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  • A two way minimum spanning tree of a directed graph

    - by mvid
    Given a directed graph with weighted edges, what algorithm can be used to give a sub-graph that has minimum weight, but allows movement from any vertex to any other vertex in the graph (under the assumption that paths between any two vertices always exist). Does such an algorithm exist?

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  • How do I define and standardize units in my 3D app?

    - by Omega
    I'm starting to design my object graph for an OpenGL ES 1.1 on Android. What's advisable when it comes to actually drawing my triangles when it comes to controlling their size? Should I store all the vertices in units relative to each other and then multiply them by a value I pass during a draw(GL10 gl)? Would this approach have any impact when it comes time to do frustum culling?

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  • Debugging a basic OpenGL texture fail? (iphone)

    - by Ben
    Hey all, I have a very basic texture map problem in GL on iPhone, and I'm wondering what strategies there are for debugging this kind of thing. (Frankly, just staring at state machine calls and wondering if any of them is wrong or misordered is no way to live-- are there tools for this?) I have a 512x512 PNG file that I'm loading up from disk (not specially packed), creating a CGBitmapContext, then calling CGContextDrawImage to get bytes out of it. (This code is essentially stolen from an Apple sample.) I'm trying to map the texture to a "quad", with code that looks essentially like this-- all flat 2D stuff, nothing fancy: glEnable(GL_TEXTURE_2D); glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); glEnableClientState(GL_TEXTURE_COORD_ARRAY); GLfloat vertices[8] = { viewRect.origin.x, viewRect.size.height, viewRect.origin.x, viewRect.origin.y, viewRect.size.width, viewRect.origin.y, viewRect.size.width, viewRect.size.height }; GLfloat texCoords[8] = { 0, 1.0, 0, 0, 1.0, 0, 1.0, 1.0 }; glBindTexture(GL_TEXTURE_2D, myTextureRef); // This was previously bound to glVertexPointer(2, GL_FLOAT , 0, vertices); glTexCoordPointer(2, GL_FLOAT, 0, texCoords); glDrawArrays(GL_TRIANGLE_FAN, 0, 4); glDisableClientState(GL_TEXTURE_COORD_ARRAY); glDisable(GL_TEXTURE_2D); My supposedly textured area comes out just black. I see no debug output from the CG calls to set up the texture. glGetError reports nothing. If I simplify this code block to just draw the verts, but set up a pure color, the quad area lights up exactly as expected. If I clear the whole context immediately beforehand to red, I don't see the red-- which means something is being rendered there, but not the contents of my PNG. What could I be doing wrong? And more importantly, what are the right tools and techniques for debugging this sort of thing, because running into this kind of problem and not being able to "step through it" in a debugger in any meaningful way is a bummer. Thanks!

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  • Boost BGL thread safety

    - by Budzoli
    Hi! I'd like multiple threads to use the dijkstra_shortest_paths and astar_search functions of the BGL, and then read the property maps of the result vertices and edges. I'm wondering wether I should use mutexes to ensure thread-safety. So here are my questions: 1., Are the dijkstra_shortest_paths and astar_search functions of the Boost.Graph thread safe? 2., If I only try to read the property maps of the graph from multiple threads, do I need to worry about thread safety?

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  • What is the best way to debug OpenGL?

    - by dreamlax
    I find that a lot of the time, OpenGL will show you it failed by not drawing anything. I'm trying to find ways to debug OpenGL programs, by inspecting the transformation matrix stack and so on. What is the best way to debug OpenGL? If the code looks and feels like the vertices are in the right place, how can you be sure they are?

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  • Making a grid on iPhone using Opengl

    - by TheGambler
    I'm trying to make a grid similar to what you would see in these geo games(geoDefense/geometry wars). I'm wanting to apply separate transformation matrixes to each to create different effects. So, it makes since to me that I need to draw each square separately to that I can apply a different transformation to each one. The problem I'm having is mapping these grids out or connecting the squares. The coordinate systems is still confusing to me. I know it would be easy just to create a huge triangle strip but I'm not able to figure out a way to apply separate transformations to each square( quad ) if I use triangle strips. So first question: Can you apply different transformations to quads if you use a triangle strip to draw a huge grid? If so, any tips suggestions on how to do so? If not, how does one usually connect textures without using triangle strips? Here is my coord setup: const GLfloat zNear = 0.01, zFar = 1000.0, fieldOfView = 45.0; GLfloat size; glEnable(GL_DEPTH_TEST); glMatrixMode(GL_PROJECTION); size = zNear * tanf(DEGREES_TO_RADIANS(fieldOfView) / 2.0); CGRect rect = view.bounds; glFrustumf(-size, size, -size / (rect.size.width / rect.size.height), size / (rect.size.width / rect.size.height), zNear, zFar); glViewport(0, 0, rect.size.width, rect.size.height); Here is my draw: - (void)drawView:(GLView*)view; { int loop; //glColor4f(1.0, 1.0, 1.0, 0.5); glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); //Grid Loop for( loop = 0; loop < kNumberSectionsInGrid; loop++ ) { //glLoadIdentity(); static Matrix3D shearMatrix; Matrix3DSetShear(shearMatrix, 0.2, 0.2); static Matrix3D finalMatrix; //Matrix3DMultiply(temp2Matrix, shearMatrix, finalMatrix); glLoadMatrixf(shearMatrix); glTranslatef(-1.0f,(float)loop,-3.0f); glScalef(0.1, 0.1, 0.0); Vertex3D vertices[] = { {-1.0, 1.0, 0.5}, { 1.0, 1.0, 0.5}, { -1.0, -1.0, 0.5}, { 1.0, -1.0, 0.5} }; static const Vector3D normals[] = { {0.0, 0.0, 1.0}, {0.0, 0.0, 1.0}, {0.0, 0.0, 1.0}, {0.0, 0.0, 1.0}, }; GLfloat texCoords[] = { 0.0, 1.0, 1.0, 1.0, 0.0, 0.0, 1.0, 0.0 }; glEnableClientState(GL_VERTEX_ARRAY); glEnableClientState(GL_NORMAL_ARRAY); glEnableClientState(GL_TEXTURE_COORD_ARRAY); glBindTexture(GL_TEXTURE_2D, texture[0]); glVertexPointer(3, GL_FLOAT, 0, vertices); glNormalPointer(GL_FLOAT, 0, normals); glTexCoordPointer(2, GL_FLOAT, 0, texCoords); glDrawArrays(GL_TRIANGLE_STRIP, 0, 4); glDisableClientState(GL_VERTEX_ARRAY); glDisableClientState(GL_NORMAL_ARRAY); glDisableClientState(GL_TEXTURE_COORD_ARRAY); } } glMatrixMode(GL_MODELVIEW);

