Using the device scale factor for glyph positioning

The master bug is http://code.google.com/p/chromium/issues/detail?id=138101 .
The corresponding WebKit changes for this CL are here:
https://bugs.webkit.org/show_bug.cgi?id=96137

BUG=

Review URL: https://codereview.appspot.com/6506099

git-svn-id: http://skia.googlecode.com/svn/trunk@5508 2bbb7eff-a529-9590-31e7-b0007b416f81

5 files changed, 66 insertions, 0 deletions

diff --git a/gyp/common_conditions.gypi b/gyp/common_conditions.gypi
index 1256ef6760..2a03c00607 100644
--- a/gyp/common_conditions.gypi
+++ b/gyp/common_conditions.gypi
@@ -3,6 +3,7 @@
 {
   'defines': [
     'SK_ALLOW_STATIC_GLOBAL_INITIALIZERS=<(skia_static_initializers)',
+    'SK_SUPPORT_HINTING_SCALE_FACTOR',
   ],
   'conditions' : [
     ['skia_gpu == 1',
diff --git a/include/core/SkPaint.h b/include/core/SkPaint.h
index 50fcdd825e..16b1b84c90 100644
--- a/include/core/SkPaint.h
+++ b/include/core/SkPaint.h
@@ -668,6 +668,20 @@ public:
     */
     void setTextSkewX(SkScalar skewX);
 
+#ifdef SK_SUPPORT_HINTING_SCALE_FACTOR
+    /** Return the paint's scale factor used for correctly rendering
+        glyphs in high DPI mode without text subpixel positioning.
+        @return the scale factor used for rendering glyphs in high DPI mode.
+    */
+    SkScalar getHintingScaleFactor() const { return fHintingScaleFactor; }
+
+    /** Set the paint's scale factor used for correctly rendering
+        glyphs in high DPI mode without text subpixel positioning.
+        @param the scale factor used for rendering glyphs in high DPI mode.
+    */
+    void setHintingScaleFactor(SkScalar hintingScaleFactor);
+#endif
+
     /** Describes how to interpret the text parameters that are passed to paint
         methods like measureText() and getTextWidths().
     */
@@ -910,6 +924,9 @@ private:
     SkScalar        fTextSize;
     SkScalar        fTextScaleX;
     SkScalar        fTextSkewX;
+#ifdef SK_SUPPORT_HINTING_SCALE_FACTOR
+    SkScalar        fHintingScaleFactor;
+#endif
 
     SkPathEffect*   fPathEffect;
     SkShader*       fShader;
diff --git a/src/core/SkPaint.cpp b/src/core/SkPaint.cpp
index 7e0ea97cdc..506db0e9c3 100644
--- a/src/core/SkPaint.cpp
+++ b/src/core/SkPaint.cpp
@@ -64,6 +64,9 @@ SkPaint::SkPaint() {
 
     fTextSize   = SkPaintDefaults_TextSize;
     fTextScaleX = SK_Scalar1;
+#ifdef SK_SUPPORT_HINTING_SCALE_FACTOR
+    fHintingScaleFactor = SK_Scalar1;
+#endif
     fColor      = SK_ColorBLACK;
     fMiterLimit = SkPaintDefaults_MiterLimit;
     fFlags      = SkPaintDefaults_Flags;
@@ -343,6 +346,13 @@ void SkPaint::setTextSkewX(SkScalar skewX) {
     fTextSkewX = skewX;
 }
 
+#ifdef SK_SUPPORT_HINTING_SCALE_FACTOR
+void SkPaint::setHintingScaleFactor(SkScalar hintingScaleFactor) {
+    GEN_ID_INC_EVAL(hintingScaleFactor != fHintingScaleFactor);
+    fHintingScaleFactor = hintingScaleFactor;
+}
+#endif
+
 void SkPaint::setTextEncoding(TextEncoding encoding) {
     if ((unsigned)encoding <= kGlyphID_TextEncoding) {
         GEN_ID_INC_EVAL((unsigned)encoding != fTextEncoding);
@@ -1500,6 +1510,9 @@ void SkScalerContext::MakeRec(const SkPaint& paint,
     rec->fTextSize = paint.getTextSize();
     rec->fPreScaleX = paint.getTextScaleX();
     rec->fPreSkewX  = paint.getTextSkewX();
+#ifdef SK_SUPPORT_HINTING_SCALE_FACTOR
+    rec->fHintingScaleFactor = paint.getHintingScaleFactor();
+#endif
 
     if (deviceMatrix) {
         rec->fPost2x2[0][0] = sk_relax(deviceMatrix->getScaleX());
@@ -1948,10 +1961,18 @@ enum FlatFlags {
 };
 
