tree df65513b64cde80c81072648544e1ba9f641f5d0
parent 201419404c1660c9b5c993f68bdc7677c02967fc
author Shahbaz Youssefi <syoussefi@chromium.org> 1565203452 -0400
committer Commit Bot <commit-bot@chromium.org> 1565811949 +0000

Vulkan: Emulate subgroup ops in seamful cubemap emulation

Where subgroup ops are not available, they are emulated as such:

Code with subgroup ops:

    float lH = subgroupQuadSwapHorizontal(layer);
    float lV = subgroupQuadSwapVertical(layer);
    float lD = subgroupQuadSwapDiagonal(layer);

    bool isHelperH = subgroupQuadSwapHorizontal(gl_HelperInvocation);
    bool isHelperV = subgroupQuadSwapVertical(gl_HelperInvocation);

    if (gl_HelperInvocation)
    {
        layer = !isHelperH ? lH : !isHelperV ? lV : lD;
    }

Emulated code:

    float nonHelperLayer = gl_HelperInvocation ? 0.0 : layer;
    float lH = abs(dFdxFine(nonHelperLayer));
    float lV = abs(dFdyFine(nonHelperLayer));
    float lD = abs(dFdxFine(lV));

    float isHelperDiffH = abs(dFdxFine(float(gl_HelperInvocation)));
    bool isNonHelperH = isHelperDiffH > 0.5;

    float isHelperDiffV = abs(dFdyFine(float(gl_HelperInvocation)));
    bool isNonHelperV = isHelperDiffV > 0.5;

    if (gl_HelperInvocation)
    {
        layer = isNonHelperH ? lH : isNonHelperV ? lV : lD;
    }

Both paths are supported as on nvidia devices the emulated code
misbehaves.  This change therefore effectively only enables seamful cube
map emulation on Android where subgroup operations are not supported.

Bug: angleproject:3243
Bug: angleproject:3732
Change-Id: I9664d9760756758748183eb121c626f176789f3a
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1742222
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>