cc/resources/raster_source_helper.cc

// Copyright 2014 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 "cc/resources/raster_source_helper.h"

#include "base/trace_event/trace_event.h"
#include "cc/debug/debug_colors.h"
#include "third_party/skia/include/core/SkCanvas.h"
#include "ui/gfx/geometry/rect_conversions.h"
#include "ui/gfx/skia_util.h"

namespace cc {

void RasterSourceHelper::PrepareForPlaybackToCanvas(
    SkCanvas* canvas,
    const gfx::Rect& canvas_rect,
    const gfx::Rect& source_rect,
    float contents_scale,
    SkColor background_color,
    bool clear_canvas_with_debug_color,
    bool requires_clear) {
  canvas->discard();
  if (clear_canvas_with_debug_color) {
    // Any non-painted areas in the content bounds will be left in this color.
    canvas->clear(DebugColors::NonPaintedFillColor());
  }

  // If this raster source has opaque contents, it is guaranteeing that it will
  // draw an opaque rect the size of the layer.  If it is not, then we must
  // clear this canvas ourselves.
  if (requires_clear) {
    TRACE_EVENT_INSTANT0("cc", "SkCanvas::clear", TRACE_EVENT_SCOPE_THREAD);
    // Clearing is about ~4x faster than drawing a rect even if the content
    // isn't covering a majority of the canvas.
    canvas->clear(SK_ColorTRANSPARENT);
  } else {
    // Even if completely covered, for rasterizations that touch the edge of the
    // layer, we also need to raster the background color underneath the last
    // texel (since the recording won't cover it) and outside the last texel
    // (due to linear filtering when using this texture).
    gfx::Rect content_rect =
        gfx::ToEnclosingRect(gfx::ScaleRect(source_rect, contents_scale));

    // The final texel of content may only be partially covered by a
    // rasterization; this rect represents the content rect that is fully
    // covered by content.
    gfx::Rect deflated_content_rect = content_rect;
    deflated_content_rect.Inset(0, 0, 1, 1);
    if (!deflated_content_rect.Contains(canvas_rect)) {
      if (clear_canvas_with_debug_color) {
        // Any non-painted areas outside of the content bounds are left in
        // this color.  If this is seen then it means that cc neglected to
        // rerasterize a tile that used to intersect with the content rect
        // after the content bounds grew.
        canvas->save();
        canvas->translate(-canvas_rect.x(), -canvas_rect.y());
        canvas->clipRect(gfx::RectToSkRect(content_rect),
                         SkRegion::kDifference_Op);
        canvas->drawColor(DebugColors::MissingResizeInvalidations(),
                          SkXfermode::kSrc_Mode);
        canvas->restore();
      }

      // Drawing at most 2 x 2 x (canvas width + canvas height) texels is 2-3X
      // faster than clearing, so special case this.
      canvas->save();
      canvas->translate(-canvas_rect.x(), -canvas_rect.y());
      gfx::Rect inflated_content_rect = content_rect;
      inflated_content_rect.Inset(0, 0, -1, -1);
      canvas->clipRect(gfx::RectToSkRect(inflated_content_rect),
                       SkRegion::kReplace_Op);
      canvas->clipRect(gfx::RectToSkRect(deflated_content_rect),
                       SkRegion::kDifference_Op);
      canvas->drawColor(background_color, SkXfermode::kSrc_Mode);
      canvas->restore();
    }
  }
}

}  // namespace cc