 // The size of a flat paint's POD fields
+
+#ifdef SK_SUPPORT_HINTING_SCALE_FACTOR
+static const uint32_t kPODPaintSize =   6 * sizeof(SkScalar) +
+                                        1 * sizeof(SkColor) +
+                                        1 * sizeof(uint16_t) +
+                                        6 * sizeof(uint8_t);
+#else
 static const uint32_t kPODPaintSize =   5 * sizeof(SkScalar) +
                                         1 * sizeof(SkColor) +
                                         1 * sizeof(uint16_t) +
                                         6 * sizeof(uint8_t);
+#endif
 
 /*  To save space/time, we analyze the paint, and write a truncated version of
     it if there are not tricky elements like shaders, etc.
@@ -1981,6 +2002,9 @@ void SkPaint::flatten(SkFlattenableWriteBuffer& buffer) const {
         ptr = write_scalar(ptr, this->getTextSize());
         ptr = write_scalar(ptr, this->getTextScaleX());
         ptr = write_scalar(ptr, this->getTextSkewX());
+#ifdef SK_SUPPORT_HINTING_SCALE_FACTOR
+        ptr = write_scalar(ptr, this->getHintingScaleFactor());
+#endif
         ptr = write_scalar(ptr, this->getStrokeWidth());
         ptr = write_scalar(ptr, this->getStrokeMiter());
         *ptr++ = this->getColor();
@@ -1997,6 +2021,9 @@ void SkPaint::flatten(SkFlattenableWriteBuffer& buffer) const {
         buffer.writeScalar(fTextSize);
         buffer.writeScalar(fTextScaleX);
         buffer.writeScalar(fTextSkewX);
+#ifdef SK_SUPPORT_HINTING_SCALE_FACTOR
+        buffer.writeScalar(fHintingScaleFactor);
+#endif
         buffer.writeScalar(fWidth);
         buffer.writeScalar(fMiterLimit);
         buffer.writeColor(fColor);
@@ -2042,6 +2069,9 @@ void SkPaint::unflatten(SkFlattenableReadBuffer& buffer) {
         this->setTextSize(read_scalar(pod));
         this->setTextScaleX(read_scalar(pod));
         this->setTextSkewX(read_scalar(pod));
+#ifdef SK_SUPPORT_HINTING_SCALE_FACTOR
+        this->setHintingScaleFactor(read_scalar(pod));
+#endif
         this->setStrokeWidth(read_scalar(pod));
         this->setStrokeMiter(read_scalar(pod));
         this->setColor(*pod++);
@@ -2068,6 +2098,9 @@ void SkPaint::unflatten(SkFlattenableReadBuffer& buffer) {
         this->setTextSize(buffer.readScalar());
         this->setTextScaleX(buffer.readScalar());
         this->setTextSkewX(buffer.readScalar());
+#ifdef SK_SUPPORT_HINTING_SCALE_FACTOR
+        this->setHintingScaleFactor(buffer.readScalar());
+#endif
         this->setStrokeWidth(buffer.readScalar());
         this->setStrokeMiter(buffer.readScalar());
         this->setColor(buffer.readColor());
diff --git a/src/core/SkScalerContext.h b/src/core/SkScalerContext.h
index 2443aafe6e..8175582522 100644
--- a/src/core/SkScalerContext.h
+++ b/src/core/SkScalerContext.h
@@ -34,6 +34,9 @@ struct SkScalerContextRec {
     SkScalar    fTextSize, fPreScaleX, fPreSkewX;
     SkScalar    fPost2x2[2][2];
     SkScalar    fFrameWidth, fMiterLimit;
+#ifdef SK_SUPPORT_HINTING_SCALE_FACTOR
+    SkScalar    fHintingScaleFactor;
+#endif
 
     //These describe the parameters to create (uniquely identify) the pre-blend.
     uint32_t    fLumBits;
diff --git a/src/ports/SkFontHost_FreeType.cpp b/src/ports/SkFontHost_FreeType.cpp
index f25223f750..ba0afd88a6 100644
--- a/src/ports/SkFontHost_FreeType.cpp
+++ b/src/ports/SkFontHost_FreeType.cpp
@@ -752,8 +752,20 @@ SkScalerContext_FreeType::SkScalerContext_FreeType(const SkDescriptor* desc)
         fMatrix22.xy = fMatrix22.yx = 0;
     }
 
+#ifdef SK_SUPPORT_HINTING_SCALE_FACTOR
+    SkScalar hintingScaleFactor = fRec.fHintingScaleFactor;
+
+    fScaleX = SkScalarToFixed(sx / hintingScaleFactor);
+    fScaleY = SkScalarToFixed(sy / hintingScaleFactor);
+
+    fMatrix22.xx *= hintingScaleFactor;
+    fMatrix22.xy *= hintingScaleFactor;
+    fMatrix22.yx *= hintingScaleFactor;
+    fMatrix22.yy *= hintingScaleFactor;
+#else
     fScaleX = SkScalarToFixed(sx);
     fScaleY = SkScalarToFixed(sy);
+#endif
 
     fLCDIsVert = SkToBool(fRec.fFlags & SkScalerContext::kLCD_Vertical_Flag);