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  1. Thread: OpenGL 3 Updates

    by Humus
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    Re: OpenGL 3 Updates

    To further elaborate, one important difference between ARB_fp and what the hardware really does is that ARB_fp doesn't take the mini-alu into account that all R300-R580 hardware is equiped with, nor...
  2. Thread: OpenGL 3 Updates

    by Humus
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    17,155,586

    Re: OpenGL 3 Updates

    These extensions are very generic and at least on ATI cards they pass through the same optimizer as the GLSL ones, and DX shaders too for that matter. I'd say they aren't very close to hardware at...
  3. Thread: OpenGL 3 Updates

    by Humus
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    Re: OpenGL 3 Updates

    But all 3.0 targetted hardware supports discard, hence alpha test is not neccesary. OpenGL specifications have traditionally been very forwardlooking. OpenGL 1.0 was written when hardware barely...
  4. Thread: OpenGL 3 Updates

    by Humus
    Replies
    1,723
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    17,155,586

    Re: OpenGL 3 Updates

    I don't have any up to date plans as I'm not working there anymore, but the GL driver used in Vista (which is a total from scratch rewrite) works in XP too for all hardware R300 and up. However, it's...
  5. Thread: OpenGL 3 Updates

    by Humus
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    17,155,586

    Re: OpenGL 3 Updates

    The most evil operation is depth output. It not only kills both hi-z and early-z, it also kills z-compression and thusly negatively affect performance of later rendering passes to the same screen...
  6. Thread: OpenGL 3 Updates

    by Humus
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    17,155,586

    Re: OpenGL 3 Updates

    Fine, I was talking on an algoritmic level. If your algoritm uses one, it can be adapted to the other, but it may require more work to work around the limitations of alpha test.



    Which would be...
  7. Thread: OpenGL 3 Updates

    by Humus
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    1,723
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    17,155,586

    Re: OpenGL 3 Updates

    By the same logic dynamic branching should not be used because the branch logic may take an opcode or two, so we should just select the result at the end of the shader instead! I'm sure you can come...
  8. Thread: OpenGL 3 Updates

    by Humus
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    17,155,586

    Re: OpenGL 3 Updates

    Why would an IHV care if your test is equivalent to an alpha test?



    No IHV would ever try to convert a discard into an alpha test. However, an IHV might very well try to pull the test as early...
  9. Thread: OpenGL 3 Updates

    by Humus
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    17,155,586

    Re: OpenGL 3 Updates

    I assume you're talking about ATI, but GL_EXT_packed_depth_stencil is supported already. At least it's in my extension list. Haven't tried to use it myself though.
  10. Thread: OpenGL 3 Updates

    by Humus
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    17,155,586

    Re: OpenGL 3 Updates

    This is trivial to implement with discard:

    gl_FragColor = ...;
    if (gl_FragColor.a < ref) discard;



    Well, you can implement any function you want though just by computing a boolean result to...
  11. Thread: OpenGL 3 Updates

    by Humus
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    17,155,586

    Re: OpenGL 3 Updates

    And in fact, you can do this already in Compressonator. You can specify the weighting between the channels. I've only needed to use that once, but boosting importance of blue removed the banding in a...
  12. Thread: OpenGL 3 Updates

    by Humus
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    17,155,586

    Re: OpenGL 3 Updates

    It's not the same, but everything you can do with alpha test can be done with discard, and vice versa.



    What depends on the GPU? Fragment kills are well defined.



    Still hardware, but it...
  13. Thread: OpenGL 3 Updates

    by Humus
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    Views
    17,155,586

    Re: OpenGL 3 Updates

    Alpha test is the redundant feature. It's less flexible and offers no advantage of shader controlled fragment kills. With alpha test you burn an output channel that could be used for something...
  14. Thread: OpenGL 3 Updates

    by Humus
    Replies
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    Views
    17,155,586

    Re: OpenGL 3 Updates

    No, it's faster to kill fragments in the shader. I'm not aware of any reason why alpha test should be faster. Alpha test forces the shader to be executed in full. With discard it can be optimized to...
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