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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/212082">212082</a></dd>
<dt>Author</dt> <dd>carlosgc@webkit.org</dd>
<dt>Date</dt> <dd>2017-02-09 23:57:04 -0800 (Thu, 09 Feb 2017)</dd>
</dl>
<h3>Log Message</h3>
<pre>Merge <a href="http://trac.webkit.org/projects/webkit/changeset/211967">r211967</a> - [GTK] scroll with transparent background not repainted after scrollY >= 32768
https://bugs.webkit.org/show_bug.cgi?id=154283
Reviewed by Carlos Garcia Campos.
Due to a limitation of the pixman backend, which uses 16 bits to hold signed integers, cairo is
not able to draw anything when using transformation matrices with values bigger than 32768. When
drawing patterns into large pages, the matrices values can overflow those 16 bits, so cairo doesn't
draw anything in, which causes the reported transparent backgrounds.
The patch modifies the transformation matrices both from the current context and the pattern we
are painting, to avoid them to hold values that cannot stored in 16 bits.
There's still the possibility that this happens, but it would require using a pattern with a size
bigger than 32768.
Based on a previous patch by Gwang Yoon Hwang <yoon@igalia.com>.
No new tests.
* platform/graphics/cairo/CairoUtilities.cpp:
(WebCore::drawPatternToCairoContext):</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#releasesWebKitGTKwebkit214SourceWebCoreChangeLog">releases/WebKitGTK/webkit-2.14/Source/WebCore/ChangeLog</a></li>
<li><a href="#releasesWebKitGTKwebkit214SourceWebCoreplatformgraphicscairoCairoUtilitiescpp">releases/WebKitGTK/webkit-2.14/Source/WebCore/platform/graphics/cairo/CairoUtilities.cpp</a></li>
</ul>
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<div id="patch">
<h3>Diff</h3>
<a id="releasesWebKitGTKwebkit214SourceWebCoreChangeLog"></a>
<div class="modfile"><h4>Modified: releases/WebKitGTK/webkit-2.14/Source/WebCore/ChangeLog (212081 => 212082)</h4>
<pre class="diff"><span>
<span class="info">--- releases/WebKitGTK/webkit-2.14/Source/WebCore/ChangeLog 2017-02-10 07:53:14 UTC (rev 212081)
+++ releases/WebKitGTK/webkit-2.14/Source/WebCore/ChangeLog 2017-02-10 07:57:04 UTC (rev 212082)
</span><span class="lines">@@ -1,3 +1,28 @@
</span><ins>+2017-02-09 Miguel Gomez <magomez@igalia.com>
+
+ [GTK] scroll with transparent background not repainted after scrollY >= 32768
+ https://bugs.webkit.org/show_bug.cgi?id=154283
+
+ Reviewed by Carlos Garcia Campos.
+
+ Due to a limitation of the pixman backend, which uses 16 bits to hold signed integers, cairo is
+ not able to draw anything when using transformation matrices with values bigger than 32768. When
+ drawing patterns into large pages, the matrices values can overflow those 16 bits, so cairo doesn't
+ draw anything in, which causes the reported transparent backgrounds.
+
+ The patch modifies the transformation matrices both from the current context and the pattern we
+ are painting, to avoid them to hold values that cannot stored in 16 bits.
+
+ There's still the possibility that this happens, but it would require using a pattern with a size
+ bigger than 32768.
+
+ Based on a previous patch by Gwang Yoon Hwang <yoon@igalia.com>.
+
+ No new tests.
+
+ * platform/graphics/cairo/CairoUtilities.cpp:
+ (WebCore::drawPatternToCairoContext):
+
</ins><span class="cx"> 2017-02-08 Miguel Gomez <magomez@igalia.com>
</span><span class="cx">
</span><span class="cx"> [GTK] Reduce TiledBackingStore tile coverage when on memory pressure state
</span></span></pre></div>
<a id="releasesWebKitGTKwebkit214SourceWebCoreplatformgraphicscairoCairoUtilitiescpp"></a>
<div class="modfile"><h4>Modified: releases/WebKitGTK/webkit-2.14/Source/WebCore/platform/graphics/cairo/CairoUtilities.cpp (212081 => 212082)</h4>
<pre class="diff"><span>
<span class="info">--- releases/WebKitGTK/webkit-2.14/Source/WebCore/platform/graphics/cairo/CairoUtilities.cpp 2017-02-10 07:53:14 UTC (rev 212081)
+++ releases/WebKitGTK/webkit-2.14/Source/WebCore/platform/graphics/cairo/CairoUtilities.cpp 2017-02-10 07:57:04 UTC (rev 212082)
</span><span class="lines">@@ -201,8 +201,28 @@
</span><span class="cx"> cairo_pattern_t* pattern = cairo_pattern_create_for_surface(image);
</span><span class="cx"> cairo_pattern_set_extend(pattern, CAIRO_EXTEND_REPEAT);
</span><span class="cx">
</span><ins>+ // Cairo cannot convert a cairo_matrix to a Pixman's matrix if any of its components is bigger than maximum int size of Pixman.
+ // With this condition, Cairo gives up to draw given pattern entirely. To workaround this problem, we reduce the coordinate
+ // space by translating CTM and destRect.
+ cairo_matrix_t ctm;
+ cairo_get_matrix(cr, &ctm);
+ double dx = 0, dy = 0;
+ cairo_matrix_transform_point(&ctm, &dx, &dy);
+ double xScale = 1, yScale = 1;
+ cairo_matrix_transform_distance(&ctm, &xScale, &yScale);
+
+ dx = std::trunc(-dx / tileRect.width()) * tileRect.width() / xScale;
+ dy = std::trunc(-dy / tileRect.height()) * tileRect.height() / yScale;
+ cairo_translate(cr, dx, dy);
+
+ FloatRect adjustedDestRect(destRect);
+ adjustedDestRect.move(-dx, -dy);
+
+ // Again, we need to reduce the coordinate of the transformation matrix we are using for the pattern.
</ins><span class="cx"> cairo_matrix_t patternMatrix = cairo_matrix_t(patternTransform);
</span><del>- cairo_matrix_t phaseMatrix = {1, 0, 0, 1, phase.x() + tileRect.x() * patternTransform.a(), phase.y() + tileRect.y() * patternTransform.d()};
</del><ins>+ dx = phase.x() - std::trunc(phase.x() / tileRect.width()) * tileRect.width();
+ dy = phase.y() - std::trunc(phase.y() / tileRect.height()) * tileRect.height();
+ cairo_matrix_t phaseMatrix = {1, 0, 0, 1, dx + tileRect.x() * patternTransform.a(), dy + tileRect.y() * patternTransform.d()};
</ins><span class="cx"> cairo_matrix_t combined;
</span><span class="cx"> cairo_matrix_multiply(&combined, &patternMatrix, &phaseMatrix);
</span><span class="cx"> cairo_matrix_invert(&combined);
</span><span class="lines">@@ -211,7 +231,7 @@
</span><span class="cx"> cairo_set_operator(cr, op);
</span><span class="cx"> cairo_set_source(cr, pattern);
</span><span class="cx"> cairo_pattern_destroy(pattern);
</span><del>- cairo_rectangle(cr, destRect.x(), destRect.y(), destRect.width(), destRect.height());
</del><ins>+ cairo_rectangle(cr, adjustedDestRect.x(), adjustedDestRect.y(), adjustedDestRect.width(), adjustedDestRect.height());
</ins><span class="cx"> cairo_fill(cr);
</span><span class="cx">
</span><span class="cx"> cairo_restore(cr);
</span></span></pre>
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