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• Get Specific depth values in Kinect (XNA)

  - by N0xus

  I'm currently trying to make a hand / finger tracking with a kinect in XNA. For this, I need to be able to specify the depth range I want my program to render. I've looked about, and I cannot see how this is done. As far as I can tell, kinect's depth values only work with pre-set ranged found in the depthStream. What I would like to do is make it modular so that I can change the depth range my kinect renders. I know this has been down before but I can't find anything online that can show me how to do this. Could someone please help me out? I have made it possible to render the standard depth view with the kinect, and the method that I have made for converting the depth frame is as follows (I've a feeling its something in here I need to set) private byte[] ConvertDepthFrame(short[] depthFrame, DepthImageStream depthStream, int depthFrame32Length) { int tooNearDepth = depthStream.TooNearDepth; int tooFarDepth = depthStream.TooFarDepth; int unknownDepth = depthStream.UnknownDepth; byte[] depthFrame32 = new byte[depthFrame32Length]; for (int i16 = 0, i32 = 0; i16 < depthFrame.Length && i32 < depthFrame32.Length; i16++, i32 += 4) { int player = depthFrame[i16] & DepthImageFrame.PlayerIndexBitmask; int realDepth = depthFrame[i16] >> DepthImageFrame.PlayerIndexBitmaskWidth; // transform 13-bit depth information into an 8-bit intensity appropriate // for display (we disregard information in most significant bit) byte intensity = (byte)(~(realDepth >> 8)); if (player == 0 && realDepth == 00) { // white depthFrame32[i32 + RedIndex] = 255; depthFrame32[i32 + GreenIndex] = 255; depthFrame32[i32 + BlueIndex] = 255; } // omitted other if statements. Simple changed the color of the pixels if they went out of the pre=set depth values else { // tint the intensity by dividing by per-player values depthFrame32[i32 + RedIndex] = (byte)(intensity >> IntensityShiftByPlayerR[player]); depthFrame32[i32 + GreenIndex] = (byte)(intensity >> IntensityShiftByPlayerG[player]); depthFrame32[i32 + BlueIndex] = (byte)(intensity >> IntensityShiftByPlayerB[player]); } } return depthFrame32; } I have a strong hunch it's something I need to change in the int player and int realDepth values, but i can't be sure.

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• Box2d world width and height ratio with screen width and height

  - by Sujith

  I have view, for example GameView which extends SurfaceView . I have integrated Box2D physics in GameView. I have two widths , GameView width, height and Box2D physics world width ,height. I need to get the position of box2d world with the GameView co-ordinates. For example, Total width of screen = 240 Total height of screen = 320 Screen points needed to be mapped onto box2d co-ordinates (x,y) = 127, 139 For this i need to get the max width and height of the Box2d physics world. Is there is any way to get the max width and height of Box2d world. or Can i limit the width and height of box2d world within the screen resolution.

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• Isometric algorithm producing tiles in wrong draw order

  - by David

  I've been toying with isometric and I just cant get the tiles to be in the right order. I'm probably missing something obvious and I just can't see it. Even at the risk of looking stupid, here's my code: for (int i = 0; i < Tile.MapSize; i++) { for (int j = 0; j < Tile.MapSize; j++) { spriteBatch.Draw( Tile.TileSetTexture, new Rectangle( (-j * Tile.TileWidth / 2) + (i * Tile.TileWidth / 2), (i * (Tile.TileHeight - 9) / 2) - (-j * (Tile.TileHeight - 9) / 2), Tile.TileWidth, Tile.TileHeight), Tile.GetSourceRectangle(tileID), Color.White, 0.0f, new Vector2(-350, -60), SpriteEffects.None, 1.0f); } } And here's what I end up with: messed up map Yep, bit of an issue. If anyone could help, I'd appreciate it.

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• What happened to .fx files in D3D11?

  - by bobobobo

  It seems they completely ruined .fx file loading / parsing in D3D11. In D3D9, loading an entire effect file was D3DXCreateEffectFromFile( .. ), and you got a ID3DXEffect9, which had great methods like SetTechnique and BeginPass, making it easy to load and execute a shader with multiple techniques. Is this completely manual now in D3D11? The highest level functionality I can find is loading a SINGLE shader from an FX file using D3DX11CompileFromFile. Does anyone know if there's an easier way to load FX files and choose a technique? With the level of functionality provided in D3D11 now, it seems like you're better off just writing .hlsl files and forgetting about the whole idea of Techniques.

