SkRecordDraw: use SkCanvas::quickRejectY for text draws

src/record/SkRecordDraw.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkRecordDraw.h"
 
 namespace {
 
 // This is an SkRecord visitor that will draw that SkRecord to an SkCanvas.
 class Draw : SkNoncopyable {
 public:
     explicit Draw(SkCanvas* canvas) : fCanvas(canvas), fIndex(0), fClipEmpty(false) {}
 
     unsigned index() const { return fIndex; }
     void next() { ++fIndex; }
 
-    // No base case, so we'll be compile-time checked that we implemented all possibilities below.
-    template <typename T> void operator()(const T&);
+    template <typename T> void operator()(const T& r) {
+        if (!this->canSkip(r)) {
+            this->draw(r);
+            this->updateClip<T>();
+        }
+    }
 
 private:
-    // Must be called after any potential clip change.
-    void updateClip() { fClipEmpty = fCanvas->isClipEmpty(); }
+    // Can we skip this command right now?
+    template <typename T> bool canSkip(const T&) const {
+        // We can skip most commands if the clip is empty.  Exceptions are specialized below.
+        return fClipEmpty;
+    }
+
+    // No base case, so we'll be compile-time checked that we implemented all possibilities below.
+    template <typename T> void draw(const T&);
+
+    // Update fClipEmpty if necessary.
+    template <typename T> void updateClip() {
+        // Most commands don't change the clip.  Exceptions are specialized below.
+    }
 
     SkCanvas* fCanvas;
     unsigned fIndex;
     bool fClipEmpty;
 };
 
-template <> void Draw::operator()(const SkRecords::PushCull& r) {
-    if (r.popOffset != SkRecords::kUnsetPopOffset &&
-        fCanvas->quickReject(r.rect)) {
-        // We skip to the popCull, then the loop moves us just beyond it.
+// These commands may change the clip.
+#define UPDATE_CLIP(T) template <> void Draw::updateClip<SkRecords::T>() \
+    { fClipEmpty = fCanvas->isClipEmpty(); }
+UPDATE_CLIP(Restore);
+UPDATE_CLIP(SaveLayer);
+UPDATE_CLIP(ClipPath);
+UPDATE_CLIP(ClipRRect);
+UPDATE_CLIP(ClipRect);
+UPDATE_CLIP(ClipRegion);
+#undef UPDATE_CLIP
+
+// These commands must always run.
+#define CAN_SKIP(T) template <> bool Draw::canSkip(const SkRecords::T&) const { return false; }
+CAN_SKIP(Restore);
+CAN_SKIP(Save);
+CAN_SKIP(SaveLayer);
+CAN_SKIP(Clear);
+CAN_SKIP(PushCull);
+CAN_SKIP(PopCull);
+#undef CAN_SKIP
+
+// We can skip these commands only if they're intersecting an empty clip.

[tomhudson, 2014/04/14 17:12:16]

What does it mean for a clip to intersect the empty clip?

Or am I confusing an empty clip (no clip has been set, draw everything) with the
empty clip (clip everything away, draw nothing)? Is there a better name for
fClipEmpty?

[mtklein, 2014/04/14 18:08:16]

This is clip-everything-away-draw-nothing empty clip.  I think the older comment
was clearer.  Let me put that back.

