriginY() / 2, bullet.getWidth(), bullet.getHeight(), 1, 1, bullet.getRotation()); but that dont work, the only way it draws is this batcher.draw(AssetLoader.bulletAnimation.getKeyFrame(runTime), bullet.getX(), bullet.getY()); below is the code. // this is in a Asset Class texture = new Texture(Gdx.files.internal("SpriteN1.png")); texture.setFilter(TextureFilter.Nearest, TextureFilter.Nearest); bullet1 = new Sprite(texture, 380, 350, 45, 20); bullet1.flip(false, true); bullet2 = new Sprite(texture, 425, 350, 45, 20); bullet2.flip(false, true); Sprite[] bullets = { bullet1, bullet2 }; bulletAnimation = new Animation(0.06f, bullets); bulletAnimation.setPlayMode(Animation.PlayMode.LOOP); // this is the GameRender class public class GameRender() { private Bullet bullet; private Ball ball; public GameRenderer(GameWorld world) { myWorld = world; cam = new OrthographicCamera(); cam.setToOrtho(true, 480, 320); batcher = new SpriteBatch(); // Attach batcher to camera batcher.setProjectionMatrix(cam.combined); shapeRenderer = new ShapeRenderer(); shapeRenderer.setProjectionMatrix(cam.combined); // Call helper methods to initialize instance variables initGameObjects(); initAssets(); } private void initGameObjects() { ball = GameWorld.getBall(); bullet = myWorld.getBullet(); scroller = myWorld.getScroller(); } private void initAssets() { ballAnimation = AssetLoader.ballAnimation; bulletAnimation = AssetLoader.bulletAnimation; } public void render(float runTime) { Gdx.gl.glClearColor(0, 0, 0, 1); Gdx.gl.glClear(GL30.GL_COLOR_BUFFER_BIT); batcher.begin(); // Disable transparency // This is good for performance when drawing images that do not require // transparency. batcher.disableBlending(); // The ball needs transparency, so we enable that again. batcher.enableBlending(); batcher.draw(AssetLoader.ballAnimation.getKeyFrame(runTime), ball.getX(), ball.getY(), ball.getWidth(), ball.getHeight()); batcher.draw(AssetLoader.bulletAnimation.getKeyFrame(runTime), bullet.getX(), bullet.getY()); // End SpriteBatch batcher.end(); } } // this is the gameworld class public class GameWorld { public static Ball ball; private Bullet bullet; private ScrollHandler scroller; public GameWorld() { ball = new Ball(480, 273, 32, 32); bullet = new Bullet(10, 10); scroller = new ScrollHandler(0); } public void update(float delta) { ball.update(delta); bullet.update(delta); scroller.update(delta); } public static Ball getBall() { return ball; } public ScrollHandler getScroller() { return scroller; } public Bullet getBullet() { return bullet; } } is there anyway so make the sprite work?

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  • Learning OpenGL GLSL - VAO buffer problems?

    - by Bleary
    I've just started digging through OpenGL and GLSL, and now stumbled on something I can't get my head around this one!? I've stepped back to loading a simple cube and using a simple shader on it, but the result is triangles drawn incorrectly and/or missing. The code I had working perfectly on meshes, but was attempting to move to using VAOs so none of the code for storing the vertices and indices has changed. http://i.stack.imgur.com/RxxZ5.jpg http://i.stack.imgur.com/zSU50.jpg What I have for creating the VAO and buffers is this //Create the Vertex array object glGenVertexArrays(1, &vaoID); // Finally create our vertex buffer objects glGenBuffers(VBO_COUNT, mVBONames); glBindVertexArray(vaoID); // Save vertex attributes into GPU glBindBuffer(GL_ARRAY_BUFFER, mVBONames[VERTEX_VBO]); // Copy data into the buffer object glBufferData(GL_ARRAY_BUFFER, lPolygonVertexCount*VERTEX_STRIDE*sizeof(GLfloat), lVertices, GL_STATIC_DRAW); glEnableVertexAttribArray(pos); glVertexAttribPointer(pos, 3, GL_FLOAT, GL_FALSE, VERTEX_STRIDE*sizeof(GLfloat),0); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, mVBONames[INDEX_VBO]); glBufferData(GL_ELEMENT_ARRAY_BUFFER, lPolygonCount*sizeof(unsigned int), lIndices, GL_STATIC_DRAW); glBindVertexArray(0); And the code for drawing the mesh. glBindVertexArray(vaoID); glUseProgram(shader->programID); GLsizei lOffset = mSubMeshes[pMaterialIndex]->IndexOffset*sizeof(unsigned int); const GLsizei lElementCount = mSubMeshes[pMaterialIndex]->TriangleCount*TRIAGNLE_VERTEX_COUNT; glDrawElements(GL_TRIANGLES, lElementCount, GL_UNSIGNED_SHORT, reinterpret_cast<const GLvoid*>(lOffset)); // All the points are indeed in the correct place!? //glPointSize(10.0f); //glDrawElements(GL_POINTS, lElementCount, GL_UNSIGNED_SHORT, 0); glUseProgram(0); glBindVertexArray(0); Eyes have become bleary looking at this today so any thoughts or a fresh set of eyes would be greatly appreciated.