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• How to translate along Z axis in OpenTK

  - by JeremyJAlpha

  I am playing around with an OpenGL sample application I downloaded for Xamarin-Android. The sample application produces a rotating colored cube I would simply like to edit it so that the rotating cube is translated along the Z axis and disappears into the distance. I modified the code by: adding an cumulative variable to store my Z distance, adding GL.Enable(All.DepthBufferBit) - unsure if I put it in the right place, adding GL.Translate(0.0f, 0.0f, Depth) - before the rotate functions, Result: cube rotates a couple of times then disappears, it seems to be getting clipped out of the frustum. So my question is what is the correct way to use and initialize the Z buffer and get the cube to travel along the Z axis? I am sure I am missing some function calls but am unsure of what they are and where to put them. I apologise in advance as this is very basic stuff but am still learning :P, I would appreciate it if anyone could show me the best way to get the cube to still rotate but to also move along the Z axis. I have commented all my modifications in the code: // This gets called when the drawing surface is ready protected override void OnLoad (EventArgs e) { // this call is optional, and meant to raise delegates // in case any are registered base.OnLoad (e); // UpdateFrame and RenderFrame are called // by the render loop. This is takes effect // when we use 'Run ()', like below UpdateFrame += delegate (object sender, FrameEventArgs args) { // Rotate at a constant speed for (int i = 0; i < 3; i ++) rot [i] += (float) (rateOfRotationPS [i] * args.Time); }; RenderFrame += delegate { RenderCube (); }; GL.Enable(All.DepthBufferBit); //Added by Noob GL.Enable(All.CullFace); GL.ShadeModel(All.Smooth); GL.Hint(All.PerspectiveCorrectionHint, All.Nicest); // Run the render loop Run (30); } void RenderCube () { GL.Viewport(0, 0, viewportWidth, viewportHeight); GL.MatrixMode (All.Projection); GL.LoadIdentity (); if ( viewportWidth > viewportHeight ) { GL.Ortho(-1.5f, 1.5f, 1.0f, -1.0f, -1.0f, 1.0f); } else { GL.Ortho(-1.0f, 1.0f, -1.5f, 1.5f, -1.0f, 1.0f); } GL.MatrixMode (All.Modelview); GL.LoadIdentity (); Depth -= 0.02f; //Added by Noob GL.Translate(0.0f,0.0f,Depth); //Added by Noob GL.Rotate (rot[0], 1.0f, 0.0f, 0.0f); GL.Rotate (rot[1], 0.0f, 1.0f, 0.0f); GL.Rotate (rot[2], 0.0f, 1.0f, 0.0f); GL.ClearColor (0, 0, 0, 1.0f); GL.Clear (ClearBufferMask.ColorBufferBit); GL.VertexPointer(3, All.Float, 0, cube); GL.EnableClientState (All.VertexArray); GL.ColorPointer (4, All.Float, 0, cubeColors); GL.EnableClientState (All.ColorArray); GL.DrawElements(All.Triangles, 36, All.UnsignedByte, triangles); SwapBuffers (); }

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• Using Appendbuffers in unity for terrain generation

