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• Can't use the hardware scissor any more, should I use the stencil buffer or manually clip sprites?

  - by Alex Ames

  I wrote a simple UI system for my game. There is a clip flag on my widgets that you can use to tell a widget to clip any children that try to draw outside their parent's box (for scrollboxes for example). The clip flag uses glScissor, which is fed an axis aligned rectangle. I just added arbitrary rotation and transformations to my widgets, so I can rotate or scale them however I want. Unfortunately, this breaks the scissor that I was using as now my clip rectangle might not be axis aligned. There are two ways I can think of to fix this: either by using the stencil buffer to define the drawable area, or by having a wrapper function around my sprite drawing function that will adjust the vertices and texture coords of the sprites being drawn based on the clipper on the top of a clipper stack. Of course, there may also be other options I can't think of (something fancy with shaders possibly?). I'm not sure which way to go at the moment. Changing the implementation of my scissor functions to use the stencil buffer probably requires the smallest change, but I'm not sure how much overhead that has compared to the coordinate adjusting or if the performance difference is even worth considering.

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• changing body type without change of center of mass

  - by philipp

  I have an box2d project with some bodies in it, which move around without any user interaction. But if the user selects one of the bodies, he should be able to move it around just like he wants to. To keep it short, I want to change the type of the body to "kinematic" while the user controls it and back to "dynamic" afterwards. If I do so the rotation center of the body changes with the change of the type. How can I reset this? The body's fixture is created of a single b2PolygonShape, with its vertices set via SetAsArray(). Greetings philipp EDIT:: So I looked around about setting the local center of bodies. what brought me to this solution: var md = new b2MassData(); this.body.GetMassData( md ); this.body.SetType( b2body.b2_kinematicBody ); this.body.SetMassData( md ); that did not work, so I had a look at the source and found that SetMassData() always returns if the body is not "dynamic". So I tried this: var md = new b2MassData(); this._body.GetMassData( md ); this._body.SetType( b2Body.b2_kinematicBody ); this._body.m_sweep.localCenter.Set( md.center.x, md.center.y ); what actually is modifying the private data of the body. But it works and no errors appear, but can I really do this without the risk of breaking the application, or in other words, under which circumstances could this solution might cause errors? n.b.: I am using box2dweb of the latest release. Greetings philipp

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• Strange mesh import problem with Assimp and OpenGL

  - by Morgan

  Using the assimp library for importing 3D data into an OpenGL application. I get some strange problems regarding indexing of the vertices: If I use the following code for importing vertex indices: for (unsigned int t = 0; t < mesh->mNumFaces; ++t) { const struct aiFace * face = &mesh->mFaces[t]; if (face->mNumIndices == 3) { indices->push_back(face->mIndices[0]); indices->push_back(face->mIndices[1]); indices->push_back(face->mIndices[2]); } } I get the following result: Instead, if I use the following code: for(int k = 0; k < 2 ; k++) { for (unsigned int t = 0; t < mesh->mNumFaces; ++t) { const struct aiFace * face = &mesh->mFaces[t]; if (face->mNumIndices == 3) { indices->push_back(face->mIndices[0]); indices->push_back(face->mIndices[1]); indices->push_back(face->mIndices[2]); } } } I get the correct result: Hence adding the indices twice, renders the correct result? The OpenGL buffer is populated, like so: glBufferData(GL_ELEMENT_ARRAY_BUFFER, indices->size() * sizeof(unsigned int), indices->data(), GL_STATIC_DRAW); And rendered as follows: glDrawElements(GL_TRIANGLES, vertexCount*3, GL_UNSIGNED_INT, indices->data());

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• Partial recalculation of visibility on a 2D uniform grid