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  • Why does my VertexDeclaration apparently not contain Position0?

    - by Phil
    I'm trying to get my code from calling each individual draw call down to using at least a VertexBuffer, and preferably an indexBuffer, but now that I'm attempting to test my code, I'm getting the error: The current vertex declaration does not include all the elements required by the current vertex shader. Position0 is missing. Which makes absolutely no sense to me, as my VertexDeclaration is: public readonly static VertexDeclaration VertexDeclaration = new VertexDeclaration( new VertexElement(0, VertexElementFormat.Vector3, VertexElementUsage.Position, 0), new VertexElement(sizeof(float) * 3, VertexElementFormat.Color, VertexElementUsage.Color, 0), new VertexElement(sizeof(float) * 3 + 4, VertexElementFormat.Vector3, VertexElementUsage.Normal, 0) ); Which clearly contains the information. I am attempting to draw with the following lines: VertexBuffer vb = new VertexBuffer(GraphicsDevice, VertexPositionColorNormal.VertexDeclaration, c.VertexList.Count, BufferUsage.WriteOnly); IndexBuffer ib = new IndexBuffer(GraphicsDevice, typeof(int), c.IndexList.Count, BufferUsage.WriteOnly); vb.SetData<VertexPositionColorNormal>(c.VertexList.ToArray()); ib.SetData<int>(c.IndexList.ToArray()); GraphicsDevice.DrawIndexedPrimitives(PrimitiveType.TriangleList, 0, 0, vb.VertexCount, 0, c.IndexList.Count/3); Where c is a Chunk class containing an 8x8x8 array of boxes. Full code is available at https://github.com/mrbaggins/Box/tree/ProperMeshing/box/box. Relevant locations are Chunk.cs (Contains the VertexDeclaration) and Game1.cs (Draw() is in Lines 230-250). Not much else of relevance to this problem anywhere else. Note that large commented sections are from old version of drawing.

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  • How do I get my polygons to be lighted by either side?

    - by Molmasepic
    Okay, I am using Ogre3D and Gorilla(2D library for ogre3D) and I am making Gorilla::Screenrenderables in the open scene. The problem that I am having is that when I make a light and have my SR(screenrenderable) near it, it does not light up unless the face of the SR is facing the light... I am wondering if there is a way to maybe set the material or code(which would be harder) so the SR is lit up whether the vertices of the polygon are facing the light or not. I feel it is possible but the main obstacle is how I would go about doing this.

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  • HLSL: Pack 4 values into 32 bit float.

    - by TheBigO
    I can't find any useful information on packing 4 values into a 32 bit float in HLSL. Ideally, what I want to be able to do in HLSL is: float4 values = ... // Some values where each component is between 0 and 1. float packedValues = pack32R(values); float4 values2 = unpack32R(packedValues); I realize that there will be precision limitations, and performance tradeoffs between different precisions in different methods. I'm just wondering what ideas are out there.