  - by Wardy

  Like many others I figured I would try and make the most of the monster processing power of the GPU but I'm having trouble getting the basics in place. CPU code: using UnityEngine; using System.Collections; public class Test : MonoBehaviour { public ComputeShader Generator; public MeshTopology Topology; void OnEnable() { var computedMeshPoints = ComputeMesh(); CreateMeshFrom(computedMeshPoints); } private Vector3[] ComputeMesh() { var size = (32*32) * 4; // 4 points added for each x,z pos var buffer = new ComputeBuffer(size, 12, ComputeBufferType.Append); Generator.SetBuffer(0, "vertexBuffer", buffer); Generator.Dispatch(0, 1, 1, 1); var results = new Vector3[size]; buffer.GetData(results); buffer.Dispose(); return results; } private void CreateMeshFrom(Vector3[] generatedPoints) { var filter = GetComponent<MeshFilter>(); var renderer = GetComponent<MeshRenderer>(); if (generatedPoints.Length > 0) { var mesh = new Mesh { vertices = generatedPoints }; var colors = new Color[generatedPoints.Length]; var indices = new int[generatedPoints.Length]; //TODO: build this different based on topology of the mesh being generated for (int i = 0; i < indices.Length; i++) { indices[i] = i; colors[i] = Color.blue; } mesh.SetIndices(indices, Topology, 0); mesh.colors = colors; mesh.RecalculateNormals(); mesh.Optimize(); mesh.RecalculateBounds(); filter.sharedMesh = mesh; } else { filter.sharedMesh = null; } } } GPU code: #pragma kernel Generate AppendStructuredBuffer<float3> vertexBuffer : register(u0); void genVertsAt(uint2 xzPos) { //TODO: put some height generation code here. // could even run marching cubes / dual contouring code. float3 corner1 = float3( xzPos[0], 0, xzPos[1] ); float3 corner2 = float3( xzPos[0] + 1, 0, xzPos[1] ); float3 corner3 = float3( xzPos[0], 0, xzPos[1] + 1); float3 corner4 = float3( xzPos[0] + 1, 0, xzPos[1] + 1 ); vertexBuffer.Append(corner1); vertexBuffer.Append(corner2); vertexBuffer.Append(corner3); vertexBuffer.Append(corner4); } [numthreads(32, 1, 32)] void Generate (uint3 threadId : SV_GroupThreadID, uint3 groupId : SV_GroupID) { uint2 currentXZ = unint2( groupId.x * 32 + threadId.x, groupId.z * 32 + threadId.z); genVertsAt(currentXZ); } Can anyone explain why when I call "buffer.GetData(results);" on the CPU after the compute dispatch call my buffer is full of Vector3(0,0,0), I'm not expecting any y values yet but I would expect a bunch of thread indexes in the x,z values for the Vector3 array. I'm not getting any errors in any of this code which suggests it's correct syntax-wise but maybe the issue is a logical bug. Also: Yes, I know I'm generating 4,000 Vector3's and then basically round tripping them. However, the purpose of this code is purely to learn how round tripping works between CPU and GPU in Unity.

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• How can I downsample a texture using FBOs?

  - by snape

  I am rendering a scene to FBO as my render target whose size is 8 times the size of the orignal screen in OpenGL. Now i wan to downsample the texture generated by FBO to the size of the screen so as to achieve spatial anti aliasing. How do i achieve the down sampling ? Please provide implementation details. Note : If there is a better way of doing anti aliasing in FBOs please mention that too. I am trying to remove the aliasing in the image attached below.

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• OpenGL position from depth is wrong

  - by CoffeeandCode

  My engine is currently implemented using a deferred rendering technique, and today I decided to change it up a bit. First I was storing 5 textures as so: DEPTH24_STENCIL8 - Depth and stencil RGBA32F - Position RGBA10_A2 - Normals RGBA8 x 2 - Specular & Diffuse I decided to minimize it and reconstruct positions from the depth buffer. Trying to figure out what is wrong with my method currently has not been fun :/ Currently I get this: which changes whenever I move the camera... weird Vertex shader really simple #version 150 layout(location = 0) in vec3 position; layout(location = 1) in vec2 uv; out vec2 uv_f; void main(){ uv_f = uv; gl_Position = vec4(position, 1.0); } Fragment shader Where the fun (and not so fun) stuff happens #version 150 uniform sampler2D depth_tex; uniform sampler2D normal_tex; uniform sampler2D diffuse_tex; uniform sampler2D specular_tex; uniform mat4 inv_proj_mat; uniform vec2 nearz_farz; in vec2 uv_f; ... other uniforms and such ... layout(location = 3) out vec4 PostProcess; vec3 reconstruct_pos(){ float z = texture(depth_tex, uv_f).x; vec4 sPos = vec4(uv_f * 2.0 - 1.0, z, 1.0); sPos = inv_proj_mat * sPos; return (sPos.xyz / sPos.w); } void main(){ vec3 pos = reconstruct_pos(); vec3 normal = texture(normal_tex, uv_f).rgb; vec3 diffuse = texture(diffuse_tex, uv_f).rgb; vec4 specular = texture(specular_tex, uv_f); ... do lighting ... PostProcess = vec4(pos, 1.0); // Just for testing } Rendering code probably nothing wrong here, seeing as though it always worked before this->gbuffer->bind(); gl::Clear(gl::COLOR_BUFFER_BIT | gl::DEPTH_BUFFER_BIT); gl::Enable(gl::DEPTH_TEST); gl::Enable(gl::CULL_FACE); ... bind geometry shader and draw models and shiz ... gl::Disable(gl::DEPTH_TEST); gl::Disable(gl::CULL_FACE); gl::Enable(gl::BLEND); ... bind textures and lighting shaders shown above then draw each light ... gl::BindFramebuffer(gl::FRAMEBUFFER, 0); gl::Clear(gl::COLOR_BUFFER_BIT | gl::DEPTH_BUFFER_BIT); gl::Disable(gl::BLEND); ... bind screen shaders and draw quad with PostProcess texture ... Rinse_and_repeat(); // not actually a function ;) Why are my positions being output like they are?