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  • Concatenation of many lists in Python

    - by Space_C0wb0y
    Suppose i have a function like this: def getNeighbors(vertex) which returns a list of vertices that are neighbors of the given vertex. Now i want to create a list with all the neighbors of the neighbors. I do that like this: listOfNeighborsNeighbors = [] for neighborVertex in getNeighbors(vertex): listOfNeighborsNeighbors.append(getNeighbors(neighborsVertex)) Is there a more pythonic way to do that?

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  • XNA 4.0 draw a cube with DrawUserIndexedPrimitives method [on hold]

    - by Leggy7
    EDIT Since I read what Mark H suggested (thanks a lot, I found it very useful) I think my question can become clearer structured this way: Using XNA 4.0, I'm trying to draw a cube. Im using this method: GraphicsDevice.DrawUserIndexedPrimitives<VertexPositionColor>( PrimitiveType.LineList, primitiveList, 0, // vertex buffer offset to add to each element of the index buffer 8, // number of vertices in pointList lineListIndices, // the index buffer 0, // first index element to read 7 // number of primitives to draw ); I got the code sample from this page which simply draw a serie of triangles. I want to modify this code in order to draw a cube. I was able to slitghly move the camera so I can have the perception of solidity, I set the vertex array to contain the 8 points defining a cube. But I can't fully understand how many primitives I have to draw (last parameter) for each of PrimitiveType. So, I wasn't able to draw the cube (just some of the edges in a non-defined order). More in detail: to build the vertex index list, the sample used // Initialize an array of indices of type short. lineListIndices = new short[(points * 2) - 2]; // Populate the array with references to indices in the vertex buffer for (int i = 0; i < points - 1; i++) { lineListIndices[i * 2] = (short)(i); lineListIndices[(i * 2) + 1] = (short)(i + 1); } I'm ashamed to say I cannot do the same in the case of a cube. what has to be the size of the lineListIndices? how should I populate it? In which order? And how do these things change when I use a different PrimitiveType? In the code sample there are also another couple of calls which I cannot fully understand, which are: // Initialize the vertex buffer, allocating memory for each vertex. vertexBuffer = new VertexBuffer(graphics.GraphicsDevice, vertexDeclaration, points, BufferUsage.None); // Set the vertex buffer data to the array of vertices. vertexBuffer.SetData<VertexPositionColor>(pointList); and vertexDeclaration = new VertexDeclaration(new VertexElement[] { new VertexElement(0, VertexElementFormat.Vector3, VertexElementUsage.Position, 0), new VertexElement(12, VertexElementFormat.Color, VertexElementUsage.Color, 0) } ); that is, for VertexBuffer and VertexDeclaration I could not find and significant (monkey-like) guide. I reported them too because I think they could be involded in understanding things. I think I also have to understand something related to the order the vertexes are stored in the array. But actually I have no clue of what I should learn to have this function drawing a cube. So, if anybody could point me to the right direction, it wil be appreciated. Hope to have made myself clear this time

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  • RTS style fog of war woes