  - by Martin Källman

  Problem Imagine that we have a 2D uniform grid of dimensions N x N. For this grid we have also pre-computed a visibility look-up table, e.g. with DDA, which answers the boolean query is cell X visible from cell Y? The look-up table is a complete graph KN of the cells V in the grid, with each edge E being a binary value denoting the visibility between its vertices. Question If any given cell has its visibility modified, is it possible to extract the subset Edelta of edges which must have their visibility recomputed due to the change, so as to avoid a full-on recomputation for the entire grid? (Which is N(N-1) / 2 or N2 depending on the implementation) Update If is not possible to solve thi in closed form, then maintaining a separate mapping of each cell and every cell pair who's line intersects said cell might also be an option. This obviously consumes more memory, but the data is static. The increased memory requirement could be reduced by introducing a hierarchy, subdividing the grid into smaller parts, and by doing so the above mapping can be reused for each sub-grid. This would come at a cost in terms of increased computation relative to the number of subdivisions; also requiring a resumable ray-casting algorithm.

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• OpenGL CPU vs. GPU

  - by Nitrex88

  So I've always been under the impression that doing work on the GPU is always faster than on the CPU. Because of this, in OpenGL, I usually try to do intensive tasks in shaders so they get the speed boost from the GPU. However, now I'm starting to realize that some things simply work better on the CPU and actually perform worse on the GPU (particularly when a geometry shader is involved). For example, in a recent project I did involving procedurally generated terrain, I tried passing a grid of single triangles into a geometry shader, and tesselated each of these triangles into quads with 400 vertices whose height was determined by a noise function. This worked fine, and looked great, but easily maxed out the GPU with only 25 base triangles and caused a very slow framerate. I then discovered that tesselating on the CPU instead, and setting the height (using noise function) in the vertex shader was actually faster! This prompted me to question the benefits of using the GPU as much as possible... So, I was wondering if someone could describe the general pros and cons of using the GPU vs CPU for intensive graphics tasks. I know this mainly comes down to what your trying to achieve, so if necessary, use the above scenario to discuss why the "CPU + vertex shader" was actually faster than doing everything in the geometry shader on the GPU. It's possible my hardware (newest macbook pro) isn't optomized well for the geometry shader (thus causing the slow framerate). Also, I read that the vertex shader is very good with parallelism, and would love a quick explanation of how this may have played a role in speeding up my procedural terrain. Any info/advice about CPU/GPU/shaders would be awesome!

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• What are the maths behind 'Raiden 2' purple laser?

  - by Aybe

  The path of the laser is affected by user input and enemies present on the screen. Here is a video, at 5:00 minutes the laser in question is shown : Raiden II (PS) - 1 Loop Clear - Part 2 UPDATE Here is a test using Inkscape, ship is at bottom, the first 4 enemies are targeted by the plasma. There seems to be a sort of pattern. I moved the ship first, then the handle from it to form a 45° angle, then while trying to fit the curve I found a pattern of parallel handles and continued so until I reached the last enemy. Update, 5/26/2012 : I started an XNA project using beziers, there is still some work needed, will update the question next week. Stay tuned ! Update : 5/30/2012 : It really seems that they are using Bézier curves, I think I will be able to replicate/imitate a plasma of such grade. There are two new topics I discovered since last time : Arc length, Runge's phenomenon, first one should help in having a linear movement possible over a Bézier curve, second should help in optimizing the number of vertices. Next time I will put a video so you can see the progress 8-)

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• OpenGL CPU vs. GPU

  - by Nitrex88

  So I've always been under the impression that doing work on the GPU is always faster than on the CPU. Because of this, in OpenGL, I usually try to do intensive tasks in shaders so they get the speed boost from the GPU. However, now I'm starting to realize that some things simply work better on the CPU and actually perform worse on the GPU (particularly when a geometry shader is involved). For example, in a recent project I did involving procedurally generated terrain, I tried passing a grid of single triangles into a geometry shader, and tesselated each of these triangles into quads with 400 vertices whose height was determined by a noise function. This worked fine, and looked great, but easily maxed out the GPU with only 25 base triangles and caused a very slow framerate. I then discovered that tesselating on the CPU instead, and setting the height (using noise function) in the vertex shader was actually faster! This prompted me to question the benefits of using the GPU as much as possible... So, I was wondering if someone could describe the general pros and cons of using the GPU vs CPU for intensive graphics tasks. I know this mainly comes down to what your trying to achieve, so if necessary, use the above scenario to discuss why the "CPU + vertex shader" was actually faster than doing everything in the geometry shader on the GPU. It's possible my hardware (newest macbook pro) isn't optomized well for the geometry shader (thus causing the slow framerate). Also, I read that the vertex shader is very good with parallelism, and would love a quick explanation of how this may have played a role in speeding up my procedural terrain. Any info/advice about CPU/GPU/shaders would be awesome!

