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• why is glVertexAttribDivisor crashing?

  - by 2am

  I am trying to render some trees with instancing. This is rather weird, but before sleeping yesterday night, I checked the code, and it was in a running state, when I got up this morning, it is crashing when I am calling glVertexAttribDivisor I haven't changed any code since yesterday. Here is how I am sending data to GPU for instancing. glGenBuffers(1, &iVBO); glBindBuffer(GL_ARRAY_BUFFER, iVBO); glBufferData(GL_ARRAY_BUFFER, (ml_instance->i_positions.size()*sizeof(glm::vec4)) , NULL, GL_STATIC_DRAW); glBufferSubData(GL_ARRAY_BUFFER, 0, (ml_instance->i_positions.size()*sizeof(glm::vec4)), &ml_instance->i_positions[0]); And then in vertex specification-- glBindBuffer(GL_ARRAY_BUFFER, iVBO); glVertexAttribPointer(i_positions, 4, GL_FLOAT, GL_FALSE, 0, 0); glEnableVertexAttribArray(i_positions); glVertexAttribDivisor(i_positions,1); // **THIS IS WHERE THE PROGRAM CRASHES** glDrawElementsInstanced(GL_TRIANGLES, indices.size(), GL_UNSIGNED_INT, 0,TREES_INSTANCE_COUNT); I have checked ml_instance->i_positions, it has all the data that needs to render. I have checked the value of i_positions in vertex shader, it is the same as whatever I have defined there. I am little out of ideas here, everything looks pretty much fine. What am I missing?

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• How do I render only part of a texture to a point sprite in OpenGL ES for Android?

  - by nbolton

  Using the libgdx framework, I've figured out how to render a texture to a point sprite. The problem is, it renders the entire texture to the point sprite, where I only want a small part of it (since it's an isometric tile image). Here's a snippet from some demo code I wrote... create() { renderer = new ImmediateModeRenderer(); tiles = Gdx.graphics.newTexture( Gdx.files.internal("data/tiles2.png"), TextureFilter.MipMap, TextureFilter.Linear, TextureWrap.ClampToEdge, TextureWrap.ClampToEdge); Gdx.gl.glClearColor(0.6f, 0.7f, 0.9f, 1); Gdx.gl.glEnable(GL10.GL_TEXTURE_2D); Gdx.gl.glEnable(GL11.GL_POINT_SPRITE_OES); Gdx.gl11.glTexEnvi( GL11.GL_POINT_SPRITE_OES, GL11.GL_COORD_REPLACE_OES, GL11.GL_TRUE); Gdx.gl10.glPointSize(s); tiles.bind(); } render() { Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT); renderer.begin(GL10.GL_POINTS); // render 3 point sprites at various 3d points renderer.vertex(-.1f, 0, -.1f); renderer.vertex(0, 0, 0); renderer.vertex(.1f, 0, .1f); // ... more vertices here if needed (one for each sprite) ... renderer.end(); }

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• Precision loss when transforming from cartesian to isometric

  - by Justin Skiles

  My goal is to display a tile map in isometric projection. This tile map has 25 tiles across and 25 tiles down. Each tile is 32x32. See below for how I'm accomplishing this. World Space World Space to Screen Space Rotation (45 degrees) Using a 2D rotation matrix, I use the following: double rotation = Math.PI / 4; double rotatedX = ((tileWorldX * Math.Cos(rotation)) - ((tileWorldY * Math.Sin(rotation))); double rotatedY = ((tileWorldX * Math.Sin(rotation)) + (tileWorldY * Math.Cos(rotation))); World Space to Screen Space Scale (Y-axis reduced by 50%) Here I simply scale down the Y value by a factor of 0.5. Problem And it works, kind of. There are some tiny 1px-2px gaps between some of the tiles when rendering. I think there's some precision loss somewhere, or I'm not understanding how to get these tiles to fit together perfectly. I'm not truncating or converting my values to non-decimal types until I absolutely have to (when I pass to the render method, which only takes integers). I'm not sure how to guarantee pixel perfect rendering precision when I'm rotating and scaling on a level of higher precision. Any advice? Do I need to supply for information?

