Changeset 132731 in webkit

Timestamp:

Oct 27, 2012, 10:18:12 AM (13 years ago)

Author:

leviw@chromium.org

Message:

Background images can incorrectly repeat with sub-pixel layout
​https://bugs.webkit.org/show_bug.cgi?id=94622

Reviewed by Emil A Eklund.

Source/WebCore:

Attempting to better match author expectations when painting tiled background images. When under
the effects of zoom with sub-pixel layout enabled, the drawn size of a rendered element can
differ depending on its location. This change looks at the size of the scaled tiled background
image size, and either ceils or floors that value depending on if tiling that value will
result in us being one pixel or less short of covering the background size. This is a heuristic,
as sub-pixel/zooming isn't specced.

Test: fast/sub-pixel/scaled-background-image.html

• rendering/RenderBoxModelObject.cpp:

(WebCore::applySubPixelHeuristicForTileSize):
(WebCore):
(WebCore::RenderBoxModelObject::calculateFillTileSize):

LayoutTests:

• fast/sub-pixel/scaled-background-image-expected.html: Added.
• fast/sub-pixel/scaled-background-image.html: Added.

Location:

trunk

Files:

• LayoutTests/ChangeLog (modified) (1 diff)
• LayoutTests/fast/sub-pixel/scaled-background-image-expected.html (added)
• LayoutTests/fast/sub-pixel/scaled-background-image.html (added)
• Source/WebCore/ChangeLog (modified) (1 diff)
• Source/WebCore/rendering/RenderBoxModelObject.cpp (modified) (3 diffs)

trunk/LayoutTests/ChangeLog

@@ +1 @@
+2012-10-27  Levi Weintraub  <leviw@chromium.org>
+
+        Background images can incorrectly repeat with sub-pixel layout
+        https://bugs.webkit.org/show_bug.cgi?id=94622
+
+        Reviewed by Emil A Eklund.
+
+        * fast/sub-pixel/scaled-background-image-expected.html: Added.
+        * fast/sub-pixel/scaled-background-image.html: Added.
+
 2012-10-26  Balazs Kelemen  <kbalazs@webkit.org>
 

trunk/Source/WebCore/ChangeLog

@@ +1 @@
+2012-10-27  Levi Weintraub  <leviw@chromium.org>
+
+        Background images can incorrectly repeat with sub-pixel layout
+        https://bugs.webkit.org/show_bug.cgi?id=94622
+
+        Reviewed by Emil A Eklund.
+
+        Attempting to better match author expectations when painting tiled background images. When under
+        the effects of zoom with sub-pixel layout enabled, the drawn size of a rendered element can
+        differ depending on its location. This change looks at the size of the scaled tiled background
+        image size, and either ceils or floors that value depending on if tiling that value will
+        result in us being one pixel or less short of covering the background size. This is a heuristic,
+        as sub-pixel/zooming isn't specced.
+
+        Test: fast/sub-pixel/scaled-background-image.html
+
+        * rendering/RenderBoxModelObject.cpp:
+        (WebCore::applySubPixelHeuristicForTileSize):
+        (WebCore):
+        (WebCore::RenderBoxModelObject::calculateFillTileSize):
+
 2012-10-27  Sheriff Bot  <webkit.review.bot@gmail.com>
 

trunk/Source/WebCore/rendering/RenderBoxModelObject.cpp

@@ -1047 +1047 @@
 }
 
+static inline void applySubPixelHeuristicForTileSize(LayoutSize& tileSize, const IntSize& positioningAreaSize)
+{
+    tileSize.setWidth(positioningAreaSize.width() - tileSize.width() <= 1 ? tileSize.width().ceil() : tileSize.width().floor());
+    tileSize.setHeight(positioningAreaSize.height() - tileSize.height() <= 1 ? tileSize.height().ceil() : tileSize.height().floor());
+}
+
 IntSize RenderBoxModelObject::calculateFillTileSize(const FillLayer* fillLayer, const IntSize& positioningAreaSize) const
 {
@@ -1057 +1063 @@
     switch (type) {
         case SizeLength: {
-            int w = positioningAreaSize.width();
-            int h = positioningAreaSize.height();
+            LayoutSize tileSize = positioningAreaSize;
 
             Length layerWidth = fillLayer->size().size.width();
@@ -1064 +1069 @@
 
             if (layerWidth.isFixed())
-                w = layerWidth.value();
+                tileSize.setWidth(layerWidth.value());
             else if (layerWidth.isPercent() || layerHeight.isViewportPercentage())
-                w = valueForLength(layerWidth, positioningAreaSize.width(), renderView);
+                tileSize.setWidth(valueForLength(layerWidth, positioningAreaSize.width(), renderView));
             
             if (layerHeight.isFixed())
-                h = layerHeight.value();
+                tileSize.setHeight(layerHeight.value());
             else if (layerHeight.isPercent() || layerHeight.isViewportPercentage())
-                h = valueForLength(layerHeight, positioningAreaSize.height(), renderView);
-            
+                tileSize.setHeight(valueForLength(layerHeight, positioningAreaSize.height(), renderView));
+
+            applySubPixelHeuristicForTileSize(tileSize, positioningAreaSize);
+
             // If one of the values is auto we have to use the appropriate
             // scale to maintain our aspect ratio.
             if (layerWidth.isAuto() && !layerHeight.isAuto()) {
                 if (imageIntrinsicSize.height())
-                    w = imageIntrinsicSize.width() * h / imageIntrinsicSize.height();        
+                    tileSize.setWidth(imageIntrinsicSize.width() * tileSize.height() / imageIntrinsicSize.height());
             } else if (!layerWidth.isAuto() && layerHeight.isAuto()) {
                 if (imageIntrinsicSize.width())
-                    h = imageIntrinsicSize.height() * w / imageIntrinsicSize.width();
+                    tileSize.setHeight(imageIntrinsicSize.height() * tileSize.width() / imageIntrinsicSize.width());
             } else if (layerWidth.isAuto() && layerHeight.isAuto()) {
                 // If both width and height are auto, use the image's intrinsic size.
-                w = imageIntrinsicSize.width();
-                h = imageIntrinsicSize.height();
+                tileSize = imageIntrinsicSize;
             }
             
-            return IntSize(max(0, w), max(0, h));
+            tileSize.clampNegativeToZero();
+            return flooredIntSize(tileSize);
         }
         case SizeNone: {