Changeset 49909 in webkit

Timestamp:

Oct 21, 2009 11:23:12 AM (15 years ago)

Author:

agl@chromium.org

Message:

2009-10-21 Adam Langley <​agl@google.com>

Reviewed by Eric Seidel.

Chromium Linux: disable subpixel text on layers.

​https://bugs.webkit.org/show_bug.cgi?id=30635
​http://code.google.com/p/chromium/issues/detail?id=25365

With the addition of layers for drawing rounded corners in r49641,
subpixel text on rounded rectangles broke. This is because the layer
only contains a single alpha channel and this is insufficient to
compose subpixel text correctly.

On Windows, a large body of code in TransparencyWin.cpp exists to try
to deal with this. Even then, in some cases, it downgrades to
anti-aliased text. We need a fix for the grevious effects quickly thus
this patch disables subpixel text when rendering into a layer.

This would be covered by existing tests except that subpixel text is
disabled for pixel tests on Chromium Linux.

• platform/graphics/chromium/FontLinux.cpp: (WebCore::isCanvasMultiLayered): (WebCore::adjustTextRenderMode): (WebCore::Font::drawGlyphs): (WebCore::Font::drawComplexText):

Location:

trunk/WebCore

Files:

• ChangeLog (modified) (1 diff)
• platform/graphics/chromium/FontLinux.cpp (modified) (6 diffs)

trunk/WebCore/ChangeLog

@@ +1 @@
+2009-10-21  Adam Langley  <agl@google.com>
+
+        Reviewed by Eric Seidel.
+
+        Chromium Linux: disable subpixel text on layers.
+
+        https://bugs.webkit.org/show_bug.cgi?id=30635
+        http://code.google.com/p/chromium/issues/detail?id=25365
+
+        With the addition of layers for drawing rounded corners in r49641,
+        subpixel text on rounded rectangles broke. This is because the layer
+        only contains a single alpha channel and this is insufficient to
+        compose subpixel text correctly.
+
+        On Windows, a large body of code in TransparencyWin.cpp exists to try
+        to deal with this. Even then, in some cases, it downgrades to
+        anti-aliased text. We need a fix for the grevious effects quickly thus
+        this patch disables subpixel text when rendering into a layer.
+
+        This would be covered by existing tests except that subpixel text is
+        disabled for pixel tests on Chromium Linux.
+
+        * platform/graphics/chromium/FontLinux.cpp:
+        (WebCore::isCanvasMultiLayered):
+        (WebCore::adjustTextRenderMode):
+        (WebCore::Font::drawGlyphs):
+        (WebCore::Font::drawComplexText):
+
 2009-10-21  Kevin Ollivier  <kevino@theolliviers.com>
 

trunk/WebCore/platform/graphics/chromium/FontLinux.cpp

@@ -58 +58 @@
 }
 
+static bool isCanvasMultiLayered(SkCanvas* canvas)
+{
+    SkCanvas::LayerIter layerIterator(canvas, false);
+    layerIterator.next();
+    return !layerIterator.done();
+}
+
+static bool adjustTextRenderMode(SkPaint* paint, bool isCanvasMultiLayered)
+{
+    // Our layers only have a single alpha channel. This means that subpixel
+    // rendered text cannot be compositied correctly when the layer is
+    // collapsed. Therefore, subpixel text is disabled when we are drawing
+    // onto a layer.
+    if (isCanvasMultiLayered)
+        paint->setLCDRenderText(false);
+}
+
 void Font::drawGlyphs(GraphicsContext* gc, const SimpleFontData* font,
                       const GlyphBuffer& glyphBuffer,  int from, int numGlyphs,
@@ -85 +102 @@
     SkCanvas* canvas = gc->platformContext()->canvas();
     int textMode = gc->platformContext()->getTextDrawingMode();
+    bool haveMultipleLayers = isCanvasMultiLayered(canvas);
 
     // We draw text up to two times (once for fill, once for stroke).
@@ -91 +109 @@
         gc->platformContext()->setupPaintForFilling(&paint);
         font->platformData().setupPaint(&paint);
+        adjustTextRenderMode(&paint, haveMultipleLayers);
         paint.setTextEncoding(SkPaint::kGlyphID_TextEncoding);
         paint.setColor(gc->fillColor().rgb());
@@ -103 +122 @@
         gc->platformContext()->setupPaintForStroking(&paint, 0, 0);
         font->platformData().setupPaint(&paint);
+        adjustTextRenderMode(&paint, haveMultipleLayers);
         paint.setTextEncoding(SkPaint::kGlyphID_TextEncoding);
         paint.setColor(gc->strokeColor().rgb());
@@ -473 +493 @@
 
     TextRunWalker walker(run, point.x(), this);
+    bool haveMultipleLayers = isCanvasMultiLayered(canvas);
 
     while (walker.nextScriptRun()) {
         if (fill) {
             walker.fontPlatformDataForScriptRun()->setupPaint(&fillPaint);
+            adjustTextRenderMode(&fillPaint, haveMultipleLayers);
             canvas->drawPosTextH(walker.glyphs(), walker.length() << 1, walker.xPositions(), point.y(), fillPaint);
         }
@@ -482 +504 @@
         if (stroke) {
             walker.fontPlatformDataForScriptRun()->setupPaint(&strokePaint);
+            adjustTextRenderMode(&strokePaint, haveMultipleLayers);
             canvas->drawPosTextH(walker.glyphs(), walker.length() << 1, walker.xPositions(), point.y(), strokePaint);
         }