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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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• Consistency of DirectX models

  - by marc wellman

  Is there a way to check the consistency of a DirectX model (.x) ? Whilst compiling .x files with XNA GameStudio 3.1 compilation is aborted with the following error message: Error 2 Could not read the X file. The file is corrupt or invalid. Error code: D3DXFERR_PARSEERROR. C:\WFP\Browser\Content\m.x KiviBrowser Some models compile correctly without any error/warning and some abort as described. The files of each model have several thousand lines. I am creating the files in Googles SketchUp 8 where they all look fine and don't show any sign of corruption. Suppose I have such a model my XNA compiler won't compile because their is an inconsistency somewhere in the file - how could I identify this in order to correct it ?

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• How can I determine if a cube is adjacent to another cube, and optimize its buffers if so?

  - by Christian Frantz

  I'm trying to optimize the rendering of a collection of cubes, (based on an answer I was given to another question I asked). I understand the logic behind occlusion culling, but I'm having trouble with the code. When I create a cube, I want to determine if that cube is touching another existing cube, and if so I don't want to generate the redundant data in my vertex or index buffers. I'm planning on making a method that I call from my cube constructor so that everytime I create a cube, these checks are made, and neither occluded face is ever drawn. How would I go about this?

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• What calls trigger a new batch?

  - by sebf

  I am finding my project is starting to show performance degradation and I need to optimize it. The answer to my previous question and this presentation from NVidia have helped greatly in understanding the performance characteristics of code using the GPU but there are a couple of things that aren't clear that I need to know to optimize my drawing. Specifically, what calls make the distinction between batches. I know that any state changes cause a new batch, so that includes: Render State Changes Buffer Changes Shader Changes Render Target Changes Correct? What else counts as a 'state change'? Does each Draw**Primitive() call constitute a new batch? Even if I were to issue the same call twice, with no state changes, or call it once on on part of the buffer, then again on another? If I were to update a buffer, but not change the bindings, would that be a new batch? That presentation and a DX9 page suggest using all of the texture slots available, which I take to mean loading multiple objects in 'parallel' by mapping their buffers/shaders/textures to slots 1-16. But I am not sure how this works - surely to do this you would need to change the buffer binding and that would count as a state change? (or is it a case of you do but it saves 16 calls so its OK?)

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• HedgeWar code confusion

  - by BluFire

  I looked at an open source project(HedgeWars) that was built using many programming languages such as C++ and Java. While I was looking through the code, I couldn't help noticing that all the math and physics were gone from the Java code. HedgeWars I imported the project file called "SDL-android-project" which was a sub folder to "android build" and project files. My question is where is all the math and physics inside the code? Do I have to look at the C++ code in order to see it? I think Hedgewars was originally programmed in C++ but the files are confusing be because of its size and the fact that it has several programming languages inside.

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• How to get warnings when compiling fx files

  - by jdv-Jan de Vaan

  When I compile DirectX shaders (.fx files), I dont see any compiler warnings unless there was an error in the effect. This happens both when using the offline FXC compiler, as well as calling SlimDx's CompileEffect (which is what we normally do). I could force warnings as errors (/WX), but if you enable that, you get an error that compilation failed, without the warning that caused the problem. So how can I output warnings for shaders that compile properly?

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• Complete Guide/Tutorials on LWJGL?

  - by user43353

  Dont get me wrong, I finished these tutorials on http://lwjgl.org/wiki/index.php?title=Main_Page. I finished The Basics section, OpenGL 3.2 and newer section, and I looked at the Example Code section. They were great tutorials, and I have looked at the external tutorials as well. I don't know where to go from here, and OpenGL is not my strong point. Some one suggested Learning Modern 3D Graphics Programming, and I didnt learn much. I looked at the port to LWJGL, but the book was on C and I couldn't really understand what the OpenGL meant. I am trying to learn 2D gaming, not 3D. Maybe later. Is there any tutorials that aren't C/C++ heavy and teach you 2D OpenGL?

