raster_cache.cc

// Copyright 2016 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 "flutter/flow/raster_cache.h"

#include <stdlib.h>

#include <vector>

#include "flutter/common/threads.h"
#include "flutter/glue/trace_event.h"
#include "lib/ftl/logging.h"
#include "third_party/skia/include/core/SkCanvas.h"
#include "third_party/skia/include/core/SkImage.h"
#include "third_party/skia/include/core/SkPicture.h"
#include "third_party/skia/include/core/SkSurface.h"

namespace flow {

static const int kRasterThreshold = 3;

static bool isWorthRasterizing(SkPicture* picture) {
  // TODO(abarth): We should find a better heuristic here that lets us avoid
  // wasting memory on trivial layers that are easy to re-rasterize every frame.
  return picture->approximateOpCount() > 10;
}

static sk_sp<SkShader> CreateCheckerboardShader(SkColor c1,
                                                SkColor c2,
                                                int size) {
  SkBitmap bm;
  bm.allocN32Pixels(2 * size, 2 * size);
  bm.eraseColor(c1);
  bm.eraseArea(SkIRect::MakeLTRB(0, 0, size, size), c2);
  bm.eraseArea(SkIRect::MakeLTRB(size, size, 2 * size, 2 * size), c2);
  return SkShader::MakeBitmapShader(bm, SkShader::kRepeat_TileMode,
                                    SkShader::kRepeat_TileMode);
}

static void DrawCheckerboard(SkCanvas* canvas,
                             SkColor c1,
                             SkColor c2,
                             int size) {
  SkPaint paint;
  paint.setShader(CreateCheckerboardShader(c1, c2, size));
  canvas->drawPaint(paint);
}

static void DrawCheckerboard(SkCanvas* canvas, const SkRect& rect) {
  // Draw a checkerboard
  canvas->save();
  canvas->clipRect(rect);

  auto checkerboard_color =
      SkColorSetARGBInline(64, rand() % 256, rand() % 256, rand() % 256);

  DrawCheckerboard(canvas, checkerboard_color, 0x00000000, 12);
  canvas->restore();

  // Stroke the drawn area
  SkPaint debugPaint;
  debugPaint.setStrokeWidth(8);
  debugPaint.setColor(SkColorSetA(checkerboard_color, 255));
  debugPaint.setStyle(SkPaint::kStroke_Style);
  canvas->drawRect(rect, debugPaint);
}

RasterCache::RasterCache() : checkerboard_images_(false), weak_factory_(this) {}

RasterCache::~RasterCache() {}

RasterCache::Entry::Entry() {
  physical_size.setEmpty();
}

RasterCache::Entry::~Entry() {}

sk_sp<SkImage> RasterCache::GetPrerolledImage(GrContext* context,
                                              SkPicture* picture,
                                              const SkMatrix& ctm,
                                              bool is_complex,
                                              bool will_change) {
  SkScalar scaleX = ctm.getScaleX();
  SkScalar scaleY = ctm.getScaleY();

  SkRect rect = picture->cullRect();

  SkISize physical_size =
      SkISize::Make(rect.width() * scaleX, rect.height() * scaleY);

  if (physical_size.isEmpty())
    return nullptr;

  Entry& entry = cache_[picture->uniqueID()];

  const bool size_matched = entry.physical_size == physical_size;

  entry.used_this_frame = true;
  entry.physical_size = physical_size;

  if (!size_matched) {
    entry.access_count = 1;
    entry.image = nullptr;
    return nullptr;
  }

  entry.access_count++;

  if (entry.access_count >= kRasterThreshold) {
    // Saturate at the threshhold.
    entry.access_count = kRasterThreshold;

    if (!entry.image && !will_change &&
        (is_complex || isWorthRasterizing(picture))) {
      TRACE_EVENT2("flutter", "Rasterize picture layer", "width",
                   physical_size.width(), "height", physical_size.height());
      SkImageInfo info = SkImageInfo::MakeN32Premul(physical_size);
      sk_sp<SkSurface> surface =
          SkSurface::MakeRenderTarget(context, SkBudgeted::kYes, info);
      if (surface) {
        SkCanvas* canvas = surface->getCanvas();
        canvas->clear(SK_ColorTRANSPARENT);
        canvas->scale(scaleX, scaleY);
        canvas->translate(-rect.left(), -rect.top());
        canvas->drawPicture(picture);
        if (checkerboard_images_) {
          DrawCheckerboard(canvas, rect);
        }
        entry.image = surface->makeImageSnapshot();
      }
    }
  }

  return entry.image;
}

void RasterCache::SweepAfterFrame() {
  std::vector<Cache::iterator> dead;

  for (auto it = cache_.begin(); it != cache_.end(); ++it) {
    Entry& entry = it->second;
    if (!entry.used_this_frame)
      dead.push_back(it);
    entry.used_this_frame = false;
  }

  for (auto it : dead)
    cache_.erase(it);
}

void RasterCache::Clear() {
  cache_.clear();
}

void RasterCache::SetCheckboardCacheImages(bool checkerboard) {
  if (checkerboard_images_ == checkerboard) {
    return;
  }

  checkerboard_images_ = checkerboard;

  // Clear all existing entries so previously rasterized items (with or without
  // a checkerboard) will be refreshed in subsequent passes.
  Clear();
}

}  // namespace flow