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  • Circle vs Edge collision detection / resolution

    - by topheman
    I made a javascript class Ball.js that handles physics interactions betweens balls as well as painting. In the v1.0, the ball vs ball collision detection and resolution is well handled. In the next version (v2), I'm trying to add edgeCollision handling. I'm having some problems, maybe you will be able to help me. All the v2 branch source code is on github repository : https://github.com/topheman/Ball.js/tree/v2 The v2 demos (where you can see the bug I will be talking about) : http://labs.topheman.com/Ball-v2/#help As you will see on the demo, I have two major problems that I'm having a really hard time to solve on Ball.js : method resolveEdgeCollision : bounce angle is inconsistent method checkEdgeCollision : if the ball's velocity (the length that it runs each frame) is higher than its diameter, eventually, it will pass through an edge, without triggering any collision Any Ideas ?...

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  • How to remove a box2d body when collision happens?

    - by Ayham
    I’m still new to java and android programming and I am having so much trouble Removing an object when collision happens. I looked around the web and found that I should never handle removing BOX2D bodies during collision detection (a contact listener) and I should add my objects to an arraylist and set a variable in the User Data section of the body to delete or not and handle the removing action in an update handler. So I did this: First I define two ArrayLists one for the faces and one for the bodies: ArrayList<Sprite> myFaces = new ArrayList<Sprite>(); ArrayList<Body> myBodies = new ArrayList<Body>(); Then when I create a face and connect that face to its body I add them to their ArrayLists like this: face = new AnimatedSprite(pX, pY, pWidth, pHeight, this.mBoxFaceTextureRegion); Body BoxBody = PhysicsFactory.createBoxBody(mPhysicsWorld, face, BodyType.DynamicBody, objectFixtureDef); mPhysicsWorld.registerPhysicsConnector(new PhysicsConnector(face, BoxBody, true, true)); myFaces.add(face); myBodies.add(BoxBody); now I add a contact listener and an update handler in the onloadscene like this: this.mPhysicsWorld.setContactListener(new ContactListener() { private AnimatedSprite face2; @Override public void beginContact(final Contact pContact) { } @Override public void endContact(final Contact pContact) { } @Override public void preSolve(Contact contact,Manifold oldManifold) { } @Override public void postSolve(Contact contact,ContactImpulse impulse) { } }); scene.registerUpdateHandler(new IUpdateHandler() { @Override public void reset() { } @Override public void onUpdate(final float pSecondsElapsed) { } }); My plan is to detect which two bodies collided in the contact listener by checking a variable from the user data section of the body, get their numbers in the array list and finally use the update handler to remove these bodies. The questions are: Am I using the arraylist correctly? How to add a variable to the User Data (the code please). I tried removing a body in this update handler but it still throws me NullPointerException , so what is the right way to add an update handler and where should I add it. Any other advices to do this would be great. Thanks in advance.

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  • Efficiently rendering to 3D texture

    - by TravisG
    I have an existing depth texture and some other color textures, and want to process the information in them by rendering to a 3D texture (based on the depth contained in the depth texture, i.e. a point at (x/y) in the depth texture will be rendered to (x/y/texture(depth,uv)) in the 3D texture). Simply doing one manual draw call for each slice of the 3D texture (via glFramebufferTextureLayer) is terribly slow, since I don't know beforehand to what slice of the 3D texture a given texel from one of the color textures or the depth texture belongs. This means the entire process is effectively for each slice for each texel in depth texture process color textures and render to slice So I have to sample the depth texture completely per each slice, and I also have to go through the processing (at least until to discard;) for all texels in it. It would be much faster if I could rearrange the process to for each texel in depth texture figure out what slice it should end up in process color textures and render to slice Is this possible? If so, how? What I'm actually trying to do: the color textures contain lighting information (as seen from light view, it's a reflective shadow map). I want to accumulate that information in the 3D texture and then later use it to light the scene. More specifically I'm trying to implement Cryteks Light Propagation Volumes algorithm.

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  • How can I generate signed distance fields (2D) in real time, fast?

    - by heishe
    In a previous question, it was suggested that signed distance fields can be precomputed, loaded at runtime and then used from there. For reasons I will explain at the end of this question (for people interested), I need to create the distance fields in real time. There are some papers out there for different methods which are supposed to be viable in real-time environments, such as methods for Chamfer distance transforms and Voronoi diagram-approximation based transforms (as suggested in this presentation by the Pixeljunk Shooter dev guy), but I (and thus can be assumed a lot of other people) have a very hard time actually putting them to use, since they're usually long, largely bloated with math and not very algorithmic in their explanation. What algorithm would you suggest for creating the distance fields in real-time (favourably on the GPU) especially considering the resulting quality of the distance fields? Since I'm looking for an actual explanation/tutorial as opposed to a link to just another paper or slide, this question will receive a bounty once it's eligible for one :-). Here's why I need to do it in real time: There's something else:

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  • Circle collision detection and Vector math: HELP?