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• libgdx arrays onTouch() method and delays for objects

  - by johnny-b

  i am trying to create random bullets but it is not working for some reason. also how can i make a delay so the bullets come every 30 seconds or 1 minute???? also the onTouch method does not work and it is not taking the bullet away???? shall i put the array in the GameRender class? thanks public class GameWorld { public static Ball ball; private Bullet bullet1; private ScrollHandler scroller; private Array<Bullet> bullets = new Array<Bullet>(); public GameWorld() { ball = new Ball(280, 273, 32, 32); bullet = new Bullet(-300, 200); scroller = new ScrollHandler(0); bullets.add(new Bullet(bullet.getX(), bullet.getY())); bullets = new Array<Bullet>(); Bullet bullet = null; float bulletX = 0.0f; float bulletY = 0.0f; for (int i=0; i < 10; i++) { bulletX = MathUtils.random(-10, 10); bulletY = MathUtils.random(-10, 10); bullet = new Bullet(bulletX, bulletY); bullets.add(bullet); } } 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 getBullet1() { return bullet1; } } i also tried this and it is not working, i used this in the GameRender class Array<Bullet> enemies=new Array<Bullet>(); //in the constructor of the class enemies.add(new Bullet(bullet.getX(), bullet.getY())); // this throws an exception for some reason??? this is in the render method for(int i=0; i<bullet.size; i++) bullet.get(i).draw(batcher); //this i am using in any method that will allow me from the constructor to update to render for(int i=0; i<bullet.size; i++) bullet.get(i).update(delta); this is not taking the bullet out @Override public boolean touchDown(int screenX, int screenY, int pointer, int button) { for(int i=0; i<bullet.size; i++) if(bullet.get(i).getBounds().contains(screenX,screenY)) bullet.removeIndex(i--); return false; } thanks for the help anyone.

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• How do GameEngines stop Pixel Seams appearing in adjacent mesh boundaries due to FP imprecision?

  - by ufomorace

  Graphics cards are mathematically imprecise. So when some meshes are joined by their borders, the graphics card often makes mistakes and decides that some pixels at the seam represent neither object, and unwanted pixels appear. It's a natural behaviour on all graphics cards. How are such worries avoided in Pro Games? Batching? Shaders? Different tangent vectors? Merging? Overlaping seams? Dark backgrounds? Extra vertices at borders? Z precision? Camera distance tweaks? Screencap of a fix that ended up not working:

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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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• Building View Matrix in Direct3D11

  - by Balls

  Am I doing it right? I converted this. m_ViewMatrix = XMMatrixLookAtLH(XMLoadFloat3(&m_Position), lookAtVector, upVector); to this one. XMVECTOR vz = XMVector3Normalize( lookAtVector - XMLoadFloat3(&m_Position) ); XMVECTOR vx = XMVector3Normalize( XMVector3Cross( upVector, vz ) ); XMVECTOR vy = XMVector3Cross( vz, vx ); m_ViewMatrix.r[0] = vx; m_ViewMatrix.r[1] = vy; m_ViewMatrix.r[2] = vz; m_ViewMatrix.r[3] = XMLoadFloat3(&m_Position); m_ViewMatrix.r[0].m128_f32[3] = 0.0f; m_ViewMatrix.r[1].m128_f32[3] = 0.0f; m_ViewMatrix.r[2].m128_f32[3] = 0.0f; m_ViewMatrix.r[3].m128_f32[3] = 1.0f; m_ViewMatrix = XMMatrixInverse( &XMMatrixDeterminant(m_ViewMatrix), m_ViewMatrix ); Everything looks fine when I run it. Another question is, I saw on this site(http://webglfactory.blogspot.com/2011/06/how-to-create-view-matrix.html) that he subtracted lookat from position in his vector vz. I tried it but gave me wrong view matrix. Can anyone check my code. I'm studying linear algebra right now. Sucks my course doesn't have one. Thank you, Balls

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• 3D rotation matrices deform object while rotating

  - by Kevin

  I'm writing a small 3D renderer (using an orthographic projection right now). I've run into some trouble with my 3D rotation matrices. They seem to squeeze my 3D object (a box primitive) at certain angles. Here's a live demo (only tested in Google Chrome): http://dl.dropbox.com/u/109400107/3D/index.html The box is viewed from the top along the Y axis and is rotating around the X and Z axis. These are my 3 rotation matrices (Only rX and rZ are being used): var rX = new Matrix([ [1, 0, 0], [0, Math.cos(radiants), -Math.sin(radiants)], [0, Math.sin(radiants), Math.cos(radiants)] ]); var rY = new Matrix([ [Math.cos(radiants), 0, Math.sin(radiants)], [0, 1, 0], [-Math.sin(radiants), 0, Math.cos(radiants)] ]); var rZ = new Matrix([ [Math.cos(radiants), -Math.sin(radiants), 0], [Math.sin(radiants), Math.cos(radiants), 0], [0, 0, 1] ]); Before projecting the verticies I multiply them by rZ and rX like so: vert1.multiply(rZ); vert1.multiply(rX); vert2.multiply(rZ); vert2.multiply(rX); vert3.multiply(rZ); vert3.multiply(rX); The projection itself looks like this: bX = (pos.x + (vert1.x*scale)); bY = (pos.y + (vert1.z*scale)); Where "pos.x" and "pos.y" is an offset for centering the box on the screen. I just can't seem to find a solution to this and I'm still relativly new to working with Matricies. You can view the source-code of the demo page if you want to see the whole thing.