+#define CAN_SKIP(T) template <> bool Draw::canSkip(const SkRecords::T& r) const \
+    { return fClipEmpty && SkRegion::kIntersect_Op == r.op; }
+CAN_SKIP(ClipPath);
+CAN_SKIP(ClipRRect);
+CAN_SKIP(ClipRect);
+CAN_SKIP(ClipRegion);
+#undef CAN_SKIP
+
+static bool can_skip_text(const SkCanvas& c, const SkPaint& p, SkScalar minY, SkScalar maxY) {
+    // If we're drawing vertical text, none of the checks we're about to do make any sense.
+    // We use canComputeFastBounds as a proxy for "is this text going to be rectangular?".
+    if (p.isVerticalText() || !p.canComputeFastBounds()) {
+        return false;
+    }
+
+    // Rather than checking the top and bottom font metrics, we guess.  Actually looking up the top
+    // and bottom metrics is slow, and this overapproximation should be good enough.
+    const SkScalar buffer = p.getTextSize() * 1.5f;
+    SkDEBUGCODE(SkPaint::FontMetrics metrics;)
+    SkDEBUGCODE(p.getFontMetrics(&metrics);)
+    SkASSERT(-buffer <= metrics.fTop);
+    SkASSERT(+buffer >= metrics.fBottom);
+    return c.quickRejectY(minY - buffer, maxY + buffer);
+}
+
+template <> bool Draw::canSkip(const SkRecords::DrawPosTextH& r) const {
+    return fClipEmpty || can_skip_text(*fCanvas, r.paint, r.y, r.y);
+}
+
+template <> bool Draw::canSkip(const SkRecords::DrawPosText& r) const {
+    if (fClipEmpty) {
+        return true;
+    }
+
+    // TODO(mtklein): may want to move this minY/maxY calculation into a one-time pass
+    const unsigned points = r.paint.countText(r.text, r.byteLength);
+    if (points == 0) {
+        return true;
+    }
+    SkScalar minY = SK_ScalarInfinity, maxY = SK_ScalarNegativeInfinity;
+    for (unsigned i = 0; i < points; i++) {
+        minY = SkTMin(minY, r.pos[i].fY);
+        maxY = SkTMax(maxY, r.pos[i].fY);
+    }
+
+    return can_skip_text(*fCanvas, r.paint, minY, maxY);
+}
+
+#define DRAW(T, call) template <> void Draw::draw(const SkRecords::T& r) { fCanvas->call; }
+DRAW(Restore, restore());
+DRAW(Save, save(r.flags));
+DRAW(SaveLayer, saveLayer(r.bounds, r.paint, r.flags));
+DRAW(PopCull, popCull());
+DRAW(Clear, clear(r.color));
+DRAW(Concat, concat(r.matrix));
+DRAW(SetMatrix, setMatrix(r.matrix));
+
+DRAW(ClipPath, clipPath(r.path, r.op, r.doAA));
+DRAW(ClipRRect, clipRRect(r.rrect, r.op, r.doAA));
+DRAW(ClipRect, clipRect(r.rect, r.op, r.doAA));
+DRAW(ClipRegion, clipRegion(r.region, r.op));
+
+DRAW(DrawBitmap, drawBitmap(r.bitmap, r.left, r.top, r.paint));
+DRAW(DrawBitmapMatrix, drawBitmapMatrix(r.bitmap, r.matrix, r.paint));
+DRAW(DrawBitmapNine, drawBitmapNine(r.bitmap, r.center, r.dst, r.paint));
+DRAW(DrawBitmapRectToRect, drawBitmapRectToRect(r.bitmap, r.src, r.dst, r.paint, r.flags));
+DRAW(DrawDRRect, drawDRRect(r.outer, r.inner, r.paint));
+DRAW(DrawOval, drawOval(r.oval, r.paint));
+DRAW(DrawPaint, drawPaint(r.paint));
+DRAW(DrawPath, drawPath(r.path, r.paint));
+DRAW(DrawPoints, drawPoints(r.mode, r.count, r.pts, r.paint));
+DRAW(DrawPosText, drawPosText(r.text, r.byteLength, r.pos, r.paint));
+DRAW(DrawPosTextH, drawPosTextH(r.text, r.byteLength, r.xpos, r.y, r.paint));
+DRAW(DrawRRect, drawRRect(r.rrect, r.paint));
+DRAW(DrawRect, drawRect(r.rect, r.paint));
+DRAW(DrawSprite, drawSprite(r.bitmap, r.left, r.top, r.paint));
+DRAW(DrawText, drawText(r.text, r.byteLength, r.x, r.y, r.paint));
+DRAW(DrawTextOnPath, drawTextOnPath(r.text, r.byteLength, r.path, r.matrix, r.paint));
+DRAW(DrawVertices, drawVertices(r.vmode, r.vertexCount, r.vertices, r.texs, r.colors,
+                                r.xmode.get(), r.indices, r.indexCount, r.paint));
+#undef DRAW
+
+// PushCull is a bit of a oddball.  We might be able to just skip until just past its popCull.
+template <> void Draw::draw(const SkRecords::PushCull& r) {
+    if (r.popOffset != SkRecords::kUnsetPopOffset && fCanvas->quickReject(r.rect)) {
         fIndex += r.popOffset;
     } else {
         fCanvas->pushCull(r.rect);
     }
 }
 