    - by Fricken Hamster
    So I'm trying to make a rts style line of sight fog of war style engine for my grid based game. Currently I am getting a set of vertices by raycasting in 360 degree. Then I use that list of vertices to do a graphics style polygon scanline fill to get a list of all points within the polygon. The I compare the new list of seen tiles and compare that with the old one and increment or decrement the world vision array as needed. The polygon scanline function is giving me trouble. I'm mostly following this http://www.cs.uic.edu/~jbell/CourseNotes/ComputerGraphics/PolygonFilling.html So far this is my code without cleaning anything up var edgeMinX:Vector.<int> = new Vector.<int>; var edgeMinY:Vector.<int> = new Vector.<int>; var edgeMaxY:Vector.<int> = new Vector.<int>; var edgeInvSlope:Vector.<Number> = new Vector.<Number>; var ilen:int = outvert.length; var miny:int = -1; var maxy:int = -1; for (i = 0; i < ilen; i++) { var curpoint:Point = outvert[i]; if (i == ilen -1) { var nextpoint:Point = outvert[0]; } else { nextpoint = outvert[i + 1]; } if (nextpoint.y == curpoint.y) { continue; } if (curpoint.y < nextpoint.y) { var curslope:Number = ((nextpoint.y - curpoint.y) / (nextpoint.x - curpoint.x)); edgeMinY.push(curpoint.y); edgeMinX.push(curpoint.x); edgeMaxY.push(nextpoint.y); edgeInvSlope.push(1 / curslope); if (curpoint.y < miny || miny == -1) { miny = curpoint.y; } if (nextpoint.y > maxy) { maxy = nextpoint.y; } } else { curslope = ((curpoint.y - nextpoint.y) / (curpoint.x - nextpoint.x)); edgeMinY.push(nextpoint.y); edgeMinX.push(nextpoint.x); edgeMaxY.push(curpoint.y); edgeInvSlope.push(1 / curslope); if (nextpoint.y < miny || miny == -1) { miny = curpoint.y; } if (curpoint.y > maxy) { maxy = nextpoint.y; } } } var activeMaxY:Vector.<int> = new Vector.<int>; var activeCurX:Vector.<Number> = new Vector.<Number>; var activeInvSlope:Vector.<Number> = new Vector.<Number>; for (var scanline:int = miny; scanline < maxy + 1; scanline++) { ilen = edgeMinY.length; for (i = 0; i < ilen; i++) { if (edgeMinY[i] == scanline) { activeMaxY.push(edgeMaxY[i]); activeCurX.push(edgeMinX[i]); activeInvSlope.push(edgeInvSlope[i]); //trace("added(" + edgeMinX[i]); edgeMaxY.splice(i, 1); edgeMinX.splice(i, 1); edgeMinY.splice(i, 1); edgeInvSlope.splice(i, 1); i--; ilen--; } } ilen = activeCurX.length; for (i = 0; i < ilen - 1; i++) { for (var j:int = i; j < ilen - 1; j++) { if (activeCurX[j] > activeCurX[j + 1]) { var tempint:int = activeMaxY[j]; activeMaxY[j] = activeMaxY[j + 1]; activeMaxY[j + 1] = tempint; var tempnum:Number = activeCurX[j]; activeCurX[j] = activeCurX[j + 1]; activeCurX[j + 1] = tempnum; tempnum = activeInvSlope[j]; activeInvSlope[j] = activeInvSlope[j + 1]; activeInvSlope[j + 1] = tempnum; } } } var prevx:int = -1; var jlen:int = activeCurX.length; for (j = 0; j < jlen; j++) { if (prevx == -1) { prevx = activeCurX[j]; } else { for (var k:int = prevx; k < activeCurX[j]; k++) { graphics.lineStyle(2, 0x124132); graphics.drawCircle(k * 20 + 10, scanline * 20 + 10, 5); if (k == prevx || k > activeCurX[j] - 1) { graphics.lineStyle(3, 0x004132); graphics.drawCircle(k * 20 + 10, scanline * 20 + 10, 2); } prevx = -1; //tileLightList.push(k, scanline); } } } ilen = activeCurX.length; for (i = 0; i < ilen; i++) { if (activeMaxY[i] == scanline + 1) { activeCurX.splice(i, 1); activeMaxY.splice(i, 1); activeInvSlope.splice(i, 1); i--; ilen--; } else { activeCurX[i] += activeInvSlope[i]; } } } It works in some cases but some of the x intersections are skipped, primarily when there are more than 2 x intersections in one scanline I think. Is there a way to fix this, or a better way to do what I described? Thanks

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  • Box 2d basic questions

    - by philipp
    I am a bit new to box2d and I am developing an game with type and letters. I am using an svg font and generate the box2d bodies direct from the glyphs path definition, using the convex hull of them. I also have an decomposition routine the decomposes this hull if necessary. All this it is more or less working, except that I got some strange errors which definitely are caused by the scale factors. The problem is caused by two factors: first: the world scale of box2d, second: the the precision of curve-approximation of the glyph vectors. So through scaling down the input vertices for box2d, it happens that they become equal caused by numerical precision, what causes errors in box2d. Through scaling the my glyphs a bit up, this goes away. I also goes away if I chose a different world scale factor, but this slows down the whole animation quite much! So if my view port is about 990px * 600px and i want to animate Glyphs in box2d which should have a size from about 50px * 50px up to 300px * 300px, which scale factor of the b2world should i choose? How small should the smallest distance from on vertex to another be, while approximating the glyph vectors? Thanks for help greetings philipp EDIT:: I continued reading the docs of box2d and after rethinking of the units system, which is designed to handle object from 0.1 up to 10 meters, I calculated a scale factor of 75. So Objects 600px width will are 8 meters wide in box2d and even small objects of about 20px width will become 0.26 meters width in box2d. I will go on trying with this values, but if there is somebody out there who could give me a clever advice i would be happy!