    - by Griffin
    Hey so i'm currently going through the wildbunny blog to learn about collision detection, but i'm a bit confused on how the vectors he's talking about come into play QUOTED BLOG: p = ||A-B|| – (r1+r2) The two spheres are penetrating by distance p. We would also like the penetration vector so that we can correct the penetration once we discover it. This is the vector that moves both circles to the point where they just touch, correcting the penetration. Importantly it is not only just a vector that does this, it is the only vector which corrects the penetration by moving the minimum amount. This is important because we only want to correct the error, not introduce more by moving too much when we correct, or too little. N = (A-B) / ||A-B|| P = N*p Here we have calculated the normalised vector N between the two centres and the penetration vector P by multiplying our unit direction by the penetration distance. Ok so i understand that p is the distance each circle is penetrating each other, but i don't get what exactly N and P is. it seems to me N is just the coordinates of the 3rd point of the right trianlge formed by point A and B (A-B) then being divided by the hypotenuse of that triangle or distance between A and B (||A-B||) Whats the significance of this? Also, what is the penetration vector used for? It seems to me like a movement that one of the circles would perform to get un-penetrated.

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  • Algorithms for rainfall + river creation in procedurally generated terrain

    - by Peck
    I've recently become fascinated by the things that can be done with procedurally terrain and have started experimenting with world building a bit. I'd like to be able to make worlds something like Dwarf fortress with biomes created from meshing together various maps. So first step has been done. Using the diamond-square algorithm I've created some nice hieghtmaps. Next step is I would like to add some water features and have them somewhat realistically generated with rainfall. I've read about a few different approaches such as starting at the high points of the map, and "stepping" down to the lowest neighboring point, pooling/eroding as it works its way down to sea level. Are there any documented algorithms with this or are they more off the cuff? Would love any advice/thoughts.

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  • forward motion car physics - gradual slow

    - by spartan2417
    Im having trouble creating realistic car movements in xna 4. Right now i have a car going forward and hitting a terminal velocity which is fine but when i release the up key i need to the car to slow down gradually and then come to a stop. Im pretty sure this is easy code but i cant seem to get it to work the code - update if (Keyboard.GetState().IsKeyDown(Keys.Up)) { double elapsedTime = gameTime.ElapsedGameTime.Milliseconds; CalcTotalForce(); Acceleration = Vector2.Divide(CalcTotalForce(), MASS); Velocity = Vector2.Add(Velocity, Vector2.Multiply(Acceleration, (float)(elapsedTime))); Position = Vector2.Add(Position, Vector2.Multiply(Velocity, (float)(elapsedTime))); } added functions public Vector2 CalcTraction() { //Traction force = vector direction * engine force return Vector2.Multiply(forwardDirection, ENGINE_FORCE); } public Vector2 CalcDrag() { //Drag force = constdrag * velocity * speed return Vector2.Multiply(Vector2.Multiply(Velocity, DRAG_CONST), Velocity.Y); } public Vector2 CalcRoll() { //roll force = const roll * velocity return Vector2.Multiply(Velocity, ROLL_CONST); } public Vector2 CalcTotalForce() { //total force = traction + (-drag) + (-rolling) return Vector2.Add(CalcTraction(), Vector2.Add(-CalcDrag(), -CalcRoll())); } anyone have any ideas?

