Expected result when overflowing a lowp variable?

This topic contains 2 replies, has 2 voices, and was last updated by  scratt 6 years, 8 months ago.

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  • #30452

    scratt
    Member

    I am simply curious about this…

    On the iPhone Simulator if I use a lowp variable to accumulate a colour result, in something like a “god ray” or blur shader I get a saturated result, ultimately. No matter how many reasonable iterations I carry out.

    On iOS devices, however, I get a ‘0’ result, which I can only assume is because of some kind of overflow situation. Replacing the lowp with a medium solves the problem.

    I don’t mind which happens, and can see reasons for either.

    I am just curious as to what the “expected” result is from Imagination’s perspective…scratt2011-02-16 09:20:44

    #34750

    Xmas
    Member

    You should get a saturated result. Can you post the shader you are using?

    #34751

    scratt
    Member

    Sorry, that particular iteration of the fragment shader went in the bin.

    It is fairly easy to replicate, and is basically a lowp vec3 (initially defined outside of a loop) accumulating lots of lowp vec3 texture reads inside that loop with about 20 – 40 iterations.

    I have filed a bug report with Apple, and been asked for a reproducer.

    When I do that for Apple I will put a copy in this thread also.scratt2011-02-18 04:46:09

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