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• sprite animation system height recalculating has some issues

  - by Nicolas Martel

  Basically, the way it works is that it update the frame to show every let's say 24 ticks and every time the frame update, it recalculates the height and width of the new sprite to render so that my gravity logics and stuff works well. But the problem i am having now is a bit hard to explain in words only, therefore i will use this picture to assist me The picture So what i need basically is that if let's say i froze the sprite at the first frame, then unfreeze it and freeze it at the second frame, have the second frame's sprite (let's say it's a prone move) simply stand on the foothold without starting the gravity and when switching back, have the first sprite go back on the foothold like normal without being under the foothold. I had 2 ideas on doing this but I'm not sure it's the most efficient ways to do it so i wanna hear your inputs.

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• Explicit resource loading in Ogre (Mogre)

  - by sebf

  I am just starting to learn Mogre and what I would like to do is to be able to load resources 'explicitly' (i.e. I just provide an absolute path instead of using a resource group tied to a directory). This is very different to manually loading resources, which I believe in Ogre has a very specific meaning, to build up the object using Ogres methods. I want to use Ogres resource management system/resource loading code, but to have finer control over which files are loaded and in what groups they are. I remember reading how to do this but cannot find the page again; I think its possible to do something like: Declare a resource group Declare the resource(s) (this is when the actual resource file name is provided) Initialise the resource group to actually load the resource(s) Is this the correct procedure? If so, is there any example code showing how to do this?

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• WIn API Basic Paint program

  - by Tom Burman

  Just trying to learn a bit of Win API. Im trying to make a basic drawing app, a bit like MS Paint. For the time being im trying to get one function to work which is, when you left click and drag the mouse around the screen a line is drawn behind the mouse. Heres what i have so far, but for some reason: 1) the line starts drawing straight away rather then waiting for the left click 2) the line isn't solid its very dotty. case WM_MOUSEMOVE: { if(MK_LBUTTON){ hdc = GetDC(hwnd); hPen = CreatePen(PS_SOLID,5,RGB(0, 0, 255)); SelectObject(hdc, hPen); int x = LOWORD(lParam); int y = HIWORD(lParam); MoveToEx(hdc,x,y,NULL); LineTo(hdc, LOWORD(lParam), HIWORD(lParam)); ReleaseDC(hwnd,hdc); } else break; } } Thanks for any help!

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• OpenGLES GLSL Shader attributes always bound to 0

  - by codemonkey

  So I have a very simple vertex shader as follows #version 120 attribute vec3 position; attribute vec3 inColor; uniform mat4 mvp; varying vec3 fragColor; void main(void){ fragColor = inColor; gl_Position = mvp * vec4(position, 1.0); } Which I load, as well as the fragment shader: #version 120 varying vec3 fragColor; void main(void) { gl_FragColor = vec4(fragColor,1.0); } Which I then load, compile, and link to my shader program. I check for link status using glGetProgramiv(shaderProgram, GL_LINK_STATUS, &shaderSuccess); which returns GL_TRUE so I think its ok. However, when I query the active attributes and uniforms using #ifdef DEBUG int totalAttributes = -1; glGetProgramiv(shaderProgram, GL_ACTIVE_ATTRIBUTES, &totalAttributes); for(int i=0; i<totalAttributes; ++i) { int name_len=-1, num=-1; GLenum type = GL_ZERO; char name[100]; glGetActiveAttrib(shaderProgram, GLuint(i), sizeof(name)-1, &name_len, &num, &type, name ); name[name_len] = 0; GLuint location = glGetAttribLocation(shaderProgram, name); fprintf(stderr, "Attribute %s is bound at %d\n", name, location); } int totalUniforms = -1; glGetProgramiv(shaderProgram, GL_ACTIVE_UNIFORMS, &totalUniforms); for(int i=0; i<totalUniforms; ++i) { int name_len=-1, num=-1; GLenum type = GL_ZERO; char name[100]; glGetActiveUniform(shaderProgram, GLuint(i), sizeof(name)-1, &name_len, &num, &type, name ); name[name_len] = 0; GLuint location = glGetUniformLocation(shaderProgram, name); fprintf(stderr, "Uniform %s is bound at %d\n", name, location); } #endif I get: Attribute inColor is bound at 0 Attribute position is bound at 1 Uniform mvp is bound at 0 Which leads to failure when trying to use the shader to render the objects. I have tried switching the order of declaration of position & inColor, but still, only position is bound with the other two giving 0 Can someone please explain why this is happening? Thanks