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  • Inter Quake Model IQM render Directx9

    - by Andrew_0
    I'm trying to render an Inter Quake Model(http://lee.fov120.com/iqm/) in DirectX9 that I exported from blender. I want to display animations which IQM supports and my model format does not. The model is a cylinder. It loads fine in the iqm sdk opengl viewer but when i try to render it in directx9 using for example(this is just to render the vertices): IDirect3DDevice9 * device; HRESULT hr = S_OK; for(int i = 0; i < nummeshes; i++) { iqmmesh &m = meshes[0]; hr = device->DrawIndexedPrimitiveUP(D3DPT_TRIANGLELIST, 0, 3*m.num_triangles, m.num_triangles ,&tris[m.first_triangle] ,D3DFMT_INDEX32 ,inposition ,sizeof(unsigned int)); } It renders like this: Incorrect The light grey bit that looks like two triangles in the middle is what is rendered(ignore the other stuff). Whereas it is meant to look like this(using a custom importer which I designed which matches what is displayed in blender): Correct Anyone have any suggestions on what might be going wrong?

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  • How can I reduce draw calls when using glBufferSubData and DYNAMIC_DRAW?

    - by Kronos
    At first I had the problem where I had about 150 rectangles rendered every tick. I only used STATIC_DRAW and glBufferData. I added support for DYNAMIC_DRAW and glBufferSubData and now I have a very good result... but the number of draw calls (glDrawArrays) is the same. Best practices from Mozilla Dev website said it should be reduced, but how? Every rectangle has a method render() in which I do following (shortend): _gl.bindBuffer(WebGL.ARRAY_BUFFER, vertexBuffer); _gl.enableVertexAttribArray(a_position); _gl.vertexAttribPointer(a_position, 2, WebGL.FLOAT, false, 0, 0); _gl.bufferSubData(WebGL.ARRAY_BUFFER, 0, vertices); _gl.bindBuffer(WebGL.ARRAY_BUFFER, texCoordBuffer); _gl.enableVertexAttribArray(a_texCoordLocation); _gl.vertexAttribPointer(a_texCoordLocation, 2, WebGL.FLOAT, false, 0, 0); _gl.bufferSubData(WebGL.ARRAY_BUFFER, 0, texVertices); _gl.uniform2fv(_utranslation, _translation); _gl.uniform2fv(_urotation, _rotation); _gl.uniform2f(_location, Dart2D.WIDTH, Dart2D.HEIGHT); _gl.drawArrays(WebGL.TRIANGLES, 0, 6); So every rectangle calls drawArrays in every frame...

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  • Depth interpolation for z-buffer, with scanline

    - by Twodordan
    I have to write my own software 3d rasterizer, and so far I am able to project my 3d model made of triangles into 2d space: I rotate, translate and project my points to get a 2d space representation of each triangle. Then, I take the 3 triangle points and I implement the scanline algorithm (using linear interpolation) to find all points[x][y] along the edges(left and right) of the triangles, so that I can scan the triangle horizontally, row by row, and fill it with pixels. This works. Except I have to also implement z-buffering. This means that knowing the rotated&translated z coordinates of the 3 vertices of the triangle, I must interpolate the z coordinate for all other points I find with my scanline algorithm. The concept seems clear enough, I first find Za and Zb with these calculations: var Z_Slope = (bottom_point_z - top_point_z) / (bottom_point_y - top_point_y); var Za = top_point_z + ((current_point_y - top_point_y) * Z_Slope); Then for each Zp I do the same interpolation horizontally: var Z_Slope = (right_z - left_z) / (right_x - left_x); var Zp = left_z + ((current_point_x - left_x) * Z_Slope); And of course I add to the zBuffer, if current z is closer to the viewer than the previous value at that index. (my coordinate system is x: left - right; y: top - bottom; z: your face - computer screen;) The problem is, it goes haywire. The project is here and if you select the "Z-Buffered" radio button, you'll see the results... (note that the rest of the options before "Z-Buffered" use the Painter's algorithm to correctly order the triangles. I also use the painter's algorithm -only- to draw the wireframe in "Z-Buffered" mode for debugging purposes) PS: I've read here that you must turn the z's into their reciprocals (meaning z = 1/z) before you interpolate. I tried that, and it appears that there's no change. What am I missing? (could anyone clarify, precisely where you must turn z into 1/z and where to turn it back?)

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  • Bone creation in XNA Content Pipeline

    - by cod3monk3y
    I'm trying to manually create a ModelContent instance that includes custom Bone data in a custom ContentProcessor in the XNA Content Pipeline. I can't seem to create or assign manually created bone data due to either private constructors or read-only collections (at every turn). The code I have right now that creates a single triangle ModelContent that I'd like to create a bone for is: MeshContent mc = new MeshContent(); mc.Positions.Add(new Vector3(-10, 0, 0)); mc.Positions.Add(new Vector3(0, 10, 0)); mc.Positions.Add(new Vector3(10, 0, 0)); GeometryContent gc = new GeometryContent(); gc.Indices.AddRange(new int[] { 0, 1, 2 }); gc.Vertices.AddRange(new int[] { 0, 1, 2 }); mc.Geometry.Add(gc); // Create normals MeshHelper.CalculateNormals(mc, true); // finally, convert it to a model ModelContent model = context.Convert<MeshContent, ModelContent>(mc, "ModelProcessor"); The documentation on XNA is amazingly sparse. I've been referencing the class diagrams created by DigitalRune and Sean Hargreaves blog, but I haven't found anything on creating bone content. Once the ModelContent is created, it's not possible to add bones because the Bones collection is read-only. And it seems the only way to create the ModelContent instance is to call the standard ModelProcessor via ContentProcessorContext.Convert. So it's a bit of a catch-22. The BoneContent class has a constructor but no methods except those inherited from NodeContent... though now (true to form) maybe I've realized the solution by asking the question. Should I create a root NodeContent with two children: one MeshContent and one BoneContent as the root of my skeleton; then pass the root NodeContent to ContentProcessorContext.Convert? Off to try that now...