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  • Unable to find good parameters for behavior of a puck in Farseer

    - by Krumelur
    EDIT: I have tried all kinds of variations now. The last one was to adjust the linear velocity in each step: newVel = oldVel * 0.9f - all of this including your proposals kind of work, however in the end if the velocity is little enough, the puck sticks to the wall and slides either vertically or horizontally. I can't get rid of this behavior. I want it to bounce, no matter how slow it is. Retitution is 1 for all objects, Friction is 0 for all. There is no gravity. What am I possibly doing wrong? In my battle to learn and understand Farseer I'm trying to setup a simple Air Hockey like table with a puck on it. The table's border body is made up from: Vertices aBorders = new Vertices( 4 ); aBorders.Add( new Vector2( -fHalfWidth, fHalfHeight ) ); aBorders.Add( new Vector2( fHalfWidth, fHalfHeight ) ); aBorders.Add( new Vector2( fHalfWidth, -fHalfHeight ) ); aBorders.Add( new Vector2( -fHalfWidth, -fHalfHeight ) ); FixtureFactory.AttachLoopShape( aBorders, this ); this.CollisionCategories = Category.All; this.CollidesWith = Category.All; this.Position = Vector2.Zero; this.Restitution = 1f; this.Friction = 0f; The puck body is defined with: FixtureFactory.AttachCircle( DIAMETER_PHYSIC_UNITS / 2f, 0.5f, this ); this.Restitution = 0.1f; this.Friction = 0.5f; this.BodyType = FarseerPhysics.Dynamics.BodyType.Dynamic; this.LinearDamping = 0.5f; this.Mass = 0.2f; I'm applying a linear force to the puck: this.oPuck.ApplyLinearImpulse( new Vector2( 1f, 1f ) ); The problem is that the puck and the walls appear to be sticky. This means that the puck's velocity drops to zero to quickly below a certain velocity. The puck gets reflected by the walls a couple of times and then just sticks to the left wall and continues sliding downwards the left wall. This looks very unrealistic. What I'm really looking for is that a puck-wall-collision does slow down the puck only a tiny little bit. After tweaking all values left and right I was wondering if I'm doing something wrong. Maybe some expert can comment on the parameters?

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  • Optimal way to learn DirectX?

    - by BluePhase
    I am finding it very difficult to learn DirectX 11. The MSDN website is just full of unorganized information that doesn't seem to help at all. I am particularly looking for something that explains many if not all aspects of developing with DirectX 11. I have been searching for weeks and still come up empty. I have found some books but they don't really explain the fundamentals of the language at all. Thanks in advanced.

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  • SRV from UAV on the same texture in directx

    - by notabene
    I'm programming gpgpu raymarching (volumetric raytracing) in directx11. I succesfully perform compute shader and save raymarched volume data to texture. Then i want to use same texture as SRV in normal graphic pipeline. But it doesnt work, texture is not visible. Texture is ok, when i save it file it is what i expect. Texture rendering is ok too, when i render another SRV, it is ok. So problem is only in UAV-SRV. I also triple checked if pointers are ok. Please help, i'm getting mad about this. Here is some code: //before dispatch D3D11_TEXTURE2D_DESC textureDesc; ZeroMemory( &textureDesc, sizeof( textureDesc ) ); textureDesc.Width = xr; textureDesc.Height = yr; textureDesc.MipLevels = 1; textureDesc.ArraySize = 1; textureDesc.SampleDesc.Count = 1; textureDesc.SampleDesc.Quality = 0; textureDesc.Usage = D3D11_USAGE_DEFAULT; textureDesc.BindFlags = D3D11_BIND_UNORDERED_ACCESS | D3D11_BIND_SHADER_RESOURCE ; textureDesc.Format = DXGI_FORMAT_R32G32B32A32_FLOAT; D3D->CreateTexture2D( &textureDesc, NULL, &pTexture ); D3D11_UNORDERED_ACCESS_VIEW_DESC viewDescUAV; ZeroMemory( &viewDescUAV, sizeof( viewDescUAV ) ); viewDescUAV.Format = DXGI_FORMAT_R32G32B32A32_FLOAT; viewDescUAV.ViewDimension = D3D11_UAV_DIMENSION_TEXTURE2D; viewDescUAV.Texture2D.MipSlice = 0; D3DD->CreateUnorderedAccessView( pTexture, &viewDescUAV, &pTextureUAV ); //the getSRV function after dispatch. D3D11_SHADER_RESOURCE_VIEW_DESC srvDesc ; ZeroMemory( &srvDesc, sizeof( srvDesc ) ); srvDesc.Format = DXGI_FORMAT_R32G32B32A32_FLOAT; srvDesc.ViewDimension = D3D11_SRV_DIMENSION_TEXTURE2D; srvDesc.Texture2D.MipLevels = 1; D3DD->CreateShaderResourceView( pTexture, &srvDesc, &pTextureSRV);

