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  1. You need to look at the contents of the memory...

    You need to look at the contents of the memory which should be filled by glReadPixels() to determine which part isn't working (the reading or the saving). Also check for errors.

    Also, note that a...
  2. If you want texture coordinates interpolated in...

    If you want texture coordinates interpolated in screen space, add the noperspective qualifier to the variable.

    If you're having issues with depth precision, try increasing the distance to the near...
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    Not that I know of. There are some complete BLAS...

    Not that I know of. There are some complete BLAS implementations for OpenCL or for specific GPUs, but not so much for LAPACK, and nothing using GLSL (however, you can pass GPU-side data between GLSL...
  4. One thing that's wrong is that you're updating...

    One thing that's wrong is that you're updating the buffers before appending to the vectors, so the last point added isn't in the buffer. But it is included in the value of g_indexes.size(), so the...
  5. The *DrawElements() functions need an EBO....

    The *DrawElements() functions need an EBO. glMultiDrawArrays() doesn't. You only need one VAO and VBO.


    For GL_LINES, the indices would be 0,1,1,2,2,3,... etc, with the last index of one segment...
  6. Note that the *_ADJACENCY primitive types are...

    Note that the *_ADJACENCY primitive types are only useful if you're using a geometry shader. Otherwise, using GL_LINE_STRIP_ADJACENCY will simply cause the first and last segments in each strip to be...
  7. Modern hardware uses actual branches for...

    Modern hardware uses actual branches for conditions which are dynamically uniform, i.e. where the result is the same for all shader invocations which are executed in parallel.

    On hardware lacking...
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    glMultiDrawElementsBaseVertex() requires OpenGL...

    glMultiDrawElementsBaseVertex() requires OpenGL 3.2.


    Instancing is used if you want to draw multiple copies of the same object. The copies don't need to be identical in every regard (there...
  9. In that case, OpenGL isn't of much use to you....

    In that case, OpenGL isn't of much use to you. Either use the platform's native windowing API, or if you want cross-platform something like SDL.
  10. So the yaw is about the local vertical axis,...

    So the yaw is about the local vertical axis, after pitch has been applied.

    If you want them in a different order, you can either change the order in the quat() constructor then apply a suitable...
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    Does the application provide a framework for...

    Does the application provide a framework for plug-ins to use OpenGL? Or at least for them to use the windowing API? Windowing APIs generally don't lend themselves to being used by multiple subsystems...
  12. string::reserve() only reserves space; the length...

    string::reserve() only reserves space; the length will still be zero. Use e.g.


    log.assign(length, '\0');

    to enlarge the string. Or just create the string at the appropriate size:

    ...
  13. Multiple passes with transform feedback. Start...

    Multiple passes with transform feedback. Start with a set of vertex arrays containing a single identity matrix. Each pass uses instanced rendering to generate N copies of the data, each copy...
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    The intended purpose of the vertex shader is to...

    The intended purpose of the vertex shader is to assign the output variables which are interpolated to provide the fragment shader's inputs. Initially that was all it could do, but later versions...
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    The best solution is to just pass the colour...

    The best solution is to just pass the colour index for each row as a uniform array (or 1D texture).

    Making the fragment shader do this is rather awkward, given the way that fragment shaders work....
  16. The type passed to glBeginTransformFeedback()...

    The type passed to glBeginTransformFeedback() must match the type of primitives generated by draw calls. If no geometry shader is active, then glBeginTransformFeedback(GL_POINTS) requires all draw...
  17. Yes. in float tff_in[12] declares 12 separate...

    Yes. in float tff_in[12] declares 12 separate attributes, ttf_in[0] to ttf_in[11] inclusive. Those attributes will be consecutively numbered, so you'd only need to call glGetAttribLocation("ttf_in")...
  18. That would result in 12 separate attributes. So...

    That would result in 12 separate attributes. So you'd need 12 glVertexAttribPointer() calls. Vertex shader inputs cannot be structures; you'd need to either use 4 separate variables, or an array of 4...
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    What is your issue exactly? A normal map gives...

    What is your issue exactly?

    A normal map gives you a normal vector at any given point on the surface. But that normal vector is typically for a flat, horizontal surface (i.e. a normal of (0,0,1)...
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    According to the glBeginTransformFeedback()...

    According to the glBeginTransformFeedback() reference page:



    The call to glTransformFeedbackVaryings() in the code you've shown has a count of zero, which would correspond to the last of the...
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    A matrix whose columns are the world-space T,B,N...

    A matrix whose columns are the world-space T,B,N vectors transforms from tangent space to world space. Its inverse (which is the same as the transpose provided that the matrix is orthonormal)...
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    It just needs to be bound. In OpenGL 3+ core...

    It just needs to be bound. In OpenGL 3+ core profile, all state relating to attribute arrays (plus the current element array buffer binding) is stored in the currently-bound VAO. It's an error to...
  23. You're missing a negative sign for the bottom...

    You're missing a negative sign for the bottom parameter.
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    No. Rendering to a texture requires using a FBO,...

    No. Rendering to a texture requires using a FBO, although using a FBO doesn't always involve textures (renderbuffers can be used instead).

    I said "render to texture" rather than FBOs because I...
  25. This isn't going to support anything above OpenGL...

    This isn't going to support anything above OpenGL 2.1, and that can't be changed via software. If this a desktop system with a PCIe slot, you can install a discrete graphics card. Even a cheap card...
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