Track the region where text is painted.

Source/core/platform/graphics/skia/PlatformContextSkia.h

Index: Source/core/platform/graphics/skia/PlatformContextSkia.h
diff --git a/Source/core/platform/graphics/skia/PlatformContextSkia.h b/Source/core/platform/graphics/skia/PlatformContextSkia.h
index d33b9583b73424a979e92da367407b8c5eadbd34..1ccfe1142e167facff4503d5c0b69e63353b1ce5 100644
--- a/Source/core/platform/graphics/skia/PlatformContextSkia.h
+++ b/Source/core/platform/graphics/skia/PlatformContextSkia.h
@@ -186,6 +186,10 @@ public:
     // This will be an empty region unless tracking is enabled.
     const OpaqueRegionSkia& opaqueRegion() const { return m_opaqueRegion; }
 
+    void setTrackTextRegion(bool track) { m_trackTextRegion = track; }
+    // This will be an empty region unless tracking is enabled.
+    const SkRect& textRegion() const { return m_textRegion; }
+
     // After drawing directly to the context's canvas, use this function to notify the context so
     // it can track the opaque region.
     // FIXME: this is still needed only because ImageSkia::paintSkBitmap() may need to notify for a
@@ -238,10 +242,10 @@ public:
     void drawRect(const SkRect&, const SkPaint&);
     void drawIRect(const SkIRect&, const SkPaint&);
     void drawRRect(const SkRRect&, const SkPaint&);
-    void drawPosText(const void* text, size_t byteLength, const SkPoint pos[], const SkPaint&);
+    void drawPosText(const void* text, size_t byteLength, const SkPoint pos[], const SkRect& textRect, const SkPaint&);
     void drawPosTextH(const void* text, size_t byteLength, const SkScalar xpos[], SkScalar constY,
-        const SkPaint&);
-    void drawTextOnPath(const void* text, size_t byteLength, const SkPath&,
+        const SkRect& textRect, const SkPaint&);
+    void drawTextOnPath(const void* text, size_t byteLength, const SkPath&, const SkRect& textRect,
         const SkMatrix*, const SkPaint&);
 
 private:
@@ -255,6 +259,8 @@ private:
 
     void realizeSave(SkCanvas::SaveFlags);
 
+    void trackTextRegion(const SkRect& textRect);
+
     // Defines drawing style.
     struct State;
 
@@ -282,6 +288,10 @@ private:
     OpaqueRegionSkia m_opaqueRegion;
     bool m_trackOpaqueRegion;
 
+    // Tracks the region where text is painted via GraphicsContext.
+    bool m_trackTextRegion;
+    SkRect m_textRegion;
+
     bool m_printing;
     bool m_accelerated;
     bool m_drawingToImageBuffer;
@@ -476,30 +486,44 @@ inline void PlatformContextSkia::drawRRect(const SkRRect& rect, const SkPaint& p
         m_opaqueRegion.didDrawBounded(this, rect.getBounds(), paint);
 }
 
-inline void PlatformContextSkia::drawPosText(const void* text, size_t byteLength,
-    const SkPoint pos[], const SkPaint& paint)
+inline void PlatformContextSkia::drawPosText(const void* text,
+                                             size_t byteLength,
+                                             const SkPoint pos[],
+                                             const SkRect& textRect,
+                                             const SkPaint& paint)
 {
     m_canvas->drawPosText(text, byteLength, pos, paint);
+    trackTextRegion(textRect);

[eseidel, 2013/04/18 21:04:38]

Do we ever stop tracking?  Should this be didDrawTextInRect? or similar?

[alokp, 2013/04/18 22:22:37]

I like didDrawTextInRect. Changed.

 
     // FIXME: compute bounds for positioned text.
     if (m_trackOpaqueRegion)
         m_opaqueRegion.didDrawUnbounded(this, paint, OpaqueRegionSkia::FillOrStroke);
 }
 
-inline void PlatformContextSkia::drawPosTextH(const void* text, size_t byteLength,
-    const SkScalar xpos[], SkScalar constY, const SkPaint& paint)
+inline void PlatformContextSkia::drawPosTextH(const void* text,
+                                              size_t byteLength,
+                                              const SkScalar xpos[],
+                                              SkScalar constY,
+                                              const SkRect& textRect,
+                                              const SkPaint& paint)
 {
     m_canvas->drawPosTextH(text, byteLength, xpos, constY, paint);
+    trackTextRegion(textRect);
 
     // FIXME: compute bounds for positioned text.
     if (m_trackOpaqueRegion)
         m_opaqueRegion.didDrawUnbounded(this, paint, OpaqueRegionSkia::FillOrStroke);
 }
 
-inline void PlatformContextSkia::drawTextOnPath(const void* text, size_t byteLength,
-    const SkPath& path, const SkMatrix* matrix, const SkPaint& paint)
+inline void PlatformContextSkia::drawTextOnPath(const void* text,
+                                                size_t byteLength,
+                                                const SkPath& path,
+                                                const SkRect& textRect,
+                                                const SkMatrix* matrix,
+                                                const SkPaint& paint)
 {
     m_canvas->drawTextOnPath(text, byteLength, path, matrix, paint);
+    trackTextRegion(textRect);

[eseidel, 2013/04/18 21:04:38]

It's not clear to me that "textRect" is the right name.  If I pass the wrong
rect, what will happen?  Should this be textClipRect?  Will the rect actually
clip?

This introduces a whole new class of bugs (rect mismatches) to our text system,
but I suspect that the perf wins are definitely worth the added complexity.

[alokp, 2013/04/18 22:22:37]

It does not clip right now. The plan is to use for quick-reject and tracking
text-region for LCD text.
Yes. That is a concern. But I guess those bugs will be quite obvious - the text
will be rejected. Moreover in most cases we are reusing the text-rect computed
during layout, so mismatched rects may not be a big problem.

 
     // FIXME: compute bounds for positioned text.
     if (m_trackOpaqueRegion)