[Linux] Enable subpixel text on high-dpi regardless of hinting

Expose deviceScaleFactor on GraphicsContext and use to selectively
enable subpixel text regardless of the system font hinting settings for
high-dpi systems.

BUG=373441
R=derat@chromium.org, tkent@chromium.org

Review URL: https://codereview.chromium.org/407553002

git-svn-id: svn://svn.chromium.org/blink/trunk@178485 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/rendering/RenderLayer.cpp

@@ -1809,7 +1809,7 @@ void RenderLayer::paintLayerContents(GraphicsContext* context, const LayerPainti
     bool shouldPaintContent = m_hasVisibleContent && isSelfPaintingLayer && !isPaintingOverlayScrollbars;
 
     float deviceScaleFactor = WebCore::deviceScaleFactor(renderer()->frame());
-    context->setUseHighResMarkers(deviceScaleFactor > 1.5f);
+    context->setDeviceScaleFactor(deviceScaleFactor);
 
     GraphicsContext* transparencyLayerContext = context;
 

third_party/WebKit/Source/platform/fonts/linux/FontPlatformDataLinux.cpp

@@ -35,6 +35,7 @@
 #include "platform/LayoutTestSupport.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/fonts/harfbuzz/FontPlatformDataHarfBuzz.h"
+#include "platform/graphics/GraphicsContext.h"
 #include "public/platform/linux/WebFontInfo.h"
 #include "public/platform/linux/WebFontRenderStyle.h"
 #include "public/platform/linux/WebSandboxSupport.h"
@@ -72,7 +73,8 @@ void FontPlatformData::setSubpixelRendering(bool useSubpixelRendering)
     useSkiaSubpixelRendering = useSubpixelRendering;
 }
 
-void FontPlatformData::setupPaint(SkPaint* paint, GraphicsContext*) const
+void FontPlatformData::setupPaint(SkPaint* paint, GraphicsContext* context)
+    const
 {
     paint->setAntiAlias(m_style.useAntiAlias);
     paint->setHinting(static_cast<SkPaint::Hinting>(m_style.hintStyle));
@@ -81,10 +83,13 @@ void FontPlatformData::setupPaint(SkPaint* paint, GraphicsContext*) const
     if (m_style.useAntiAlias)
         paint->setLCDRenderText(m_style.useSubpixelRendering);
 
+    // Do not enable subpixel text on low-dpi if full hinting is requested.
+    bool useSubpixelText = RuntimeEnabledFeatures::subpixelFontScalingEnabled()
+        && context && (paint->getHinting() != SkPaint::kFull_Hinting
+            || context->deviceScaleFactor() > 1.0f);
+
     // TestRunner specifically toggles the subpixel positioning flag.
-    if (RuntimeEnabledFeatures::subpixelFontScalingEnabled()
-        && paint->getHinting() != SkPaint::kFull_Hinting
-        && !LayoutTestSupport::isRunningLayoutTest())
+    if (useSubpixelText && !LayoutTestSupport::isRunningLayoutTest())
         paint->setSubpixelText(true);
     else
         paint->setSubpixelText(m_style.useSubpixelPositioning);

third_party/WebKit/Source/platform/graphics/GraphicsContext.cpp

@@ -123,9 +123,9 @@ GraphicsContext::GraphicsContext(SkCanvas* canvas, DisabledMode disableContextOr
     , m_disableDestructionChecks(false)
 #endif
     , m_disabledState(disableContextOrPainting)
+    , m_deviceScaleFactor(1.0f)
     , m_trackOpaqueRegion(false)
     , m_trackTextRegion(false)
-    , m_useHighResMarker(false)
     , m_updatingControlTints(false)
     , m_accelerated(false)
     , m_isCertainlyOpaque(true)
@@ -725,7 +725,8 @@ void GraphicsContext::drawLineForDocumentMarker(const FloatPoint& pt, float widt
     if (contextDisabled())
         return;
 
-    int deviceScaleFactor = m_useHighResMarker ? 2 : 1;
+    // Use 2x resources for a device scale factor of 1.5 or above.
+    int deviceScaleFactor = m_deviceScaleFactor > 1.5f ? 2 : 1;
 
     // Create the pattern we'll use to draw the underline.
     int index = style == DocumentMarkerGrammarLineStyle ? 1 : 0;

third_party/WebKit/Source/platform/graphics/GraphicsContext.h

@@ -197,9 +197,10 @@ public:
     CompositeOperator compositeOperation() const { return immutableState()->compositeOperator(); }
     blink::WebBlendMode blendModeOperation() const { return immutableState()->blendMode(); }
 
-    // Change the way document markers are rendered.
-    // Any deviceScaleFactor higher than 1.5 is enough to justify setting this flag.
-    void setUseHighResMarkers(bool isHighRes) { m_useHighResMarker = isHighRes; }
+    // Speicy the device scale factor which may change the way document markers
+    // and fonts are rendered.
+    void setDeviceScaleFactor(float factor) { m_deviceScaleFactor = factor; }
+    float deviceScaleFactor() const { return m_deviceScaleFactor; }
 
     // If true we are (most likely) rendering to a web page and the
     // canvas has been prepared with an opaque background. If false,
@@ -513,12 +514,12 @@ private:
 
     unsigned m_disabledState;
 
+    float m_deviceScaleFactor;
+
     // Activation for the above region tracking features
     bool m_trackOpaqueRegion : 1;
     bool m_trackTextRegion : 1;
 
-    // Are we on a high DPI display? If so, spelling and grammar markers are larger.
-    bool m_useHighResMarker : 1;
     // FIXME: Make this go away: crbug.com/236892
     bool m_updatingControlTints : 1;
     bool m_accelerated : 1;

third_party/WebKit/Source/web/PageWidgetDelegate.cpp

@@ -90,7 +90,7 @@ void PageWidgetDelegate::paint(Page* page, PageOverlayList* overlays, WebCanvas*
     GraphicsContext gc(canvas);
     gc.setCertainlyOpaque(background == Opaque);
     gc.applyDeviceScaleFactor(page->deviceScaleFactor());
-    gc.setUseHighResMarkers(page->deviceScaleFactor() > 1.5f);
+    gc.setDeviceScaleFactor(page->deviceScaleFactor());
     IntRect dirtyRect(rect);
     gc.save(); // Needed to save the canvas, not the GraphicsContext.
     FrameView* view = mainFrameView(page);