Use BBH reserve hook to preallocate space for tiles.

src/core/SkTileGrid.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkTileGrid.h"
 
 SkTileGrid::SkTileGrid(int xTiles, int yTiles, const SkTileGridFactory::TileGridInfo& info)
     : fXTiles(xTiles)
     , fYTiles(yTiles)
     , fInvWidth( SkScalarInvert(info.fTileInterval.width()))
     , fInvHeight(SkScalarInvert(info.fTileInterval.height()))
     , fMarginWidth (info.fMargin.fWidth +1)  // Margin is offset by 1 as a provision for AA and
     , fMarginHeight(info.fMargin.fHeight+1)  // to cancel the outset applied by getClipDeviceBounds.
     , fOffset(SkPoint::Make(info.fOffset.fX, info.fOffset.fY))
     , fGridBounds(SkRect::MakeWH(xTiles * info.fTileInterval.width(),
                                  yTiles * info.fTileInterval.height()))
     , fTiles(SkNEW_ARRAY(SkTDArray<unsigned>, xTiles * yTiles)) {}
 
 SkTileGrid::~SkTileGrid() {
     SkDELETE_ARRAY(fTiles);
 }
 
+void SkTileGrid::reserve(unsigned opCount) {
+    if (fXTiles * fYTiles == 0) {
+        return;  // A tileless tile grid is nonsensical, but happens in at least cc_unittests.
+    }
+
+    // If we assume every op we're about to try to insert() falls within our grid bounds,
+    // then every op has to hit at least one tile.  In fact, a quick scan over our small
+    // SKP set shows that in the average SKP, each op hits two 256x256 tiles.
+
+    // If we take those observations and further assume the ops are distributed evenly
+    // across the picture, we get this guess for number of ops per tile:
+    const int opsPerTileGuess = (2 * opCount) / (fXTiles * fYTiles);
+
+    for (SkTDArray<unsigned>* tile = fTiles; tile != fTiles + (fXTiles * fYTiles); tile++) {
+        tile->setReserve(opsPerTileGuess);
+    }
+
+    // In practice, this heuristic means we'll temporarily allocate about 30% more bytes
+    // than if we made no setReserve() calls, but time spent in insert() drops by about 50%.
+}
+
+void SkTileGrid::flushDeferredInserts() {
+    for (SkTDArray<unsigned>* tile = fTiles; tile != fTiles + (fXTiles * fYTiles); tile++) {
+        tile->shrinkToFit();
+    }
+}
+
 // Adjustments to user-provided bounds common to both insert() and search().
 // Call this after making insert- or search- specific adjustments.
 void SkTileGrid::commonAdjust(SkRect* rect) const {
     // Apply our offset.
     rect->offset(fOffset);
 
     // Scrunch the bounds in just a little to make the right and bottom edges
     // exclusive.  We want bounds of exactly one tile to hit exactly one tile.
     rect->fRight  -= SK_ScalarNearlyZero;
     rect->fBottom -= SK_ScalarNearlyZero;
@@ skipping 95 matching lines @@
         // We did find an earliest op. Output it, and step forward every tile that contains it.
         results->push(earliest);
         for (int i = 0; i < starts.count(); i++) {
             if (starts[i] < ends[i] && *starts[i] == earliest) {
                 starts[i]++;
             }
         }
     }
 }