cc: Consolidate the analysis_canvas operations

skia/ext/analysis_canvas.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/debug/trace_event.h"
 #include "skia/ext/analysis_canvas.h"
 #include "third_party/skia/include/core/SkDevice.h"
 #include "third_party/skia/include/core/SkDraw.h"
 #include "third_party/skia/include/core/SkRRect.h"
+#include "third_party/skia/src/core/SkRasterClip.h"
 #include "ui/gfx/rect_conversions.h"
 
 namespace {
 
 // FIXME: Arbitrary number. Requires tuning & experimentation.
 // Probably requires per-platform tuning; N10 average draw call takes
 // 25x as long as Z620.
 const int gPictureCostThreshold = 1000;
 
+static bool isSolidColorPaint(const SkPaint& paint) {

[Justin Novosad, 2013/03/05 22:14:02]

I think isPaintOpaque (SkPaintPriv.cpp in skia) could inspire you to handle more
cases.  Look how it handles xfer modes.

+  SkXfermode::Mode xferMode;
+
+  // getXfermode can return a NULL, but that is handled
+  // gracefully by AsMode (NULL turns into kSrcOver mode).
+  SkXfermode::AsMode(paint.getXfermode(), &xferMode);
+
+  // Paint is solid color if the following holds:
+  // - Alpha is 1.0, style is fill, and there are no special effects
+  // - Xfer mode is either kSrc or kSrcOver (kSrcOver is equivalent
+  //   to kSrc if source alpha is 1.0, which is already checked).
+  return (paint.getAlpha() == 255 &&
+          !paint.getShader() &&
+          !paint.getLooper() &&
+          !paint.getMaskFilter() &&
+          !paint.getColorFilter() &&
+          paint.getStyle() == SkPaint::kFill_Style &&
+          (xferMode == SkXfermode::kSrc_Mode ||
+           xferMode == SkXfermode::kSrcOver_Mode));
 }
 
+static bool isFullQuad(const SkDraw& draw,
+                       const SkRect& canvasRect,
+                       const SkRect& drawnRect) {
+  SkRect drawBitmapRect;
+  draw.fBitmap->getBounds(&drawBitmapRect);
+  SkRect clipRect = SkRect::Make(draw.fRC->getBounds());
+  SkRect deviceRect;
+  draw.fMatrix->mapRect(&deviceRect, drawnRect);

[Justin Novosad, 2013/03/05 22:14:02]

The way this is implemented, you will sometimes get false positives. To be
conservative you should return false if draw.fMAtrix->rectStaysRect() returns
false.  If the matrix applies a rotation or perspective transform, mapRect will
give an axis-aligned rectangle that contains the transformed rect.  Right now,
there is no method to compute an axis-aligned rect that is contained by the
transformed rect, which is what you would need in order to be safe.

+
+  // The drawn rect covers the full canvas, if the following conditions hold:
+  // - Clip rect is an actual rectangle.
+  // - The rect we're drawing (post-transform) contains the clip rect.
+  //   That is, all of clip rect will be colored by the rect.
+  // - Clip rect contains the canvas rect.
+  //   That is, we're not clipping to a portion of this canvas.
+  // - The bitmap into which the draw call happens is at least as
+  //   big as the canvas rect
+  return draw.fRC->isRect() &&

[Justin Novosad, 2013/03/05 22:14:02]

This is not safe.  AnalysisCanvas converts clipPath calls to clipRect calls,
using the path bounds.  This approach is conservative for testing for
intersections, but it is unsafe for 'contains' tests.  The purpose of this hack
is to prevent SkRasterClip from rasterizing paths, which would be a huge
computational burden. I have a skia CL on the back burner that refactors this
optimization in a way that would solve your problem:
https://codereview.appspot.com/7301054/  Once this patch lands, you will be able
to call the contains method on the canvas's SkClipStack, which will provide the
added benefit of being able to test against certain types of path clips (ovals,
rounded rects, etc.)  Until then, I am not sure how you should handle the
clipPath case here. Perhaps AnalysisCanvas could maintain a stack of counters of
clipPath calls.  Something like: on save, you would push stack.last; on restore,
you would pop; on clipPath, you would increment stack.last

