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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/174855">174855</a></dd>
<dt>Author</dt> <dd>roger_fong@apple.com</dd>
<dt>Date</dt> <dd>2014-10-17 17:25:08 -0700 (Fri, 17 Oct 2014)</dd>
</dl>
<h3>Log Message</h3>
<pre>Calling glReadPixels with BGRA format on an NVIDIA machine with an opaque context returns the wrong alpha values.
https://bugs.webkit.org/show_bug.cgi?id=137793.
<rdar://problem/15408133>
Reviewed by Dean Jackson.
This fixes conformance test context/context-attribute-preserve-drawing-buffer.html.
* platform/graphics/opengl/GraphicsContext3DOpenGL.cpp:
(WebCore::GraphicsContext3D::readPixelsAndConvertToBGRAIfNecessary):
On an NVIDIA machine, when the context has alpha turned off, call glReadPixels with RGBA format and then convert to RGBA.</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceWebCoreChangeLog">trunk/Source/WebCore/ChangeLog</a></li>
<li><a href="#trunkSourceWebCoreplatformgraphicsopenglGraphicsContext3DOpenGLcpp">trunk/Source/WebCore/platform/graphics/opengl/GraphicsContext3DOpenGL.cpp</a></li>
</ul>
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<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceWebCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/ChangeLog (174854 => 174855)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/ChangeLog 2014-10-18 00:21:40 UTC (rev 174854)
+++ trunk/Source/WebCore/ChangeLog 2014-10-18 00:25:08 UTC (rev 174855)
</span><span class="lines">@@ -1,3 +1,17 @@
</span><ins>+2014-10-16 Roger Fong <roger_fong@apple.com>
+
+ Calling glReadPixels with BGRA format on an NVIDIA machine with an opaque context returns the wrong alpha values.
+ https://bugs.webkit.org/show_bug.cgi?id=137793.
+ <rdar://problem/15408133>
+
+ Reviewed by Dean Jackson.
+
+ This fixes conformance test context/context-attribute-preserve-drawing-buffer.html.
+
+ * platform/graphics/opengl/GraphicsContext3DOpenGL.cpp:
+ (WebCore::GraphicsContext3D::readPixelsAndConvertToBGRAIfNecessary):
+ On an NVIDIA machine, when the context has alpha turned off, call glReadPixels with RGBA format and then convert to RGBA.
+
</ins><span class="cx"> 2014-10-17 Chris Dumez <cdumez@apple.com>
</span><span class="cx">
</span><span class="cx"> Use is<>() / downcast<>() for all SVG RenderObjects
</span></span></pre></div>
<a id="trunkSourceWebCoreplatformgraphicsopenglGraphicsContext3DOpenGLcpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/platform/graphics/opengl/GraphicsContext3DOpenGL.cpp (174854 => 174855)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/platform/graphics/opengl/GraphicsContext3DOpenGL.cpp 2014-10-18 00:21:40 UTC (rev 174854)
+++ trunk/Source/WebCore/platform/graphics/opengl/GraphicsContext3DOpenGL.cpp 2014-10-18 00:25:08 UTC (rev 174855)
</span><span class="lines">@@ -44,6 +44,10 @@
</span><span class="cx"> #include <wtf/MainThread.h>
</span><span class="cx"> #include <wtf/text/CString.h>
</span><span class="cx">
</span><ins>+#if USE(ACCELERATE)
+#include <Accelerate/Accelerate.h>
+#endif
+
</ins><span class="cx"> #if PLATFORM(IOS)
</span><span class="cx"> #import <OpenGLES/ES2/glext.h>
</span><span class="cx"> // From <OpenGLES/glext.h>
</span><span class="lines">@@ -65,7 +69,32 @@
</span><span class="cx">
</span><span class="cx"> void GraphicsContext3D::readPixelsAndConvertToBGRAIfNecessary(int x, int y, int width, int height, unsigned char* pixels)
</span><span class="cx"> {
</span><del>- ::glReadPixels(x, y, width, height, GL_BGRA, GL_UNSIGNED_INT_8_8_8_8_REV, pixels);
</del><ins>+ // NVIDIA drivers have a bug where calling readPixels in BGRA can return the wrong values for the alpha channel when the alpha is off for the context.
+ if (!m_attrs.alpha && getExtensions()->isNVIDIA()) {
+ ::glReadPixels(x, y, width, height, GL_RGBA, GL_UNSIGNED_BYTE, pixels);
+#if USE(ACCELERATE)
+ vImage_Buffer src;
+ src.height = height;
+ src.width = width;
+ src.rowBytes = width*4;
+ src.data = pixels;
+
+ vImage_Buffer dest;
+ dest.height = height;
+ dest.width = width;
+ dest.rowBytes = width*4;
+ dest.data = pixels;
+
+ // Swap pixel channels from RGBA to BGRA.
+ const uint8_t map[4] = { 2, 1, 0, 3 };
+ vImagePermuteChannels_ARGB8888(&src, &dest, map, kvImageNoFlags);
+#else
+ int totalBytes = width * height * 4;
+ for (int i = 0; i < totalBytes; i += 4)
+ std::swap(pixels[i], pixels[i + 2]);
+#endif
+ } else
+ ::glReadPixels(x, y, width, height, GL_BGRA, GL_UNSIGNED_INT_8_8_8_8_REV, pixels);
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> void GraphicsContext3D::validateAttributes()
</span></span></pre>
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