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  • Writing the correct value in the depth buffer when using ray-casting

    - by hidayat
    I am doing a ray-casting in a 3d texture until I hit a correct value. I am doing the ray-casting in a cube and the cube corners are already in world coordinates so I don't have to multiply the vertices with the modelviewmatrix to get the correct position. Vertex shader world_coordinate_ = gl_Vertex; Fragment shader vec3 direction = (world_coordinate_.xyz - cameraPosition_); direction = normalize(direction); for (float k = 0.0; k < steps; k += 1.0) { .... pos += direction*delta_step; float thisLum = texture3D(texture3_, pos).r; if(thisLum > surface_) ... } Everything works as expected, what I now want is to sample the correct value to the depth buffer. The value that is now written to the depth buffer is the cube coordinate. But I want the value of pos in the 3d texture to be written. So lets say the cube is placed 10 away from origin in -z and the size is 10*10*10. My solution that does not work correctly is this: pos *= 10; pos.z += 10; pos.z *= -1; vec4 depth_vec = gl_ProjectionMatrix * vec4(pos.xyz, 1.0); float depth = ((depth_vec.z / depth_vec.w) + 1.0) * 0.5; gl_FragDepth = depth;

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  • Decal implementation

    - by dreta
    I had issues finding information about decals, so maybe this question will help others. The implementation is for a forward renderer. Could somebody confirm if i got decal implementation right? You define a cube of any dimension that'll define the projection volume in common space. You check for triangle intersection with the defined cube to recieve triangles that the projection will affect. You clip these triangles and save them. You then use matrix tricks to calculate UV coordinates for the saved triangles that'll reference the texture you're projecting. To do this you take the vectors representing height, width and depth of the cube in common space, so that f.e. the bottom left corner is the origin. You put that in a matrix as the i, j, k unit vectors, set the translation for the cube, then you inverse this matrix. You multiply the vertices of the saved triangles by this matrix, that way you get their coordinates inside of a 0 to 1 size cube that you use as the UV coordinates. This way you have the original triangles you're projecting onto and you have UV coordinates for them (the UV coordinates are referencing the texture you're projecting). Then you rerender the saved triangles onto the scene and they overwrite the area of projection with the projected image. Now the questions that i couldn't find answers for. Is the last point right? I've never done software clipping, but it seems error prone enough, due to limited precision, that the'll be some z fighting occuring for the projected texture. Also is the way of getting UV coordinates correct?

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  • Why are SW engineering interviews disproportionately difficult?

    - by stackoverflowuser2010
    First, some background on me. I have a PhD in CS and have had jobs both as a software engineer and as an R&D research scientist, both at Very Large Corporations You Know Very Well. I recently changed jobs and interviewed for both types of jobs (as I have done in the past). My observation: SW engineer job interviews are way, way disproportionately more difficult than CS researcher job interviews, but the researcher job is higher paying, more competitive, more rewarding, more interesting, and has a higher upside. Here's a typical interview loop for researcher: Phone interview to see if my research is in alignment with the lab's researcher In-person, give presentation on my recent research for one hour (which represents maybe 9 month's worth of work), answer questions In-person one-on-one interviews with about 5 researchers, where they ask me very reasonable questions on my work/publications/patents, including: technical questions, where my work fits into related work, and how I can extend my work to new areas Here's a typical interview loop for SW engineer: Phone interview where I'm asked algorithm questions and maybe do some coding. Pretty standard. In-person interviews at the whiteboard where they drill the F*** out of you on esoteric C++ minutia (e.g. how does a polymorphic virtual function call work), algorithms (make all-pairs-shortest-path algorithm work for 1B vertices), system design (design a database load balancer), etc. This goes on for six or seven interviews. Ridiculous. Why would anyone be willing to put up with this? What is the point of asking about C++ trivia or writing code to prove yourself? Why not make the SE interview more like the researcher interview where you give a talk about what you've done? How are technical job interviews for other fields, like physics, chemistry, civil engineering, mechanical engineering?