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• Seeking an C/C++ OBJ geometry read/write that does not modify the representation

  - by Blake Senftner

  I am seeking a means to read and write OBJ geometry files with logic that does not modify the geometry representation. i.e. read geometry, immediately write it, and a diff of the source OBJ and the one just written will be identical. Every OBJ writing utility I've been able to find online fails this test. I am writing small command line tools to modify my OBJ geometries, and I need to write my results, not just read the geometry for rendering purposes. Simply needing to write the geometry knocks out 95% of the OBJ libraries on the web. Also, many of the popular libraries modify the geometry representation. For example, Nat Robbin's GLUT library includes the GLM library, which both converts quads to triangles, as well as reverses the topology (face ordering) of the geometry. It's still the same geometry, but if your tool chain expects a given topology, such as for rigging or morph targets, then GLM is useless. I'm not rendering in these tools, so dependencies like OpenGL or GLUT make no sense. And god forbid, do not "optimize" the geometry! Redundant vertices are on purpose for maintaining oneself on cache with our weird little low memory mobile devices.

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• What to include in metadata?

  - by shyam

  I'm wondering if there are any general guidelines or best practices regarding when to split data into a metadata format, as oppose to directly embedding it within the data. (Specific example below). My understanding of metadata is that it describes data (without the need to actually look at the data), allowing for data to be quickly search/filtered for easy access. Let's take for example a simple 3D model format. The actual data file itself is a binary file containing vertices and colors. Things like creation date, modified data and author name would be things that describe the binary data, so I would say these belong as metadata (outside of the binary file). But what if the application had no need to search or filter by these fields? Would it be acceptable to embed these fields directly into the binary data itself? Could they be duplicated in both the binary data and the meta data, or would this be considered bad practice? What about more ambiguous fields such as the model name, which could be considered part of the data itself, but also as data describing the binary data?... How do you decide which data to embed in the actual binary file, as opposed to separating into a more flexible metadata format? Thanks!

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• OpenGL Tessellation makes point

  - by urza57

  A little problem with my tessellation shader. I try to implement a simple tessellation shader but it only makes points. Here's my vertex shader : out vec4 ecPosition; out vec3 ecNormal; void main( void ) { vec4 position = gl_Vertex; gl_Position = gl_ModelViewProjectionMatrix * position; ecPosition = gl_ModelViewMatrix * position; ecNormal = normalize(gl_NormalMatrix * gl_Normal); } My tessellation control shader : layout(vertices = 3) out; out vec4 ecPosition3[]; in vec3 ecNormal[]; in vec4 ecPosition[]; out vec3 myNormal[]; void main() { gl_out[gl_InvocationID].gl_Position = gl_in[gl_InvocationID].gl_Position; myNormal[gl_InvocationID] = ecNormal[gl_InvocationID]; ecPosition3[gl_InvocationID] = ecPosition[gl_InvocationID]; gl_TessLevelOuter[0] = float(4.0); gl_TessLevelOuter[1] = float(4.0); gl_TessLevelOuter[2] = float(4.0); gl_TessLevelInner[0] = float(4.0); } And my Tessellation Evaluation shader: layout(triangles, equal_spacing, ccw) in; in vec3 myNormal[]; in vec4 ecPosition3[]; out vec3 ecNormal; out vec4 ecPosition; void main() { float u = gl_TessCoord.x; float v = gl_TessCoord.y; float w = gl_TessCoord.z; vec3 position = vec4(gl_in[0].gl_Position.xyz * u + gl_in[1].gl_Position.xyz * v + gl_in[2].gl_Position.xyz * w ); vec3 position2 = vec4(ecPosition3[0].xyz * u + ecPosition3[1].xyz * v + ecPosition3[2].xyz * w ); vec3 normal = myNormal[0] * u + myNormal[1] * v + myNormal[2] * w ); ecNormal = normal; gl_Position = vec4(position, 1.0); ecPosition = vec4(position2, 1.0); } Thank you !