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• Ray Tracing concers: Efficient Data Structure and Photon Mapping

  - by Grieverheart

  I'm trying to build a simple ray tracer for specific target scenes. An example of such scene can be seen below. I'm concerned as to what accelerating data structure would be most efficient in this case since all objects are touching but on the other hand, the scene is uniform. The objects in my ray tracer are stored as a collection of triangles, thus I also have access to individual triangles. Also, when trying to find the bounding box of the scene, how should infinite planes be handled? Should one instead use the viewing frustum to calculate the bounding box? A few other questions I have are about photon mapping. I've read the original paper by Jensen and many more material. In the compact data structure for the photon they introduce, they store photon power as 4 chars, which from my understanding is 3 chars for color and 1 for flux. But I don't understand how 1 char is enough to store a flux of the order of 1/n, where n is the number of photons (I'm also a bit confused about flux vs power). The other question about photon mapping is, if it would be more efficient in my case to store photons per object (or even per Object's triangle) instead of using a balanced kd-tree. Also, same question about bounding box of the scene but for photon mapping. How should one find a bounding box from the pov of the light when infinite planes are involved?

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• 2d Ice movement

  - by Jeremy Clarkson

  I am building an top-down 2d RPG like zelda. I have been trying to implement ice sliding. I have a tile with the slide property. I thought it would be easy to get working. I figured that I would read the slide property, and move the character forward until the slide property no longer exists. So I tried a loop but all it did was stop at the first tile in an infinite loop. I then took the loop out and tried taking direct control of the character to move him along the slide path but I couldn't get it to move. Is there an easy way to do an ice sliding tile based movement in libgdx. I looked for a tutorial but none exist.

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• How to snap a 2D Quad to the mouse cursor using OpenGL 3.0/WIN32?

  - by NoobScratcher

  I've been having issues trying to snap a 2D Quad to the mouse cursor position I'm able : 1.) To get values into posX, posY, posZ 2.) Translate with the values from those 3 variables But the quad positioning I'm not able to do correctly in such a way that the 2D Quad is near the mouse cursor using those values from those 3 variables eg."posX, posY, posZ" I need the mouse cursor in the center of the 2D Quad. I'm hoping someone can help me achieve this. I've tried searching around with no avail. Heres the function that is ment to do the snapping but instead creates weird flicker or shows nothing at all only the 3d models show up : void display() { glClearColor(0.0,0.0,0.0,1.0); glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT); for(std::vector<GLuint>::iterator I = cube.begin(); I != cube.end(); ++I) { glCallList(*I); } if(DrawArea == true) { glReadPixels(winX, winY, 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &winZ); cerr << winZ << endl; glGetDoublev(GL_MODELVIEW_MATRIX, modelview); glGetDoublev(GL_PROJECTION_MATRIX, projection); glGetIntegerv(GL_VIEWPORT, viewport); gluUnProject(winX, winY, winZ , modelview, projection, viewport, &posX, &posY, & posZ); glBindTexture(GL_TEXTURE_2D, DrawAreaTexture); glPixelStorei(GL_UNPACK_ALIGNMENT, 1); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL); glTexImage2D (GL_TEXTURE_2D, 0, GL_RGB, DrawAreaSurface->w, DrawAreaSurface->h, 0, GL_RGBA, GL_UNSIGNED_BYTE, DrawAreaSurface->pixels); glEnable(GL_TEXTURE_2D); glBindTexture(GL_TEXTURE_2D, DrawAreaTexture); glTranslatef(posX , posY, posZ); glBegin(GL_QUADS); glTexCoord2f (0.0, 0.0); glVertex3f(0.5, 0.5, 0); glTexCoord2f (1.0, 0.0); glVertex3f(0, 0.5, 0); glTexCoord2f (1.0, 1.0); glVertex3f(0, 0, 0); glTexCoord2f (0.0, 1.0); glVertex3f(0.5, 0, 0); glEnd(); } SwapBuffers(hDC); } I'm using : OpenGL 3.0 WIN32 API C++ GLSL if you really want the full source here it is - http://pastebin.com/1Ncm9HNf , Its pretty messy.