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  • OpenGL + Allegro. Moving from software drawing X Y to openGL is confusing

    - by Aaron
    Having a fair bit of trouble. I'm used to Allegro and drawing sprites on a bitmap buffer at X Y coords. Now I've started a test project with OpenGL and its weird. Basically, as far as I know, theirs many ways to draw stuff in OpenGL. At the moment, I think I'm creating a Quad? Whatever that is, and I think Ive given it a texture of a bitmap and them im drawing that: GLuint gl_image; bitmap = load_bitmap("cat.bmp", NULL); gl_image = allegro_gl_make_texture_ex(AGL_TEXTURE_MASKED, bitmap, GL_RGBA); glBindTexture(GL_TEXTURE_2D, gl_image); glBegin(GL_QUADS); glColor4ub(255, 255, 255, 255); glTexCoord2f(0, 0); glVertex3f(-0.5, 0.5, 0); glTexCoord2f(1, 0); glVertex3f(0.5, 0.5, 0); glTexCoord2f(1, 1); glVertex3f(0.5, -0.5, 0); glTexCoord2f(0, 1); glVertex3f(-0.5, -0.5, 0); glEnd(); So yeah. So I got a few questions: Is this the best way of drawing a sprite? Is it suitable? The big question: Can anyone help / Does anyone know any tutorials on this weird coordinate thing? If it even is that. It's vastly different from XY, but I want to learn it. I was thinking maybe I could learn how this weird positioning stuff works, and then write a function to try and translate it to X and Y coords. Thats about it. I'm still trying to figure it all out on my own but any contributions you guys can make would be greatly appreciated =D Thanks!

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  • Making efficeint voxel engines using "chunks"

    - by Wardy
    Concept I'm currently looking in to how voxel engines work with a view to possibly making one myself. I see a lot of stuff like this ... https://sites.google.com/site/letsmakeavoxelengine/home/chunks ... which talks about how to go about reducing the draw calls. What I can't seem to understand is how it actually saves draw call counts on the basis of the logic being something like this ... Without chunks foreach voxel in myvoxels DrawIfVisible() With Chunks foreach chunk in mychunks DrawIfVisible() which then does ... foreach voxel in myvoxels DrawIfVisible() So surely you saved nothing ?!?! You still make a draw call for each visible voxel do you not? A visible voxel needs a draw call in either scenario. The only real saving I can see is that the logic that evaluates a chunk will be able to determine if a large number of voxels are visible or not effectively saving a bit of "is this chunk visible" cpu time. But it's the draw calls that interest me ... The fewer of those, the faster the application. EDIT: In case it makes any difference I will probably be using XNA (DX not OpenGL) for my engine so don't consider my choice of example in the link above my choice of technology. But this question is such that I doubt it would matter.

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  • Check for bodies within a specific circle in Box2D

    - by ltjax
    I'm trying to find positions to insert new bodies into my world. For that, I'd like to have a "free" spot where this body wouldn't overlap with anything else. So my plan was to sample "random" positions and check whether they overlap with my "potential" new body. Since my bodies are always circular, I'd need to test within a given circle. So far, the only way to use box2d for this seems to use b2World::QueryAABB around my circle and manually doing an overlap test with all the fixtures it gives me (Box2D doesn't event seem to allow me to tap into its overlapping tests?!). It seems to me like Box2D should already provide such functionality - is there a way that lets me do this without reinventing most of the wheel again?

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  • exact point on a rotating sphere

    - by nkint
    I have a sphere that represents the Earth textured with real pictures. It's rotating around the x axis, and when user click down it has to show me the exact place he clicked on. For example if he clicked on Singapore the system should be able to: understand that user clicked on the sphere (OK, I'll do it with unProject) understand where user clicked on the sphere (ray-sphere collision?) and take into account the rotation transform sphere-coordinate to some coordinate system good for some web-api service ask to api (OK, this is the simpler thing for me ;-) some advice?