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  • Vertex buffer acting strange? [on hold]

    - by Ryan Capote
    I'm having a strange problem, and I don't know what could be causing it. My current code is identical to how I've done this before. I'm trying to render a rectangle using VBO and orthographic projection.   My results:     What I expect: 3x3 rectangle in the top left corner   #include <stdio.h> #include <GL\glew.h> #include <GLFW\glfw3.h> #include "lodepng.h"   static const int FALSE = 0; static const int TRUE = 1;   static const char* VERT_SHADER =     "#version 330\n"       "layout(location=0) in vec4 VertexPosition; "     "layout(location=1) in vec2 UV;"     "uniform mat4 uProjectionMatrix;"     /*"out vec2 TexCoords;"*/       "void main(void) {"     "    gl_Position = uProjectionMatrix*VertexPosition;"     /*"    TexCoords = UV;"*/     "}";   static const char* FRAG_SHADER =     "#version 330\n"       /*"uniform sampler2D uDiffuseTexture;"     "uniform vec4 uColor;"     "in vec2 TexCoords;"*/     "out vec4 FragColor;"       "void main(void) {"    /* "    vec4 texel = texture2D(uDiffuseTexture, TexCoords);"     "    if(texel.a <= 0) {"     "         discard;"     "    }"     "    FragColor = texel;"*/     "    FragColor = vec4(1.f);"     "}";   static int g_running; static GLFWwindow *gl_window; static float gl_projectionMatrix[16];   /*     Structures */ typedef struct _Vertex {     float x, y, z, w;     float u, v; } Vertex;   typedef struct _Position {     float x, y; } Position;   typedef struct _Bitmap {     unsigned char *pixels;     unsigned int width, height; } Bitmap;   typedef struct _Texture {     GLuint id;     unsigned int width, height; } Texture;   typedef struct _VertexBuffer {     GLuint bufferObj, vertexArray; } VertexBuffer;   typedef struct _ShaderProgram {     GLuint vertexShader, fragmentShader, program; } ShaderProgram;   /*   http://en.wikipedia.org/wiki/Orthographic_projection */ void createOrthoProjection(float *projection, float width, float height, float far, float near)  {       const float left = 0;     const float right = width;     const float top = 0;     const float bottom = height;          projection[0] = 2.f / (right - left);     projection[1] = 0.f;     projection[2] = 0.f;     projection[3] = -(right+left) / (right-left);     projection[4] = 0.f;     projection[5] = 2.f / (top - bottom);     projection[6] = 0.f;     projection[7] = -(top + bottom) / (top - bottom);     projection[8] = 0.f;     projection[9] = 0.f;     projection[10] = -2.f / (far-near);     projection[11] = (far+near)/(far-near);     projection[12] = 0.f;     projection[13] = 0.f;     projection[14] = 0.f;     projection[15] = 1.f; }   /*     Textures */ void loadBitmap(const char *filename, Bitmap *bitmap, int *success) {     int error = lodepng_decode32_file(&bitmap->pixels, &bitmap->width, &bitmap->height, filename);       if (error != 0) {         printf("Failed to load bitmap. ");         printf(lodepng_error_text(error));         success = FALSE;         return;     } }   void destroyBitmap(Bitmap *bitmap) {     free(bitmap->pixels); }   void createTexture(Texture *texture, const Bitmap *bitmap) {     texture->id = 0;     glGenTextures(1, &texture->id);     glBindTexture(GL_TEXTURE_2D, texture);       glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);       glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, bitmap->width, bitmap->height, 0,              GL_RGBA, GL_UNSIGNED_BYTE, bitmap->pixels);       glBindTexture(GL_TEXTURE_2D, 0); }   void destroyTexture(Texture *texture) {     glDeleteTextures(1, &texture->id);     texture->id = 0; }   /*     Vertex Buffer */ void createVertexBuffer(VertexBuffer *vertexBuffer, Vertex *vertices) {     glGenBuffers(1, &vertexBuffer->bufferObj);     glGenVertexArrays(1, &vertexBuffer->vertexArray);     glBindVertexArray(vertexBuffer->vertexArray);       glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer->bufferObj);     glBufferData(GL_ARRAY_BUFFER, sizeof(Vertex) * 6, (const GLvoid*)vertices, GL_STATIC_DRAW);       const unsigned int uvOffset = sizeof(float) * 4;       glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, sizeof(Vertex), 0);     glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, sizeof(Vertex), (GLvoid*)uvOffset);       glEnableVertexAttribArray(0);     glEnableVertexAttribArray(1);       glBindBuffer(GL_ARRAY_BUFFER, 0);     glBindVertexArray(0); }   void destroyVertexBuffer(VertexBuffer *vertexBuffer) {     glDeleteBuffers(1, &vertexBuffer->bufferObj);     glDeleteVertexArrays(1, &vertexBuffer->vertexArray); }   void bindVertexBuffer(VertexBuffer *vertexBuffer) {     glBindVertexArray(vertexBuffer->vertexArray);     glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer->bufferObj); }   void drawVertexBufferMode(GLenum mode) {     glDrawArrays(mode, 