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• Android : glowing/pulsing line/triangle

  - by AndroidGecko

  I would like to create a simple Android app using Opengl ES 2.0 that is showing a simple shape (like line or triangle) that is glowing and pulsing like Nexus X logo in this video : http://youtu.be/jBKVAfZUFqI?t=59s What should I look for? So far I googled around for glowing effects and found techniques like "bloom" or "additive blending". Are they relevant here? how I would implement pulsing glow with them? Any links to relevant works very appreciated Thanks! P.S - I am very familiar with Android SDK; just started with OpenGL ES

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• Hardware instancing for voxel engine

  - by Menno Gouw

  i just did the tutorial on Hardware Instancing from this source: http://www.float4x4.net/index.php/2011/07/hardware-instancing-for-pc-in-xna-4-with-textures/. Somewhere between 900.000 and 1.000.000 draw calls for the cube i get this error "XNA Framework HiDef profile supports a maximum VertexBuffer size of 67108863." while still running smoothly on 900k. That is slightly less then 100x100x100 which are a exactly a million. Now i have seen voxel engines with very "tiny" voxels, you easily get to 1.000.000 cubes in view with rough terrain and a decent far plane. Obviously i can optimize a lot in the geometry buffer method, like rendering only visible faces of a cube or using larger faces covering multiple cubes if the area is flat. But is a vertex buffer of roughly 67mb the max i can work with or can i create multiple?

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• Implementing top view physics using box2D

  - by humbleBee

  How can top view physics games be done in box2D? One idea I have is to set the linear velocity of an object manually or to alter the linear and angular damping as my object moves over different surfaces. For example if my object is over a wet surface it'll have less linear damping and if it is over rough surface it'll have more damping. And to see if my object has fallen over an edge I'll try to use an AABB and check if its still inside or manually see if object.x > boundary.x etc. Is there any better way?

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• Efficiently representing a dynamic transform hierarchy

  - by Mattia

  I'm looking for a way to represent a dynamic transform hierarchy (i.e. one where nodes can be inserted and removed arbitrarily) that's a bit more efficient than using a standard tree of pointers . I saw the answers to this question ( Efficient structure for representing a transform hierarchy. ), but as far as I can determine the tree-as-array approach only works for static hierarchies or dynamic ones where nodes have a fixed number of children (both deal-breakers for me). I'm probably wrong about that but could anyone point out how? If I'm not wrong are there other alternatives that work for dynamic hierarchies?

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• Getting the number of fragments which passed the depth test

