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  1. If you're using glCopyTexImage, simply give it a...

    If you're using glCopyTexImage, simply give it a compressed <internalformat>. Then use glGetCompressedTexImage to retrieve the bytes.



    Some platforms have solutions for cross-process surface...
  2. That man page is wrong; smoothstep() has been...

    That man page is wrong; smoothstep() has been there since the very beginning (100, 110 and 120.)
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    Your GPU supports GL 4.1...

    Your GPU supports GL 4.1 in OS X 10.9.
    But only if you opt in to Core Profile.

    You'll have to figure out how to do that in Java.




    Many features of GL3.x (fbos & blits, float & integer...
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    Read ARB_shader_draw_parameters...

    Read ARB_shader_draw_parameters.
  5. Colors in GL are typically in [0.0...1.0], not...

    Colors in GL are typically in [0.0...1.0], not [0.0...255.0].
  6. Very old (~2006) desktop GPUs and most current...

    Very old (~2006) desktop GPUs and most current phone GPUs can't filter 32-bit floats. Try RG16F.


    Do an experiment to confirm your suspicions: make a two-pixel texture with black and white, and...
  7. Start by reading the "Standard Uniform Block...

    Start by reading the "Standard Uniform Block Layout" section in the spec.



    After reading the spec, you should see that your struct isn't really 16 floats. You can introspect it to confirm,...
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    You've uploaded GLushorts, but declared floats. ...

    You've uploaded GLushorts, but declared floats. So your actual index data is [0000 0000 0000 3f80], which draws one degenerate triangle, and then dereferences far outside of your allocated vbo (i.e....
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    Setting clipspace gl_Position.w = 0.0 means that...

    Setting clipspace gl_Position.w = 0.0 means that all NDC xyz = infinity.
  10. You'll need to prepend "#version 100". ...and...

    You'll need to prepend "#version 100".

    ...and there's no provision for any ES-specific #extensions...
  11. That's your answer. If your implementation...

    That's your answer. If your implementation doesn't expose textureLod (i.e. via EXT_shader_texture_lod in ES2 on iOS) then you can't do it.

    For debugging only (i.e. visualizing unfolded cube map...
  12. If you're asking "why is the API the way it is"...

    If you're asking "why is the API the way it is" -- I can't answer that. I agree it isn't very easy to use.



    But if you're asking "how do I query the format of the VAO" -- the answer is to use...
  13. You're making the faulty assumption that the VAO...

    You're making the faulty assumption that the VAO format and the shader inputs are the same. There is absolutely no such guarantee.

    A vertex array can contain i.e. two floats, and the...
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    How about: "when you want to port your code to a...

    How about: "when you want to port your code to a phone."
  15. The point of "indirect" is that the draw...

    The point of "indirect" is that the draw arguments come from a buffer object.

    This is useful if your content is *generated on the GPU*, i.e. via transform feedback, or compute shaders.

    A simple...
  16. Vertex transform is inherently one-vert-in,...

    Vertex transform is inherently one-vert-in, one-vert-out. There is no communication between vertices (but parallel execution potential is high.)

    Min/Max requires comparing all N vertices, so you...
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    The "shared" and "std140" layout qualifiers...

    The "shared" and "std140" layout qualifiers should defeat any compiler optimizations that would eliminate unused block members. But you do need to declare the blocks identically in all the programs...
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    Your code fragment "works" here (on OSX 10.9.3,...

    Your code fragment "works" here (on OSX 10.9.3, Nvidia, Intel, and software renderers.) It produces "10" for all mipmap texels.




    You should double-check what you expect to happen. Integer...
  19. In GL, I would advise you to introspect the...

    In GL, I would advise you to introspect the texture via glGetTexLevelParameter, to verify it is really as you expect (i.e. the subimage dimensions are within the actual defined dimensions, and the...
  20. What were the arguments to the original...

    What were the arguments to the original glTexImage2D (or glTexStorage2D) call that defined that texture?
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    Read the rasterization rules. It depends what...

    Read the rasterization rules. It depends what type of primitive you're drawing.
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    You forgot to set MIN_FILTER. It's the same very...

    You forgot to set MIN_FILTER. It's the same very common mistake everyone makes.
  23. Debug tips: 1) OpenGL does not know anything...

    Debug tips:

    1) OpenGL does not know anything about "files". When you compile a shader, you pass a pointer to the shader text. Your file loading code is responsible for producing that pointer....
  24. Use async MapBuffer...

    Use async MapBuffer to avoid stalls. Read the wiki.
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    You previously mentioned you're using Xcode. Let...

    You previously mentioned you're using Xcode. Let me save you a lot of time and point you at an example of setting up the debugger.

    If your case, if you use the debugger you'll find you're calling...
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