+         deviceRect.contains(clipRect) &&
+         clipRect.contains(canvasRect) &&
+         drawBitmapRect.contains(canvasRect);
+}
+
+} // namespace
+
 namespace skia {
 
 AnalysisDevice::AnalysisDevice(const SkBitmap& bm)
   : INHERITED(bm)
-  , estimatedCost_(0) {
+  , estimatedCost_(0)
+  , isForcedNotSolid_(false)
+  , isForcedNotTransparent_(false)
+  , isSolidColor_(false)
+  , isTransparent_(false) {
 
 }
 
 AnalysisDevice::~AnalysisDevice() {
 
 }
 
 int AnalysisDevice::getEstimatedCost() const {
   return estimatedCost_;
 }
 
+bool AnalysisDevice::getColorIfSolid(SkColor* color) const {
+  if (isSolidColor_)
+    *color = color_;
+  return isSolidColor_;
+}
+
+bool AnalysisDevice::isTransparent() const {
+  return isTransparent_;
+}
+
+void AnalysisDevice::setForceNotSolid(bool flag) {
+  isForcedNotSolid_ = flag;
+  if (isForcedNotSolid_)
+    isSolidColor_ = false;
+}
+
+void AnalysisDevice::setForceNotTransparent(bool flag) {
+  isForcedNotTransparent_ = flag;
+  if (isForcedNotTransparent_)
+    isTransparent_ = false;
+}
+
 void AnalysisDevice::clear(SkColor color) {
-    ++estimatedCost_;
+  ++estimatedCost_;
+
+  isTransparent_ = (!isForcedNotTransparent_ && SkColorGetA(color) == 0);
+
+  if (!isForcedNotSolid_ && SkColorGetA(color) == 255) {
+    isSolidColor_ = true;
+    color_ = color;
+  }
+  else {
+    isSolidColor_ = false;
+  }
 }
 
 void AnalysisDevice::drawPaint(const SkDraw&, const SkPaint& paint) {

[Justin Novosad, 2013/03/05 22:14:02]

This method could do more. it fills the entire clip, so it would be easy to
determine whether it covers the entire canvas.

   ++estimatedCost_;
+  isSolidColor_ = false;
+  isTransparent_ = false;
 }
 
 void AnalysisDevice::drawPoints(const SkDraw&, SkCanvas::PointMode mode,
                           size_t count, const SkPoint[],
                           const SkPaint& paint) {
   ++estimatedCost_;
+  isSolidColor_ = false;
+  isTransparent_ = false;
 }
 
-void AnalysisDevice::drawRect(const SkDraw&, const SkRect& r,
+void AnalysisDevice::drawRect(const SkDraw& draw, const SkRect& rect,
                         const SkPaint& paint) {
+
   // FIXME: if there's a pending image decode & resize, more expensive
   if (paint.getMaskFilter()) {
     estimatedCost_ += 300;
   }
   ++estimatedCost_;
+
+  bool doesCoverCanvas = isFullQuad(draw,
+                                    SkRect::MakeWH(width(), height()),
+                                    rect);
+
+  SkXfermode::Mode xferMode;
+  SkXfermode::AsMode(paint.getXfermode(), &xferMode);
+
+  // This canvas will become transparent if the following holds:
+  // - The quad is a full tile quad
+  // - We're not in "forced not transparent" mode
+  // - Transfer mode is clear (0 color, 0 alpha)
+  //
+  // If the paint alpha is not 0, or if the transfrer mode is
+  // not src, then this canvas will not be transparent.
+  //
+  // In all other cases, we keep the current transparent value
+  if (doesCoverCanvas &&
+      !isForcedNotTransparent_ &&
+      xferMode == SkXfermode::kClear_Mode) {
+    isTransparent_ = true;
+  }
+  else if (paint.getAlpha() != 0 ||
+           xferMode != SkXfermode::kSrc_Mode) {
+    isTransparent_ = false;
+  }
+
+  // This bitmap is solid if and only if the following holds.
+  // Note that this might be overly conservative:
+  // - We're not in "forced not solid" mode
+  // - Paint is solid color
+  // - The quad is a full tile quad
+  if (!isForcedNotSolid_ &&
+      isSolidColorPaint(paint) &&
+      doesCoverCanvas) {
+    isSolidColor_ = true;
+    color_ = paint.getColor();
+  }
+  else {
+    isSolidColor_ = false;
+  }
 }
 
 void AnalysisDevice::drawOval(const SkDraw&, const SkRect& oval,

[Justin Novosad, 2013/03/05 22:14:02]

FWIW: It is trivial to compute whether an oval contains the canvas rect.