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• How do I use depth testing and texture transparency together in my 2.5D world?

  - by nbolton

  Note: I've already found an answer (which I will post after this question) - I was just wondering if I was doing it right, or if there is a better way. I'm making a "2.5D" isometric game using OpenGL ES (JOGL). By "2.5D", I mean that the world is 3D, but it is rendered using 2D isometric tiles. The original problem I had to solve was that my textures had to be rendered in order (from back to front), so that the tiles overlapped properly to create the proper effect. After some reading, I quickly realised that this is the "old hat" 2D approach. This became difficult to do efficiently, since the 3D world can be modified by the player (so stuff can appear anywhere in 3D space) - so it seemed logical that I take advantage of the depth buffer. This meant that I didn't have to worry about rendering stuff in the correct order. However, I faced a problem. If you use GL_DEPTH_TEST and GL_BLEND together, it creates an effect where objects are blended with the background before they are "sorted" by z order (meaning that you get a weird kind of overlap where the transparency should be). Here's some pseudo code that should illustrate the problem (incidentally, I'm using libgdx for Android). create() { // ... // some other code here // ... Gdx.gl.glEnable(GL10.GL_DEPTH_TEST); Gdx.gl.glEnable(GL10.GL_BLEND); } render() { Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT); Gdx.gl.glBlendFunc(GL10.GL_SRC_ALPHA, GL10.GL_ONE_MINUS_SRC_ALPHA); // ... // bind texture and create vertices // ... } So the question is: How do I solve the transparency overlap problem?

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• Illumination and Shading for computer graphics class

  - by Sam I Am

  I am preparing for my test tomorrow and this is one of the practice questions. I solved it partially but I am confused with the rest. Here is the problem: Consider a gray world with no ambient and specular lighting ( only diffuse lighting). The screen coordinates of a triangle P1,P2,P3, are P1=(100,100), P2= (300,150), P3 = (200, 200). The gray values at P!,P2,P3 are 1/2, 3/4, and 1/4 respectively. The light is at infinity and its direction and gray color are (1,1,1) and 1.0 respectively. The coefficients of diffused reflection is 1/2. The normals of P1,P2,P3 are N1= (0,0,1), N2 = (1,0,0), and N3 = (0,1,0) respectively. Consider the coordinates of three points P1,P2,P3 to be 0. Do not normalize the normals. I have computed that the illumination at the 3 vertices P1,P2,P3 is (1/4,3/8,1/8). Also I computed that interpolation coefficients of a point P inside the triangle whose coordinates are (220, 160) are given by (1/5,2/5,2/5). Now I have 4 more questions regarding this problem. 1) The illumination at P using Gouraud Shading is: i) 1/2 The answer is 1/2, but I have no idea how to compute it.. 2) The interpolated normal at P is given by i) (2/5, 2/5,1/5) ii) (1/2, 1/4, 1/4) iii) (3/5, 1/5, 1/5) 3) The interpolated color at P is given by: i) 1/2 Again, I know the correct answer but no idea how to solve it 4) The illumination at P using Phong Shading is i) 1/4 ii) 9/40 iii) 1/2

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• geomipmapping using displacement mapping (and glVertexAttribDivisor)

  - by Will

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

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• Sending changes to a terrain heightmap over UDP

