[Webkit-unassigned] [Bug 137793] Calling glReadPixels with BGRA format on an NVIDIA machine with an opaque context returns the wrong alpha values.

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=137793

--- Comment #8 from Dean Jackson <dino at apple.com> ---
Comment on attachment 240001
  --> https://bugs.webkit.org/attachment.cgi?id=240001
patch

View in context: https://bugs.webkit.org/attachment.cgi?id=240001&action=review

> Source/WebCore/platform/graphics/opengl/GraphicsContext3DOpenGL.cpp:72
> +        ::glReadPixels(x, y, width, height, GL_RGBA, GL_UNSIGNED_INT_8_8_8_8_REV, pixels);
> +        int totalBytes = width * height * 4;
> +        for (int i = 0; i < totalBytes; i += 4)

e.g.
vImage_Buffer src;
src.height = height;
src.width = width;
src.rowBytes = srcBytesPerRow;
src.data = srcRows;

vImage_Buffer dest;
dest.height = height;
dest.width = width;
dest.rowBytes = destBytesPerRow;
dest.data = destRows;

// Swap pixel channels from BGRA to RGBA.
const uint8_t map[4] = { 2, 1, 0, 3 };
vImagePermuteChannels_ARGB8888(&src, &dest, map, kvImageNoFlags);

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