                         const SkPaint& paint) {
   ++estimatedCost_;
+  isSolidColor_ = false;
+  isTransparent_ = false;
 }
 
 void AnalysisDevice::drawPath(const SkDraw&, const SkPath& path,
                         const SkPaint& paint,
                         const SkMatrix* prePathMatrix ,
                         bool pathIsMutable ) {
   // On Z620, every antialiased path costs us about 300us.
   // We've only seen this in practice on filled paths, but
   // we expect it to apply to all path stroking modes.
   if (paint.getMaskFilter()) {
     estimatedCost_ += 300;
   }
   ++estimatedCost_;
+  isSolidColor_ = false;
+  isTransparent_ = false;
 }
 
 void AnalysisDevice::drawBitmap(const SkDraw&, const SkBitmap& bitmap,
                           const SkIRect* srcRectOrNull,
-                          const SkMatrix& matrix, const SkPaint& paint)
-                          {
+                          const SkMatrix& matrix, const SkPaint& paint) {
   ++estimatedCost_;
+  isSolidColor_ = false;
+  isTransparent_ = false;
 }
 
 void AnalysisDevice::drawSprite(const SkDraw&, const SkBitmap& bitmap,
                           int x, int y, const SkPaint& paint) {
   ++estimatedCost_;
+  isSolidColor_ = false;
+  isTransparent_ = false;
 }
 
-void AnalysisDevice::drawBitmapRect(const SkDraw&, const SkBitmap&,
+void AnalysisDevice::drawBitmapRect(const SkDraw& draw, const SkBitmap&,
                               const SkRect* srcOrNull, const SkRect& dst,
                               const SkPaint& paint) {
   ++estimatedCost_;
+
+  // Call drawRect to determine transparency,
+  // but reset solid color to false.
+  drawRect(draw, dst, paint);
+  isSolidColor_ = false;
 }
 
 
 void AnalysisDevice::drawText(const SkDraw&, const void* text, size_t len,
-                        SkScalar x, SkScalar y, const SkPaint& paint)
-                        {
+                        SkScalar x, SkScalar y, const SkPaint& paint) {
   ++estimatedCost_;
+  isSolidColor_ = false;
+  isTransparent_ = false;
 }
 
 void AnalysisDevice::drawPosText(const SkDraw& draw, const void* text, size_t len,
                            const SkScalar pos[], SkScalar constY,
                            int scalarsPerPos, const SkPaint& paint) {
   // FIXME: On Z620, every glyph cache miss costs us about 10us.
   // We don't have a good mechanism for predicting glyph cache misses.
   ++estimatedCost_;
+  isSolidColor_ = false;
+  isTransparent_ = false;
 }
 
 void AnalysisDevice::drawTextOnPath(const SkDraw&, const void* text, size_t len,
                               const SkPath& path, const SkMatrix* matrix,
                               const SkPaint& paint) {
   ++estimatedCost_;
+  isSolidColor_ = false;
+  isTransparent_ = false;
 }
 
 #ifdef SK_BUILD_FOR_ANDROID
 void AnalysisDevice::drawPosTextOnPath(const SkDraw& draw, const void* text,
                                  size_t len,
                                  const SkPoint pos[], const SkPaint& paint,
-                                 const SkPath& path, const SkMatrix* matrix)
-                                 {
+                                 const SkPath& path, const SkMatrix* matrix) {
   ++estimatedCost_;
+  isSolidColor_ = false;
+  isTransparent_ = false;
 }
 #endif
 
 void AnalysisDevice::drawVertices(const SkDraw&, SkCanvas::VertexMode,
                             int vertexCount,
                             const SkPoint verts[], const SkPoint texs[],
                             const SkColor colors[], SkXfermode* xmode,
                             const uint16_t indices[], int indexCount,
                             const SkPaint& paint) {
   ++estimatedCost_;
+  isSolidColor_ = false;
+  isTransparent_ = false;
 }
 
 void AnalysisDevice::drawDevice(const SkDraw&, SkDevice*, int x, int y,
                           const SkPaint&) {
   ++estimatedCost_;
+  isSolidColor_ = false;
+  isTransparent_ = false;
 }
 