  - by Floomi

  This is a more conceptual, thinking-out-loud question than a technical one. I have a 3D heightmapped terrain as part of a multiplayer RTS that I would like to terraform over a network. The terraforming will be done by units within the gameworld; the player will paint a "target heightmap" that they'd like the current terrain to resemble and units will deform towards that on their own (a la Perimeter). Given my terrain is 257x257 vertices, the naive approach of sending heights when they change will flood the bandwidth very quickly - updating a quarter of the terrain every second will hit ~66kB/s. This is clearly way too much. My next thought was to move to a brush-based system, where you send e.g. the centre of a circle, its radius, and some function defining the influence of the brush from the centre going outwards. But even with reliable UDP the "start" and "stop" messages could still be delayed. I guess I could compare timestamps and compensate for this, although it'd likely mean that clients would deform verts too much on their local simulations and then have to smooth them back to the correct heights. I could also send absolute vert heights in the "start" and "stop" messages to guarantee correct data on the clients. Alternatively I could treat brushes in a similar way to units, and do the standard position + velocity + client-side prediction jazz on them, with the added stipulation that they deform terrain within a certain radius around them. The server could then intermittently do a pass and send (a subset of) recently updated verts to clients as and when there's bandwidth to spare. Any other suggestions, or indications that I'm on the right (or wrong!) track with any of these ideas would be greatly appreciated.

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• What is UVIndex and how do I use it on OpenGL?

  - by Delta

  I am a noob in OpenGL ES 2.0 (for WebGL) and I'm trying to draw a simple model I've made with a 3D tool and exported to .fbx format. I've been able to draw some models that only have: A vertex buffer, a index buffer for the vertices, a normal buffer and a texture coordinate buffer, but this model now has a "UVIndex" and I'm not sure where am I supposed to put this UVIndex. My code looks like this: GL.bindBuffer(GL.ARRAY_BUFFER, this.Model.House.VertexBuffer); GL.vertexAttribPointer(this.Shader.TextureAndLighting.Attribute["vPosition"],3,GL.FLOAT, false, 0, 0); GL.bindBuffer(GL.ARRAY_BUFFER, this.Model.House.NormalBuffer); GL.vertexAttribPointer(this.Shader.TextureAndLighting.Attribute["vNormal"], 3, GL.FLOAT, false, 0, 0); GL.bindBuffer(GL.ARRAY_BUFFER, this.Model.House.TexCoordBuffer); GL.vertexAttribPointer(this.Shader.TextureAndLighting.Attribute["TexCoord"], 2, GL.FLOAT, false, 0, 0); GL.bindBuffer(GL.ELEMENT_ARRAY_BUFFER, this.Model.House.IndexBuffer); GL.bindTexture(GL.TEXTURE_2D, this.Texture.HTex1); GL.activeTexture(GL.TEXTURE0); GL.drawElements(GL.TRIANGLES, this.Model.House.IndexBuffer.Length, GL.UNSIGNED_SHORT, 0); But my model renders totally incorrect and I think it has to do with the fact that I am ignoring this "UVIndex" in the .fbx file, since I've never drawn any model that uses this UVIndex I really have no clue on what to do with it. This is the json file containing the model's data: http://pastebin.com/raw.php?i=G294TVmz

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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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• cocos2d/OpenGL multitexturing problem

  - by Gajoo

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

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• Directional and orientation problem