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• Smooth pixels while rotating sprite

  - by goodm

  I just started with andengine, so this maybe gonna be silly question. How to make my sprites more smooth while I rotate them? Or maybe it because this is screenshot from tablet? Thanks JohnEye it works: Just need to change my BitmapTextureAtlas from: BitmapTextureAtlas carAtlas = new BitmapTextureAtlas(this.getTextureManager(),100, 63); to: BitmapTextureAtlas carAtlas = new BitmapTextureAtlas(this.getTextureManager(),100, 63, TextureOptions.BILINEAR);

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• Inverse projection: question about w coordinate

  - by fayeWilly

  I have to perform in shader an inverse projection from a u/v of a render target. What I do is: Get NDC as 2*(u,v,depth) - 1 Then world space as tmp = (P*V)^-1 * (NDC,1.0); world space = tmp/tmp.w; This apparently works, but I am confused about the w division there. Why this work? Shouldn't be a multiplication by a w somewhere (as in the "forward" pipeline there is the perpsective division?) Thank you, Faye

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• What would be a good filter to create 'magnetic deformers' from a depth map?

  - by sebf

  In my project, I am creating a system for deforming a highly detailed mesh (clothing) so that it 'fits' a convex mesh. To do this I use depth maps of the item and the 'hull' to determine at what point in world space the deviation occurs and the extent. Simply transforming all occluded vertices to the depths as defined by the 'hull' is fairly effective, and has good performance, but it suffers the problem of not preserving the features of the mesh and requires extensive culling to avoid false-positives. I would like instead to generate from the depth deviation map a set of simple 'deformers' which will 'push'* all vertices of the deformed mesh outwards (in world space). This way, all features of the mesh are preserved and there is no need to have complex heuristics to cull inappropriate vertices. I am not sure how to go about generating this deformer set however. I am imagining something like an algorithm that attempts to match a spherical surface to each patch of contiguous deviations within a certain range, but do not know where to start doing this. Can anyone suggest a suitable filter or algorithm for generating deformers? Or to put it another way 'compressing' a depth map? (*Push because its fitting to a convex 'bulgy' humanoid so transforms are likely to be 'spherical' from the POV of the surface.)

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• Quake 3 Bot Programming Example

  - by Manni

  I would like to implement an intelligent bot for Quake-3. I downloaded the and built the code successfully under Linux. My problem is that I couldn't find any complete tutorial telling me how to build an agent; telling which files to use( as there are many files in the source code). Can you give me a website or piece of source code telling me how to start? Or something like an example source code for a bot.

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• XNA texture stretching at extreme coordinates

  - by Shaun Hamman

  I was toying around with infinitely scrolling 2D textures using the XNA framework and came across a rather strange observation. Using the basic draw code: spriteBatch.Begin(SpriteSortMode.Deferred, null, SamplerState.PointWrap, null, null); spriteBatch.Draw(texture, Vector2.Zero, sourceRect, Color.White, 0.0f, Vector2.Zero, 2.0f, SpriteEffects.None, 1.0f); spriteBatch.End(); with a small 32x32 texture and a sourceRect defined as: sourceRect = new Rectangle(0, 0, Window.ClientBounds.Width, Window.ClientBounds.Height); I was able to scroll the texture across the window infinitely by changing the X and Y coordinates of the sourceRect. Playing with different coordinate locations, I noticed that if I made either of the coordinates too large, the texture no longer drew and was instead replaced by either a flat color or alternating bands of color. Tracing the coordinates back down, I found the following at around (0, -16,777,000): As you can see, the texture in the top half of the image is stretched vertically. My question is why is this occurring? Certainly I can do things like bind the x/y position to some low multiple of 32 to give the same effect without this occurring, so fixing it isn't an issue, but I'm curious about why this happens. My initial thought was perhaps it was overflowing the coordinate value or some such thing, but looking at a data type size chart, the next closest below is an unsigned short with a range of about 32,000, and above is an unsigned int with a range of around 2,000,000,000 so that isn't likely the cause.