 
 
-
 AnalysisCanvas::AnalysisCanvas(AnalysisDevice* device)
-  : INHERITED(device) {
-
+  : INHERITED(device)
+  , savedLayerStackSize_(0) {
 }
 
 AnalysisCanvas::~AnalysisCanvas() {
 }
 
 
 bool AnalysisCanvas::isCheap() const {
   return getEstimatedCost() < gPictureCostThreshold;
 }
 
+bool AnalysisCanvas::getColorIfSolid(SkColor* color) const {
+  return (static_cast<AnalysisDevice*>(getDevice()))->getColorIfSolid(color);
+}
+
+bool AnalysisCanvas::isTransparent() const {
+  return (static_cast<AnalysisDevice*>(getDevice()))->isTransparent();
+}
+
 int AnalysisCanvas::getEstimatedCost() const {
   return (static_cast<AnalysisDevice*>(getDevice()))->getEstimatedCost();
 }
 
-
 bool AnalysisCanvas::clipRect(const SkRect& rect, SkRegion::Op op,
                         bool doAA) {
   return INHERITED::clipRect(rect, op, doAA);
 }
 
 bool AnalysisCanvas::clipPath(const SkPath& path, SkRegion::Op op,
                         bool doAA) {
   return INHERITED::clipRect(path.getBounds(), op, doAA);
 }
 
 bool AnalysisCanvas::clipRRect(const SkRRect& rrect, SkRegion::Op op,
                          bool doAA) {
   return INHERITED::clipRect(rrect.getBounds(), op, doAA);
 }
 
-int AnalysisCanvas::saveLayer(const SkRect* bounds, const SkPaint*, 
+int AnalysisCanvas::save(SkCanvas::SaveFlags flags) {
+  INHERITED::save(flags);
+}
+
+int AnalysisCanvas::saveLayer(const SkRect* bounds, const SkPaint* paint, 
                               SkCanvas::SaveFlags flags) {
+  // If after we draw to the saved layer, we have to blend with the current
+  // layer, then we can conservatively say that the canvas will not be of
+  // solid color.
+  if ((paint && !isSolidColorPaint(*paint)) ||
+      (bounds && !bounds->contains(
+          SkRect::MakeWH(getDevice()->width(), getDevice()->height()))))
+    (static_cast<AnalysisDevice*>(getDevice()))->setForceNotSolid(true);
+
+  // If after we draw to the save layer, we have to blend with the current
+  // layer using any part of the current layer's alpha, then we can
+  // conservatively say that the canvas will not be transparent.
+  SkXfermode::Mode xferMode = SkXfermode::kSrc_Mode;
+  if (paint)
+    SkXfermode::AsMode(paint->getXfermode(), &xferMode);
+  if (xferMode != SkXfermode::kSrc_Mode)
+    (static_cast<AnalysisDevice*>(getDevice()))->setForceNotTransparent(true);
+
+  ++savedLayerStackSize_;
+
   // Actually saving a layer here could cause a new bitmap to be created
   // and real rendering to occur.
-  int count = SkCanvas::save(flags);
+  int count = INHERITED::save(flags);
   if (bounds) {
     INHERITED::clipRectBounds(bounds, flags, NULL);
   }
   return count;
 }
 
+void AnalysisCanvas::restore() {
+  INHERITED::restore();
+
+  if (--savedLayerStackSize_ == 0) {

[Justin Novosad, 2013/03/05 22:14:02]

This is overly conservative.  You could store the index of the first stack level
that that called setForceNotSolid with true, and set it back to false when that
stack level is popped, rather than requiring all layers to be popped off.  Same
thing for setForceNotTransparent.

+    (static_cast<AnalysisDevice*>(getDevice()))->setForceNotSolid(false);
+    (static_cast<AnalysisDevice*>(getDevice()))->setForceNotTransparent(false);
+  }
+}
+
 }  // namespace skia