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  • Understanding IDAT chunk of PNG file format

    - by DRapp
    From the sample image below, I have a border in yellow just for display purposes only. The actual .png file is a simple black/white image 3 pixels by 3 pixels. I was originally thinking to try as a 2x2, but that would not help trying to interpret low/hi vs hi/low drawing stream. At least this way, I would have two black, one white from the top, or one white, two black from the bottom.. So I read the chunks of data, get to the IDAT chunk, decode that (zlib) and come up with 12 bytes as follows 00 20 00 40 00 80 So, my question, how does the above get broken down into the 3x3 black and white sample... Also, it is saved in palette format and properly recognizes the bit depth of 1 and color palette of 2... color pallet[0] is RGBA all zeros. Palette1 has RGBA of 255, 255, 255, 0 I'll eventually get into the multiple other depth formats later, just wanted to start with what would expect to be the easiest. Part II. Any guidance on handling the other depth formats would help if anything special to be considered especially regarding alpha channel (which I am already looking for in the palette) that might trip me up.

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  • Player sprite moving slower on iPhone 4

    - by nvillec
    I just finished getting movement/jump animation for a player sprite in Xcode using Cocos2D. The basic movement algorithm is a timer that updates every 0.01 sec, changing the sprite position to (sprite.position.x + xVel, sprite.position.y + yVel). Each time a movement button is tapped, the appropriate velocity (initialized to 0) is changed to whatever speed I choose, then a stop movement button returns the velocity to 0. It's not an ideal solution but I'm very new at this and stoked to at least have that working with little help from the internet. So I may not have explained that perfectly, but it is in fact working to my satisfaction in Xcode's iPhone Simulator, however when I build it for my device and run it on my phone, the sprite's movement speed is noticeably slower than in Xcode. At first I thought it must have to do with the resolution of the iPhone 4, making the sprite's movement path twice as long, but I found that if I pull up the multitask bar, then return to the app the speed will sometimes jump back to normal. My second theory was that the code is just inefficient and is bogging the processes down, but I would see this reflected in the frame rate wouldn't I? It stays at 59-60 the whole time, and the spritesheet animation runs at the correct speed. Has anyone experienced this? Is this a really obvious issue that I'm completely missing? Any help (or tips for optimizing my approach to movement) would be much appreciated!

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  • About floating point precision and why do we still use it

    - by system_is_b0rken
    Floating point has always been troublesome for precision on large worlds. This article explains behind-the-scenes and offers the obvious alternative - fixed point numbers. Some facts are really impressive, like: "Well 64 bits of precision gets you to the furthest distance of Pluto from the Sun (7.4 billion km) with sub-micrometer precision. " Well sub-micrometer precision is more than any fps needs (for positions and even velocities), and it would enable you to build really big worlds. My question is, why do we still use floating point if fixed point has such advantages? Most rendering APIs and physics libraries use floating point (and suffer it's disadvantages, so developers need to get around them). Are they so much slower? Additionally, how do you think scalable planetary engines like outerra or infinity handle the large scale? Do they use fixed point for positions or do they have some space dividing algorithm?

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  • libgdx collision detection / bounding the object

    - by johnny-b
    i am trying to get collision detection so i am drawing a red rectangle to see if it is working, and when i do the code below in the update method. to check if it is going to work. the position is not in the right place. the red rectangle starts from the middle and not at the x and y point?Huh so it draws it wrong. i also have a getter method so nothing wrong there. bullet.set(getX(), getY(), getOriginX(), getOriginY()); this is for the render shapeRenderer.begin(ShapeType.Filled); shapeRenderer.setColor(Color.RED); shapeRenderer.rect(bullet.getX(), bullet.getY(), bullet.getOriginX(), bullet.getOriginY(), 15, 5, bullet.getRotation()); shapeRenderer.end(); i have tried to do it with a circle but the circle draws in the middle and i want it to be at the tip of the bullet. at the front of the bullet. x, y point. boundingCircle.set(getX() + getOriginX(), getY() + getOriginY(), 4.0f); shapeRenderer.begin(ShapeType.Filled); shapeRenderer.setColor(Color.RED); shapeRenderer.circle(bullet.getBoundingCircle().x, bullet.getBoundingCircle().y, bullet.getBoundingCircle().radius); shapeRenderer.end(); thank you need it to be of the x and y as the bullet is in the middle of the sprite when drawn originally via paint.

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