0, 6); }   void drawVertexBuffer() {     drawVertexBufferMode(GL_TRIANGLES); }   void unbindVertexBuffer() {     glBindVertexArray(0);     glBindBuffer(GL_ARRAY_BUFFER, 0); }   /*     Shaders */ void compileShader(ShaderProgram *shaderProgram, const char *vertexSrc, const char *fragSrc) {     GLenum err;     shaderProgram->vertexShader = glCreateShader(GL_VERTEX_SHADER);     shaderProgram->fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);       if (shaderProgram->vertexShader == 0) {         printf("Failed to create vertex shader.");         return;     }       if (shaderProgram->fragmentShader == 0) {         printf("Failed to create fragment shader.");         return;     }       glShaderSource(shaderProgram->vertexShader, 1, &vertexSrc, NULL);     glCompileShader(shaderProgram->vertexShader);     glGetShaderiv(shaderProgram->vertexShader, GL_COMPILE_STATUS, &err);       if (err != GL_TRUE) {         printf("Failed to compile vertex shader.");         return;     }       glShaderSource(shaderProgram->fragmentShader, 1, &fragSrc, NULL);     glCompileShader(shaderProgram->fragmentShader);     glGetShaderiv(shaderProgram->fragmentShader, GL_COMPILE_STATUS, &err);       if (err != GL_TRUE) {         printf("Failed to compile fragment shader.");         return;     }       shaderProgram->program = glCreateProgram();     glAttachShader(shaderProgram->program, shaderProgram->vertexShader);     glAttachShader(shaderProgram->program, shaderProgram->fragmentShader);     glLinkProgram(shaderProgram->program);          glGetProgramiv(shaderProgram->program, GL_LINK_STATUS, &err);       if (err != GL_TRUE) {         printf("Failed to link shader.");         return;     } }   void destroyShader(ShaderProgram *shaderProgram) {     glDetachShader(shaderProgram->program, shaderProgram->vertexShader);     glDetachShader(shaderProgram->program, shaderProgram->fragmentShader);       glDeleteShader(shaderProgram->vertexShader);     glDeleteShader(shaderProgram->fragmentShader);       glDeleteProgram(shaderProgram->program); }   GLuint getUniformLocation(const char *name, ShaderProgram *program) {     GLuint result = 0;     result = glGetUniformLocation(program->program, name);       return result; }   void setUniformMatrix(float *matrix, const char *name, ShaderProgram *program) {     GLuint loc = getUniformLocation(name, program);       if (loc == -1) {         printf("Failed to get uniform location in setUniformMatrix.\n");         return;     }       glUniformMatrix4fv(loc, 1, GL_FALSE, matrix); }   /*     General functions */ static int isRunning() {     return g_running && !glfwWindowShouldClose(gl_window); }   static void initializeGLFW(GLFWwindow **window, int width, int height, int *success) {     if (!glfwInit()) {         printf("Failed it inialize GLFW.");         *success = FALSE;        return;     }          glfwWindowHint(GLFW_RESIZABLE, 0);     *window = glfwCreateWindow(width, height, "Alignments", NULL, NULL);          if (!*window) {         printf("Failed to create window.");         glfwTerminate();         *success = FALSE;         return;     }          glfwMakeContextCurrent(*window);       GLenum glewErr = glewInit();     if (glewErr != GLEW_OK) {         printf("Failed to initialize GLEW.");         printf(glewGetErrorString(glewErr));         *success = FALSE;         return;     }       glClearColor(0.f, 0.f, 0.f, 1.f);     glViewport(0, 0, width, height);     *success = TRUE; }   int main(int argc, char **argv) {          int err = FALSE;     initializeGLFW(&gl_window, 480, 320, &err);     glDisable(GL_DEPTH_TEST);     if (err == FALSE) {         return 1;     }          createOrthoProjection(gl_projectionMatrix, 480.f, 320.f, 0.f, 1.f);          g_running = TRUE;          ShaderProgram shader;     compileShader(&shader, VERT_SHADER, FRAG_SHADER);     glUseProgram(shader.program);     setUniformMatrix(&gl_projectionMatrix, "uProjectionMatrix", &shader);       Vertex rectangle[6];     VertexBuffer vbo;     rectangle[0] = (Vertex){0.f, 0.f, 0.f, 1.f, 0.f, 0.f}; // Top left     rectangle[1] = (Vertex){3.f, 0.f, 0.f, 1.f, 1.f, 0.f}; // Top right     rectangle[2] = (Vertex){0.f, 3.f, 0.f, 1.f, 0.f, 1.f}; // Bottom left     rectangle[3] = (Vertex){3.f, 0.f, 0.f, 1.f, 1.f, 0.f}; // Top left     rectangle[4] = (Vertex){0.f, 3.f, 0.f, 1.f, 0.f, 1.f}; // Bottom left     rectangle[5] = (Vertex){3.f, 3.f, 0.f, 1.f, 1.f, 1.f}; // Bottom right       createVertexBuffer(&vbo, &rectangle);            bindVertexBuffer(&vbo);          while (isRunning()) {         glClear(GL_COLOR_BUFFER_BIT);         glfwPollEvents();                    drawVertexBuffer();                    glfwSwapBuffers(gl_window);     }          unbindVertexBuffer(&vbo);       glUseProgram(0);     destroyShader(&shader);     destroyVertexBuffer(&vbo);     glfwTerminate();     return 0; }