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• Annoying flickering of vertices and edges (possible z-fighting)

  - by Belgin

  I'm trying to make a software z-buffer implementation, however, after I generate the z-buffer and proceed with the vertex culling, I get pretty severe discrepancies between the vertex depth and the depth of the buffer at their projected coordinates on the screen (i.e. zbuffer[v.xp][v.yp] != v.z, where xp and yp are the projected x and y coordinates of the vertex v), sometimes by a small fraction of a unit and sometimes by 2 or 3 units. Here's what I think is happening: Each triangle's data structure holds the plane's (that is defined by the triangle) coefficients (a, b, c, d) computed from its three vertices from their normal: void computeNormal(Vertex *v1, Vertex *v2, Vertex *v3, double *a, double *b, double *c) { double a1 = v1 -> x - v2 -> x; double a2 = v1 -> y - v2 -> y; double a3 = v1 -> z - v2 -> z; double b1 = v3 -> x - v2 -> x; double b2 = v3 -> y - v2 -> y; double b3 = v3 -> z - v2 -> z; *a = a2*b3 - a3*b2; *b = -(a1*b3 - a3*b1); *c = a1*b2 - a2*b1; } void computePlane(Poly *p) { double x = p -> verts[0] -> x; double y = p -> verts[0] -> y; double z = p -> verts[0] -> z; computeNormal(p -> verts[0], p -> verts[1], p -> verts[2], &p -> a, &p -> b, &p -> c); p -> d = p -> a * x + p -> b * y + p -> c * z; } The z-buffer just holds the smallest depth at the respective xy coordinate by somewhat casting rays to the polygon (I haven't quite got interpolation right yet so I'm using this slower method until I do) and determining the z coordinate from the reversed perspective projection formulas (which I got from here: double z = -(b*Ez*y + a*Ez*x - d*Ez)/(b*y + a*x + c*Ez - b*Ey - a*Ex); Where x and y are the pixel's coordinates on the screen; a, b, c, and d are the planes coefficients; Ex, Ey, and Ez are the eye's (camera's) coordinates. This last formula does not accurately give the exact vertices' z coordinate at their projected x and y coordinates on the screen, probably because of some floating point inaccuracy (i.e. I've seen it return something like 3.001 when the vertex's z-coordinate was actually 2.998). Here is the portion of code that hides the vertices that shouldn't be visible: for(i = 0; i < shape.nverts; ++i) { double dist = shape.verts[i].z; if(z_buffer[shape.verts[i].yp][shape.verts[i].xp].z < dist) shape.verts[i].visible = 0; else shape.verts[i].visible = 1; } How do I solve this issue? EDIT I've implemented the near and far planes of the frustum, with 24 bit accuracy, and now I have some questions: Is this what I have to do this in order to resolve the flickering? When I compare the z value of the vertex with the z value in the buffer, do I have to convert the z value of the vertex to z' using the formula, or do I convert the value in the buffer back to the original z, and how do I do that? What are some decent values for near and far? Thanks in advance.

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• Current state of the art for holographic displays?

  - by kamziro

  In another thread I was asking about independent arcade system development, and partly it was because I'm interested in using available 3D holographic technology for the displays. I saw one which involved a rotating mirror at very high speeds, so that's probably not going to be too feasible (I'd hate to think of what happens when something goes wrong). However, I looked around for videos from trade shows, and I found this: http://www.youtube.com/watch?v=Vl0EIngM-RA But information is scarce, and I'm led to believe it's just using mirrors and reflections, and does not convey true 3D depth like the one using rotating mirrors at high speed: http://www.youtube.com/watch?v=YKCUGQ-uo8c So yeah, does anyone know if there's something better available today?

