[Webkit-unassigned] [Bug 137793] New: Don't use BGRA format when reading rendering results

[bugzilla-daemon at webkit.org]

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

            Bug ID: 137793
           Summary: Don't use BGRA format when reading rendering results
    Classification: Unclassified
           Product: WebKit
           Version: 528+ (Nightly build)
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebGL
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: roger_fong at apple.com

When we call readPixels from the WebGLRenderingContext note that we spit out an error if GL_BGRA format is used.
However, we for some reason use this format when reading the rendering the results for the purposes of either reading the rendering results into an ImageData or a canvas. 
This color format seems to fail specifically fail on NVIDIA cards and in particular the alpha channel can be read incorrectly when the alpha is off for the context. However, I will make a blanket change here for all devices and context attribute settings for alpha to be consistent with WebGLRenderingContext::readPixels which does the following:

    switch (format) {
    case GraphicsContext3D::ALPHA:
    case GraphicsContext3D::RGB:
    case GraphicsContext3D::RGBA:
        break;
    default:
        synthesizeGLError(GraphicsContext3D::INVALID_ENUM, "readPixels", "invalid format");
        return;
    }

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