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  • Learning to code first game, few questions on basic game development and 3D

    - by ProgrammerByDay
    I've been programming for a while, and I'm concurrently learning how to make a basic game and slimdx, and wanted to talk to someone to hopefully get a few pointers. I've read that Tetris is the "Hello, world" of game programming, which made sense to me, so I decided to give it a shot. I've been able to code up a basic version in a few hours, which I'm quite happy with, but I had a few questions about 3D programming. Right now I'm using Direct3D to do display the blocks without any textures (just colored squares). I have a data structure (2d array of bytes, where each byte denotes the presence of a block and its color) which is the "game board," and on every render() call I create a new vertex buffer of the existing squares in the game board, and draw those primitives. This feels very inefficient, and I wondering what would be the idiomatic way of doing this in a 3D world, with matrix/rotations/translation operations. I know 3D is overkill for such a project, but I want to learn any 3d concepts that I can while I'm doing it. I understand that what you'd usually want to do is keep the same vertices/vertex buffers but manipulate them with matrices to achieve rotations/translations, etc. To do so, I assume what would happen is I'd have one vertex buffer for the "active" piece, since that'll be constantly rotated and moved, and have one vertex buffer for the frozen pieces on the bottom of the board, which is pretty much stationary, but will need to be changed/recreated when the active piece becomes frozen. Right now I'm just clearing and redrawing on every render call, which seems like the easiest way to do things, although I wonder if there's a more efficient way to deal with changes. Obviously there are a lot of questions I'm asking here, but if you can even just point me a step or two ahead in terms of how I should be thinking, it'd be great. Thanks

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  • Orthographic Projection Issue

    - by Nick
    I have a problem with my Ortho Matrix. The engine uses the perspective projection fine but for some reason the Ortho matrix is messed up. (See screenshots below). Can anyone understand what is happening here? At the min I am taking the Projection matrix * Transform (Translate, rotate, scale) and passing to the Vertex shader to multiply the Vertices by it. VIDEO Shows the same scene, rotating on the Y axis. http://youtu.be/2feiZAIM9Y0 void Matrix4f::InitOrthoProjTransform(float left, float right, float top, float bottom, float zNear, float zFar) { m[0][0] = 2 / (right - left); m[0][1] = 0; m[0][2] = 0; m[0][3] = 0; m[1][0] = 0; m[1][1] = 2 / (top - bottom); m[1][2] = 0; m[1][3] = 0; m[2][0] = 0; m[2][1] = 0; m[2][2] = -1 / (zFar - zNear); m[2][3] = 0; m[3][0] = -(right + left) / (right - left); m[3][1] = -(top + bottom) / (top - bottom); m[3][2] = -zNear / (zFar - zNear); m[3][3] = 1; } This is what happens with Ortho Matrix: This is the Perspective Matrix:

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  • Why isn't my lighting working properly? Are my normals messed up?

    - by Radek Slupik
    I'm relatively new to OpenGL and I am trying to draw a 3D model (loaded from a 3ds file using lib3ds) using OpenGL with lighting, but about half of it is drawn in black. I set up the light as such: glEnable(GL_LIGHTING); glShadeModel(GL_SMOOTH); GLfloat ambientColor[] = {0.2f, 0.2f, 0.2f, 1.0f}; glLightModelfv(GL_LIGHT_MODEL_AMBIENT, ambientColor); glEnable(GL_LIGHT0); GLfloat lightColor0[] = {1.0f, 1.0f, 1.0f, 1.0f}; GLfloat lightPos0[] = {4.0f, 0.0f, 8.0f, 0.0f}; glLightfv(GL_LIGHT0, GL_DIFFUSE, lightColor0); glLightfv(GL_LIGHT0, GL_POSITION, lightPos0); The model is in a VBO and drawn using glDrawArrays. The normals are in a separate VBO, and the normals are calculated using lib3ds_mesh_calculate_vertex_normals: std::vector<std::array<float, 3>> normals; for (std::size_t i = 0; i < model->nmeshes; ++i) { auto& mesh = *model->meshes[i]; std::vector<float[3]> vertex_normals(mesh.nfaces * 3); lib3ds_mesh_calculate_vertex_normals(&mesh, vertex_normals.data()); for (std::size_t j = 0; j < mesh.nfaces; ++j) { auto& face = mesh.faces[j]; normals.push_back(make_array(vertex_normals[j])); } } glBindBuffer(GL_ARRAY_BUFFER, normal_vbo_); glBufferData(GL_ARRAY_BUFFER, normals.size() * sizeof(decltype(normals)::value_type), normals.data(), GL_STATIC_DRAW); The problem isn't the vertices; the model is drawn correctly when drawing it as a wireframe. I also fixed the normals in Blender using controlN. What could be the problem? Should I store the normals in a different order?

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  • Tessellating to a curve?

    - by Avi
    I'm creating a game engine, and I'm trying to define a 3D model format I want to use. I haven't come across a format that quite does what I want. My game engine assumes a shader model 5+ environment. By the time I'm finished with it, that won't be a very unreasonable requirement. Because it assumes such a modern environment, I'm going to try and exploit tessellation. The most popular way, it seems, to procedurally increase geometry through tessellation is to tessellate to a height map. This works for a lot of things, but has limitations in that height maps still use up VRAM and also only have finite scalability. So I want to be able to use curves to define what a mesh should tessellate to. The thing is, I have no idea what definition of curves I should use, how I should store it, and how I should tessellate to it. Do I use NURBS curves? Bezier? Hermite? And once I figure that out, is there an algorithm to determine how the tessellation shader should produce and move vertices to match the curve as closely as possible? Is the infinite scalability and lower memory usage when compared to height maps worth the added computational complexity? I'm sorry I'm kind if ignorant as to these matters. I just don't know where to start.

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