  - by Ahmed Saleh

  I have drawn 5 tentacles which are shown in red. I have drew those tentacles on a 2D Circle, and positioned them on 5 vertices of the that circle. BTW, The circle is never be drawn, I have used it to simplify the problem. Now I wanted to attached that circle with tentacles underneath the jellyfish. There is a problem with the current code but I don't know what is it. You can see that the circle is parallel to the base of the jelly fish. I want it to be shifted so that it be inside the jelly fish. but I don't know how. I tried to multiply the direction vector to extend it but that didn't work. // One tentacle is constructed from nodes // Get the direction of the first tentacle's node 0 to node 39 of that tentacle; Vec3f dir = m_tentacle[0]->geNodesPos()[0] - m_tentacle[0]->geNodesPos()[39]; // Draw the circle with tentacles on it Vec3f pos = m_SpherePos; drawCircle(pos,dir,30,m_tentacle.size()); for (int i=0; i<m_tentacle.size(); i++) { m_tentacle[i]->Draw(); } // Draw the jelly fish, and orient it on the 2D Circle gl::pushMatrices(); Quatf q; // assign quaternion to rotate the jelly fish around the tentacles q.set(Vec3f(0,-1,0),Vec3f(dir.x,dir.y,dir.z)); // tanslate it to the position of the whole creature per every frame gl::translate(m_SpherePos.x,m_SpherePos.y,m_SpherePos.z); gl::rotate(q); // draw the jelly fish at center 0,0,0 drawHemiSphere(Vec3f(0,0,0),m_iRadius,90); gl::popMatrices();

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• Matrix.CreateBillboard centre rotation problem

  - by Chris88

  I'm having an issue with Matrix.CreateBillboard and a textured Quad where the center axis seems to be positioned incorrectly to the quad object which is rotating around a center point: Using: BasicEffect quadEffect; Drawing the quad shape: Left = Vector3.Cross(Normal, Up); Vector3 uppercenter = (Up * height / 2) + origin; LowerLeft = uppercenter + (Left * width / 2); LowerRight = uppercenter - (Left * width / 2); UpperLeft = LowerLeft - (Up * height); UpperRight = LowerRight - (Up * height); Where height and width are float values passed in (it draws a square) Draw method: quadEffect.View = camera.view; quadEffect.Projection = camera.projection; quadEffect.World = Matrix.CreateBillboard(Origin, camera.cameraPosition, Vector3.Up, camera.cameraDirection); GraphicsDevice.BlendState = BlendState.Additive; foreach (EffectPass pass in quadEffect.CurrentTechnique.Passes) { pass.Apply(); GraphicsDevice.DrawUserIndexedPrimitives <VertexPositionNormalTexture>( PrimitiveType.TriangleList, Vertices, 0, 4, Indexes, 0, 2); } GraphicsDevice.BlendState = BlendState.Opaque; In the screenshots below i draw the image at Vector3(32f, 0f, 32f) The screenshots below show you the position of the quad in relation to the red cross. The red cross shows where it should be drawn http://i.imgur.com/YwRYj.jpg http://i.imgur.com/ZtoHL.jpg It rotates around the red cross position

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• backface culling error (in world space)

  - by acrilige

  I write simple software renderer. In my pipeline i have stage of backface culling. But looks like it has some error (see picture). I perform culling right after world transformation (is it correct?). (i can't insert picture in post coz i don't have enough points, so i just upload it (cube model): http://imageshack.us/photo/my-images/705/bcerror.png/) Vector3F view_dir(0.0f, 0.0f, 1.0f); std::vector<Triangle> to_remove; for (Triangle &t : m_triangles) { Vector4F e1 = t.v2 - t.v1; Vector4F e2 = t.v3 - t.v1; Vector3F normal( e1.y * e2.z - e1.z * e2.y, e1.z * e2.x - e1.x * e2.z, e1.x * e2.y - e1.y * e2.x ); normal.Normalize(); float dot = Dot(view_dir, normal); if (dot <= 0) to_remove.push_back(t); } for (Triangle& t : to_remove) m_triangles.erase(std::remove(m_triangles.begin(), m_triangles.end(), t), m_triangles.end()); Camera sits in origin and points in screen (RH). What is the reason? For better explanation i upload picture with cube rotation screenshots: http://imageshack.us/photo/my-images/842/bcmove.png/ UPDATED: The error occurs only when triangle has non-zero offset from origin UPDATED 2: If i process backface culling in clip space (after transforming all vertices with view and projection matrix), and just check z coordinate of triangle normal - it works perfect... Can i perform culing RIGHT BEFORE view/proj transforms? In this case looks like culling will not depends of projection and it's not right?.. UPDATED 3: I found answer and will post it in two hours - again coz of reputation lack.