-// These commands might change the clip.
-#define CASE(T, call) \
-    template <> void Draw::operator()(const SkRecords::T& r) { fCanvas->call; this->updateClip(); }
-CASE(Restore, restore());
-CASE(SaveLayer, saveLayer(r.bounds, r.paint, r.flags));
-#undef CASE
-
-// These certainly do change the clip,
-// but we can skip them if they're intersecting with a clip that's already empty.
-#define CASE(T, call)  template <> void Draw::operator()(const SkRecords::T& r) {                \
-    if (!(fClipEmpty && SkRegion::kIntersect_Op == r.op)) { fCanvas->call; this->updateClip(); } \
-}
-CASE(ClipPath, clipPath(r.path, r.op, r.doAA));
-CASE(ClipRRect, clipRRect(r.rrect, r.op, r.doAA));
-CASE(ClipRect, clipRect(r.rect, r.op, r.doAA));
-CASE(ClipRegion, clipRegion(r.region, r.op));
-#undef CASE
-
-// Commands which must run regardless of the clip, but don't change it themselves.
-#define CASE(T, call) \
-    template <> void Draw::operator()(const SkRecords::T& r) { fCanvas->call; }
-CASE(Save, save(r.flags));
-CASE(Clear, clear(r.color));
-CASE(PopCull, popCull());
-#undef CASE
-
-// Nothing fancy below here.  These commands respect and don't change the clip.
-#define CASE(T, call) \
-    template <> void Draw::operator()(const SkRecords::T& r) { if (!fClipEmpty) fCanvas->call; }
-CASE(Concat, concat(r.matrix));
-CASE(SetMatrix, setMatrix(r.matrix));
-
-CASE(DrawBitmap, drawBitmap(r.bitmap, r.left, r.top, r.paint));
-CASE(DrawBitmapMatrix, drawBitmapMatrix(r.bitmap, r.matrix, r.paint));
-CASE(DrawBitmapNine, drawBitmapNine(r.bitmap, r.center, r.dst, r.paint));
-CASE(DrawBitmapRectToRect, drawBitmapRectToRect(r.bitmap, r.src, r.dst, r.paint, r.flags));
-CASE(DrawDRRect, drawDRRect(r.outer, r.inner, r.paint));
-CASE(DrawOval, drawOval(r.oval, r.paint));
-CASE(DrawPaint, drawPaint(r.paint));
-CASE(DrawPath, drawPath(r.path, r.paint));
-CASE(DrawPoints, drawPoints(r.mode, r.count, r.pts, r.paint));
-CASE(DrawPosText, drawPosText(r.text, r.byteLength, r.pos, r.paint));
-CASE(DrawPosTextH, drawPosTextH(r.text, r.byteLength, r.xpos, r.y, r.paint));
-CASE(DrawRRect, drawRRect(r.rrect, r.paint));
-CASE(DrawRect, drawRect(r.rect, r.paint));
-CASE(DrawSprite, drawSprite(r.bitmap, r.left, r.top, r.paint));
-CASE(DrawText, drawText(r.text, r.byteLength, r.x, r.y, r.paint));
-CASE(DrawTextOnPath, drawTextOnPath(r.text, r.byteLength, r.path, r.matrix, r.paint));
-CASE(DrawVertices, drawVertices(r.vmode, r.vertexCount, r.vertices, r.texs, r.colors,
-                                r.xmode.get(), r.indices, r.indexCount, r.paint));
-#undef CASE
-
 }  // namespace
 
 void SkRecordDraw(const SkRecord& record, SkCanvas* canvas) {
     for (Draw draw(canvas); draw.index() < record.count(); draw.next()) {
         record.visit(draw.index(), draw);
     }
 }