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Thread: Sampling neighbouring texels (Fetch4/Gather4)

  1. #1
    Junior Member Regular Contributor
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    Aug 2007
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    107

    Sampling neighbouring texels (Fetch4/Gather4)

    Hi all. I currently use 4 function calls to sample the neightbouring texels (it is not for shadow mapping). I read that ATI has a feature called Fetch4 that is able to fetch these texels in a single call from a 1-component texture. From searching around I can understand that this feature is mandatory in DX10.1 (SM4.1) and called Gather4. It does not look like the same functionality is possible on a NVidia 8800GTS-512 (DX10/SM4). In fact it does not look like it is possible on any current Nvidia GPU. Is this correct? One can perhaps assume it will be supported in GF9900 comming out later this year (DX10.1)?!
    kind regards,
    Nicolai de Haan

  2. #2
    Member Regular Contributor
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    Re: Sampling neighbouring texels (Fetch4/Gather4)

    AFAIK, the Gather4 is supported only by ATI Radeon 3XXX cards(3870,3650,etc) and the S3 Chrome 430GT, both under DX10.1 and Vista. However, if you need it for a depth map, the old ATI's Fetch4 should work ok.

    The GeForces 8 or 9 don't support it directly, but you could use their built-in hardware PCF to achieve a similar result if you use depth textures.

    Finally, you could wait and see if the OpenGL 3.0 model exposes something like the gather4 ( if some day is released... )

  3. #3
    Junior Member Regular Contributor
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    Aug 2007
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    107

    Re: Sampling neighbouring texels (Fetch4/Gather4)

    Thanks for your post. I only have a NVidia card so maybe I should try and look into NV PCF for depth textures and see if it can be used/exploited for something that is not shadow mapping.
    kind regards,
    Nicolai de Haan

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