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• High resolution graphical representation of the Earth's surface

  - by Simon

  I've got a library, which I inherited, which presents a zoomable representation of the Earth. It's a Mercator projection and is constructed from triangles, the properties of which are stored in binary files. The surface is built up, for any given view port, by drawing these triangles in an overlapping fashion to produce the image. The definition of each triangle is the lat/long of the vertices. It looks OK at low values of zoom but looks progressively more ragged as the user zooms in. The view ports are primarily referenced though a rectangle of lat/long co-ordinates. I'd like to replace it with a better quality approach. The problem is, I don't know where to begin researching the options as I am not familiar either with the projections needed nor the graphics techniques used to render them. For example, I imagine that I could acquire high resolution images, say Mercator projections although I'm open to anything, break them into tiles and somehow wrap them onto a graphical representation of a sphere. I'm not asking for "how do I", more where should I begin to understand what might be involved and the techniques I will need to learn. I am most grateful for any "Earth rendering 101" pointers folks might have.

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• OpenGL lighting with dynamic geometry

  - by Tank

  I'm currently thinking hard about how to implement lighting in my game. The geometry is quite dynamic (fixed 3D grid with custom geometry in each cell) and needs some light to get more depth and in general look nicer. A scene in my game always contains sunlight and local light sources like lamps (point lights). One can move underground, so sunlight must be able to illuminate as far as it can get. Here's a render of a typical situation: The lamp is positioned behind the wall to the top, and in the hollow cube there's a hole in the back, so that light can shine through. (I don't want soft shadows, this is just for illustration) While spending the whole day searching through Google, I stumbled on some keywords like deferred rendering, forward rendering, ambient occlusion, screen space ambient occlusion etc. Some articles/tutorials even refer to "normal shading", but to be honest I don't really have an idea to even do simple shading. OpenGL of course has a fixed lighting pipeline with 8 possible light sources. However they just illuminate all vertices without checking for occluding geometry. I'd be very thankful if someone could give me some pointers into the right direction. I don't need complete solutions or similar, just good sources with information understandable for someone with nearly no lighting experience (preferably with OpenGL).

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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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• Using a Vertex Buffer and DrawUserIndexedPrimitives?

  - by MattMcg

  Let's say I have a large but static world and only a single moving object on said world. To increase performance I wish to use a vertex and index buffer for the static part of the world. I set them up and they work fine however if I throw in another draw call to DrawUserIndexedPrimitives (to draw my one single moving object) after the call to DrawIndexedPrimitives, it will error out saying a valid vertex buffer must be set. I can only assume the DrawUserIndexedPrimitive call destroyed/replaced the vertex buffer I set. In order to get around this I must call device.SetVertexBuffer(vertexBuffer) every frame. Something tells me that isn't correct as that kind of defeats the point of a buffer? To shed some light, the large vertex buffer is the final merged mesh of many repeated cubes (think Minecraft) which I manually create to reduce the amount of vertices/indexes needed (for example two connected cubes become one cuboid, the connecting faces are cut out), and also the amount of matrix translations (as it would suck to do one per cube). The moving objects would be other items in the world which are dynamic and not fixed to the block grid, so things like the NPCs who move constantly. How do I go about handling the large static world but also allowing objects to freely move about?

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• Colored Collision Detection

  - by tugrul büyükisik

  Several years ago, i made a fast collision detection for 2D, it was just checking a bullets front-pixel's color to check if it were to hit something. Lets say the target rgb color is (124,200,255) then it just checks for that color. After the collision detection, it paints the target with appropriate picture. So, collision detection is made in background without drawing but then painted and drawed. How can i do this in 3D? Because, a vertex is not just exist like a 2D picture's pixel. I looked at some java3D and other programs and understood that 3D world is made of objects. Not just pictures. Is there a program that truly fills the world with vertices ? But it could be needing terabytes of ram even more. Do you know an easy way to interpolate the color of a vertex in java3D or similar program? Note: for a rgb color-identifier, i can make 255*255*255 different 2D objects in background.

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