Attachment 301043 Details for Bug 154283 – Patch

[patch] Patch

bug-154283-20170209174913.patch (text/plain), 4.00 KB, created by Miguel Gomez on 2017-02-09 08:51:39 PST

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Creator: Miguel Gomez

Created: 2017-02-09 08:51:39 PST

Size: 4.00 KB

patch

obsolete

>Subversion Revision: 211857
>diff --git a/Source/WebCore/ChangeLog b/Source/WebCore/ChangeLog
>index 885e351c25764d7cab5b2e8a476e75be9a19c18d..0daae39cc972fc068df2e5317f482aeccfd5bf33 100644
>--- a/Source/WebCore/ChangeLog
>+++ b/Source/WebCore/ChangeLog
>@@ -1,3 +1,26 @@
>+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 NOBODY (OOPS!).
>+
>+        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.
>+
>+        No new tests.
>+
>+        * platform/graphics/cairo/CairoUtilities.cpp:
>+        (WebCore::drawPatternToCairoContext):
>+
> 2017-02-08  Zan Dobersek  <zdobersek@igalia.com>
> 
>         [EME] Implement MediaKeySession::remove()
>diff --git a/Source/WebCore/platform/graphics/cairo/CairoUtilities.cpp b/Source/WebCore/platform/graphics/cairo/CairoUtilities.cpp
>index fc485894014f2d2d0baa2893989b13934ba2a7d6..440c6c6cb0044a9002b2f337e7f307f4e5cf497e 100644
>--- a/Source/WebCore/platform/graphics/cairo/CairoUtilities.cpp
>+++ b/Source/WebCore/platform/graphics/cairo/CairoUtilities.cpp
>@@ -205,8 +205,28 @@ void drawPatternToCairoContext(cairo_t* cr, cairo_surface_t* image, const IntSiz
>     cairo_pattern_t* pattern = cairo_pattern_create_for_surface(image);
>     cairo_pattern_set_extend(pattern, CAIRO_EXTEND_REPEAT);
> 
>+    // 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.
>     cairo_matrix_t patternMatrix = cairo_matrix_t(patternTransform);
>-    cairo_matrix_t phaseMatrix = {1, 0, 0, 1, phase.x() + tileRect.x() * patternTransform.a(), phase.y() + tileRect.y() * patternTransform.d()};
>+    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()};
>     cairo_matrix_t combined;
>     cairo_matrix_multiply(&combined, &patternMatrix, &phaseMatrix);
>     cairo_matrix_invert(&combined);
>@@ -215,7 +235,7 @@ void drawPatternToCairoContext(cairo_t* cr, cairo_surface_t* image, const IntSiz
>     cairo_set_operator(cr, op);
>     cairo_set_source(cr, pattern);
>     cairo_pattern_destroy(pattern);
>-    cairo_rectangle(cr, destRect.x(), destRect.y(), destRect.width(), destRect.height());
>+    cairo_rectangle(cr, adjustedDestRect.x(), adjustedDestRect.y(), adjustedDestRect.width(), adjustedDestRect.height());
>     cairo_fill(cr);
> 
>     cairo_restore(cr);

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