  - by Etan

  In "modern" environments, the "NV Occlusion Query" extension provides a method to get the number of fragments which passed the depth test. However, on the iPad / iPhone using OpenGL ES, the extension is not available. What is the most performant approach to implement a similar behaviour in the fragment shader? Some of my ideas: Render the object completely in white, then count all the colors together using a two-pass shader where first a vertical line is rendered and for each fragment the shader computes the sum over the whole row. Then, a single vertex is rendered whose fragment sums all the partial sums of the first pass. Doesn't seem to be very efficient. Render the object completely in white over a black background. Downsample recursively, abusing the hardware linear interpolation between textures until being at a reasonably small resolution. This leads to fragments which have a greyscale level depending on the number of white pixels where in their corresponding region. Is this even accurate enough? Use mipmaps and simply read the pixel on the 1x1 level. Again the question of accuracy and if it is even possible using non-power-of-two textures. The problem wit these approaches is, that the pipeline gets stalled which results in major performance issues. Therefore, I'm looking for a more performant way to accomplish my goal. Using the EXT_OCCLUSION_QUERY_BOOLEAN extension Apple introduced EXT_OCCLUSION_QUERY_BOOLEAN in iOS 5.0 for iPad 2. "4.1.6 Occlusion Queries Occlusion queries use query objects to track the number of fragments or samples that pass the depth test. An occlusion query can be started and finished by calling BeginQueryEXT and EndQueryEXT, respectively, with a target of ANY_SAMPLES_PASSED_EXT or ANY_SAMPLES_PASSED_CONSERVATIVE_EXT. When an occlusion query is started with the target ANY_SAMPLES_PASSED_EXT, the samples-boolean state maintained by the GL is set to FALSE. While that occlusion query is active, the samples-boolean state is set to TRUE if any fragment or sample passes the depth test. When the occlusion query finishes, the samples-boolean state of FALSE or TRUE is written to the corresponding query object as the query result value, and the query result for that object is marked as available. If the target of the query is ANY_SAMPLES_PASSED_CONSERVATIVE_EXT, an implementation may choose to use a less precise version of the test which can additionally set the samples-boolean state to TRUE in some other implementation dependent cases." The first sentence hints on a behavior which is exactly what I'm looking for: getting the number of pixels which passed the depth test in an asynchronous manner without much performance loss. However, the rest of the document describes only how to get boolean results. Is it possible to exploit this extension to get the pixel count? Does the hardware support it so that there may be hidden API to get access to the pixel count? Other extensions which could be exploitable would be debugging features like the number of times the fragment shader was invoked (PSInvocations in DirectX - not sure if something simila is available in OpenGL ES). However, this would also result in a pipeline stall.

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• Drawing a random x,y grid of objects within a prespective

  - by T Reddy

  I'm wrapping my head around OpenGL ES 2.0 and I think I'm trying to do something very simple, but I think the math may be eluding me. I created a simple, flat-ish cylinder in Blender that is 2 units in diameter. I want to create an arbitrary grid of these edge to edge (think of a checker board). I'm using a 3D perspective with GLKit: CGSize size = [[self view] bounds].size; _projectionMatrix = GLKMatrix4MakePerspective(GLKMathDegreesToRadians(45.0f), size.width/size.height, 0.1f, 100.0f); So, I managed to manually get all of these cylinders drawn on the screen just fine. However, I would like to understand how I can programmatically "fit" all of these cylinders on the screen at the same time given the camera location, screen size, cylinder diameter, and the number of rows/columns. So the net effect is that for small grids (i.e., 5x5) the objects are closer to the camera, but for large grids (i.e., 30x30) the objects are farther away. In either case, all of the cylinders are visible.

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• Sharing VBO with multiple objects and fixed size buffer data

  - by Mark Ingram

  I'm just messing around with OpenGL and getting some basic structures in place and my first attempt resulted in each SceneObject class (just contains vertex information right now) having it's own VBO inside it, however I've read that it might be better to share VBOs across multiple objects. Also, I read that you should avoid resizing a VBO (repeated calls to glBufferData with different size parameters), and instead choose a fixed size for a VBO, and just try a range from the buffer. I don't think changing the size of the buffer data would happen too often, but surely it would be better to only allocate the data you need? Choosing an arbitrary value seems risky. I'm looking for some advice on working with individual objects in a scene and their associated buffer data.

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• OpenGL ES Loading

  - by kuroutadori

  I want to know what is the norm of loading rendering code. Take a button. When the application is loaded, a texture is loaded which has the image of the button on it. When the button is tapped, it then adds a loader into a queue, which is loaded on render thread. It then loads up an array buffer with vertexes and tex coords when render is called. It then adds to a render tree. Then it renders. the render function looks like this void render() { update(); mBaseRenderer->render(); } update() is when the queue is checked to see if anything needs loading. mBaseRenderer->render() is the render tree. What I am asking then is, should I even have the update() there at all and instead have everything preloaded before it renders? If I can have it loaded when need, for instance when there is tap, then how can it be done (My current code causes an dequeueing buffer error (Unknown error: -75) which I assume is to do with OpenGL ES and the context)?