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• Generate texture for a heightmap

  - by James

  I've recently been trying to blend multiple textures based on the height at different points in a heightmap. However i've been getting poor results. I decided to backtrack and just attempt to recreate one single texture from an SDL_Surface (i'm using SDL) and just send that into opengl. I'll put my code for creating the texture and reading the colour values. It is a 24bit TGA i'm loading, and i've confirmed that the rest of my code works because i was able to send the surfaces pixels directly to my createTextureFromData function and it drew fine. struct RGBColour { RGBColour() : r(0), g(0), b(0) {} RGBColour(unsigned char red, unsigned char green, unsigned char blue) : r(red), g(green), b(blue) {} unsigned char r; unsigned char g; unsigned char b; }; // main loading code SDLSurfaceReader* reader = new SDLSurfaceReader(m_renderer); reader->readSurface("images/grass.tga"); // new texture unsigned char* newTexture = new unsigned char[reader->m_surface->w * reader->m_surface->h * 3 * reader->m_surface->w]; for (int y = 0; y < reader->m_surface->h; y++) { for (int x = 0; x < reader->m_surface->w; x += 3) { int index = (y * reader->m_surface->w) + x; RGBColour colour = reader->getColourAt(x, y); newTexture[index] = colour.r; newTexture[index + 1] = colour.g; newTexture[index + 2] = colour.b; } } unsigned int id = m_renderer->createTextureFromData(newTexture, reader->m_surface->w, reader->m_surface->h, RGB); // functions for reading pixels RGBColour SDLSurfaceReader::getColourAt(int x, int y) { Uint32 pixel; Uint8 red, green, blue; RGBColour rgb; pixel = getPixel(m_surface, x, y); SDL_LockSurface(m_surface); SDL_GetRGB(pixel, m_surface->format, &red, &green, &blue); SDL_UnlockSurface(m_surface); rgb.r = red; rgb.b = blue; rgb.g = green; return rgb; } // this function taken from SDL documentation // http://www.libsdl.org/cgi/docwiki.cgi/Introduction_to_SDL_Video#getpixel Uint32 SDLSurfaceReader::getPixel(SDL_Surface* surface, int x, int y) { int bpp = m_surface->format->BytesPerPixel; Uint8 *p = (Uint8*)m_surface->pixels + y * m_surface->pitch + x * bpp; switch (bpp) { case 1: return *p; case 2: return *(Uint16*)p; case 3: if (SDL_BYTEORDER == SDL_BIG_ENDIAN) return p[0] << 16 | p[1] << 8 | p[2]; else return p[0] | p[1] << 8 | p[2] << 16; case 4: return *(Uint32*)p; default: return 0; } } I've been stumped at this, and I need help badly! Thanks so much for any advice.

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• Importing 3d model with multiple skeletons

  - by Sweta Dwivedi

  I have created an animated butterfly in 3ds Max and try to export it in ".fbx" format to use in XNA, however as soon as I compile, i get the following Errors: Warning 1 Multiple skeletons were found in the file. The first skeleton, named "Left.Wing" has been moved to be a child of the scene root. The other, "Right.Wing", will be ignored. Fragment identifier "Right.Wing". Error 2 Vertex is bound to bone "Right.Wing", but this bone is not present in the skeleton. Which is confusing since I have the bone Right.Wing . . and I use it to animate the butterfly I have seen a few possible solution for Blender but none for 3Ds max it would be really helpful if someone could help me out with this

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• Linking one uniform variable to many shaders

  - by Winged

  Let's say, that I have 3 programs, and in each of those programs there is a view matrix uniform, which should be the same in all those programs. Right now, when my camera moves, I need to re-upload the modified matrix to every program separately. Is it possible to create some kind of global uniforms which are constant for all programs linked to it, so I could just upload the matrix once? I tried creating a globalUniforms object which looked kinda like this: var globalUniforms = { program: {}, // (...) vMatrixUniform: null, // (...) initialize: function() { vMatrixUniform = gl.getUniformLocation(this.program, 'uVMatrix'); } }; So I could just link it to proper programs like this: program.vMatrixUniform = globalUniforms.vMatrixUniform;, and then pass the matrix like this: if (camera.isDirty.viewMatrix !== false) { camera.isDirty.viewMatrix = false; gl.uniformMatrix4fv(globalUniforms.vMatrixUniform, false, camera.viewMatrix.element); } but unfortunately it throws an error: Uncaught exception: gl.INVALID_VALUE was caused by call to: getUniformLocation called from line 272, column 2 in () in mysite/js/mesh.js: vMatrixUniform = gl.getUniformLocation(this.program, 'uVMatrix'); Summing up: is there a more efficient way of managing shaders which follows my logic?

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