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• Masking OpenGL texture by a pattern

  - by user1304844

  Tiled terrain. User wants to build a structure. He presses build and for each tile there is an "allow" or "disallow" tile sprite added to the scene. FPS drops right away, since there are 600+ tiles added to the screen. Since map equals screen, there is no scrolling. I came to an idea to make an allow grid covering the whole map and mask the disallow fields. Approach 1: Create allow and disallow grid textures. Draw a polygon on screen. Pass both textures to the fragment shader. Determine the position inside the polygon and use color from allowTexture if the fragment belongs to the allow field, disallow otherwise Problem: How do I know if I'm on the field that isn't allowed if I cannot pass the matrix representing the map (enum FieldStatus[][] (Allow / Disallow)) to the shader? Therefore, inside the shader I don't know which fragments should be masked. Approach 2: Create allow texture. Create an empty texture buffer same size as the allow texture Memset the pixels of the empty texture to desired color for each pixel that doesn't allow building. Draw a polygon on screen. Pass both textures to the fragment shader. Use texture2 color if alpha 0, texture1 color otherwise. Problem: I'm not sure what is the right way to manipulate pixels on a texture. Do I just make a buffer with width*height*4 size and memcpy the color[] to desired coordinates or is there anything else to it? Would I have to call glTexImage2D after every change to the texture? Another problem with this approach is that it takes a lot more work to get a prettier effect since I'm manipulating the color pixels instead of just masking two textures. varying vec2 TexCoordOut; uniform sampler2D Texture1; uniform sampler2D Texture2; void main(void){ vec4 allowColor = texture2D(Texture1, TexCoordOut); vec4 disallowColor = texture2D(Texture2, TexCoordOut); if(disallowColor.a > 0){ gl_FragColor= disallowColor; }else{ gl_FragColor= allowColor; }} I'm working with OpenGL on Windows. Any other suggestion is welcome.

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• Correct use of VAO's in OpenGL ES2 for iOS?

  - by sak

  I'm migrating to OpenGL ES2 for one of my iOS projects, and I'm having trouble to get any geometry to render successfully. Here's where I'm setting up the VAO rendering: void bindVAO(int vertexCount, struct Vertex* vertexData, GLushort* indexData, GLuint* vaoId, GLuint* indexId){ //generate the VAO & bind glGenVertexArraysOES(1, vaoId); glBindVertexArrayOES(*vaoId); GLuint positionBufferId; //generate the VBO & bind glGenBuffers(1, &positionBufferId); glBindBuffer(GL_ARRAY_BUFFER, positionBufferId); //populate the buffer data glBufferData(GL_ARRAY_BUFFER, vertexCount, vertexData, GL_STATIC_DRAW); //size of verte position GLsizei posTypeSize = sizeof(kPositionVertexType); glVertexAttribPointer(kVertexPositionAttributeLocation, kVertexSize, kPositionVertexTypeEnum, GL_FALSE, sizeof(struct Vertex), (void*)offsetof(struct Vertex, position)); glEnableVertexAttribArray(kVertexPositionAttributeLocation); //create & bind index information glGenBuffers(1, indexId); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, *indexId); glBufferData(GL_ELEMENT_ARRAY_BUFFER, vertexCount, indexData, GL_STATIC_DRAW); //restore default state glBindVertexArrayOES(0); glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0); glBindBuffer(GL_ARRAY_BUFFER, 0); } And here's the rendering step: //bind the frame buffer for drawing glBindFramebuffer(GL_FRAMEBUFFER, outputFrameBuffer); glClear(GL_COLOR_BUFFER_BIT); //use the shader program glUseProgram(program); glClearColor(0.4, 0.5, 0.6, 0.5); float aspect = fabsf(320.0 / 480.0); GLKMatrix4 projectionMatrix = GLKMatrix4MakePerspective(GLKMathDegreesToRadians(65.0f), aspect, 0.1f, 100.0f); GLKMatrix4 modelViewMatrix = GLKMatrix4MakeTranslation(0.0f, 0.0f, -1.0f); GLKMatrix4 mvpMatrix = GLKMatrix4Multiply(projectionMatrix, modelViewMatrix); //glUniformMatrix4fv(projectionMatrixUniformLocation, 1, GL_FALSE, projectionMatrix.m); glUniformMatrix4fv(modelViewMatrixUniformLocation, 1, GL_FALSE, mvpMatrix.m); glBindVertexArrayOES(vaoId); glDrawElements(GL_TRIANGLE_FAN, kVertexCount, GL_FLOAT, &indexId); //bind the color buffer glBindRenderbuffer(GL_RENDERBUFFER, colorRenderBuffer); [context presentRenderbuffer:GL_RENDERBUFFER]; The screen is rendering the color passed to glClearColor correctly, but not the shape passed into bindVAO. Is my VAO being built correctly? Thanks!

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