flutter_flutter/flow/layers/opacity_layer.cc

// Copyright 2013 The Flutter 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/layers/opacity_layer.h"

#include "flutter/fml/trace_event.h"
#include "third_party/skia/include/core/SkPaint.h"

namespace flutter {

// The OpacityLayer has no real "elevation", but we want to avoid Z-fighting
// when using the system compositor.  Choose a small but non-zero value for
// this.
constexpr float kOpacityElevationWhenUsingSystemCompositor = 0.01f;

OpacityLayer::OpacityLayer(SkAlpha alpha, const SkPoint& offset)
    : alpha_(alpha), offset_(offset) {
  // Ensure OpacityLayer has only one direct child.
  //
  // This is needed to ensure that retained rendering can always be applied to
  // save the costly saveLayer.
  //
  // Any children will be actually added as children of this empty
  // ContainerLayer.
  ContainerLayer::Add(std::make_shared<ContainerLayer>());
}

void OpacityLayer::Add(std::shared_ptr<Layer> layer) {
  GetChildContainer()->Add(std::move(layer));
}

void OpacityLayer::Preroll(PrerollContext* context, const SkMatrix& matrix) {
  TRACE_EVENT0("flutter", "OpacityLayer::Preroll");

  ContainerLayer* container = GetChildContainer();
  FML_DCHECK(!container->layers().empty());  // OpacityLayer can't be a leaf.

  const bool parent_is_opaque = context->is_opaque;
  SkMatrix child_matrix = matrix;
  child_matrix.postTranslate(offset_.fX, offset_.fY);

  total_elevation_ = context->total_elevation;
  context->total_elevation += kOpacityElevationWhenUsingSystemCompositor;
  context->is_opaque = parent_is_opaque && (alpha_ == SK_AlphaOPAQUE);
  context->mutators_stack.PushTransform(
      SkMatrix::MakeTrans(offset_.fX, offset_.fY));
  context->mutators_stack.PushOpacity(alpha_);
  Layer::AutoPrerollSaveLayerState save =
      Layer::AutoPrerollSaveLayerState::Create(context);
  ContainerLayer::Preroll(context, child_matrix);
  context->mutators_stack.Pop();
  context->mutators_stack.Pop();
  context->is_opaque = parent_is_opaque;
  context->total_elevation = total_elevation_;

#if defined(OS_FUCHSIA)
  if (needs_system_composite()) {
    // When using the system compositor, do not include the offset since we
    // are rendering as a separate piece of geometry and the offset will be
    // baked into that geometry's transform.
    frameRRect_ = SkRRect::MakeRect(paint_bounds());
    set_paint_bounds(SkRect::MakeEmpty());
  } else
#endif
  {
    set_paint_bounds(paint_bounds().makeOffset(offset_.fX, offset_.fY));
    if (!context->has_platform_view && context->raster_cache &&
        SkRect::Intersects(context->cull_rect, paint_bounds())) {
      SkMatrix ctm = child_matrix;
#ifndef SUPPORT_FRACTIONAL_TRANSLATION
      ctm = RasterCache::GetIntegralTransCTM(ctm);
#endif
      context->raster_cache->Prepare(context, container, ctm);
    }
  }
}

void OpacityLayer::Paint(PaintContext& context) const {
  TRACE_EVENT0("flutter", "OpacityLayer::Paint");
  FML_DCHECK(needs_painting());

  SkPaint paint;
  paint.setAlpha(alpha_);

  SkAutoCanvasRestore save(context.internal_nodes_canvas, true);
  context.internal_nodes_canvas->translate(offset_.fX, offset_.fY);

#ifndef SUPPORT_FRACTIONAL_TRANSLATION
  context.internal_nodes_canvas->setMatrix(RasterCache::GetIntegralTransCTM(
      context.leaf_nodes_canvas->getTotalMatrix()));
#endif

  if (context.raster_cache) {
    ContainerLayer* container = GetChildContainer();
    const SkMatrix& ctm = context.leaf_nodes_canvas->getTotalMatrix();
    RasterCacheResult child_cache = context.raster_cache->Get(container, ctm);
    if (child_cache.is_valid()) {
      child_cache.draw(*context.leaf_nodes_canvas, &paint);
      return;
    }
  }

  // Skia may clip the content with saveLayerBounds (although it's not a
  // guaranteed clip). So we have to provide a big enough saveLayerBounds. To do
  // so, we first remove the offset from paint bounds since it's already in the
  // matrix. Then we round out the bounds because of our
  // RasterCache::GetIntegralTransCTM optimization.
  //
  // Note that the following lines are only accessible when the raster cache is
  // not available (e.g., when we're using the software backend in golden
  // tests).
  SkRect saveLayerBounds;
  paint_bounds()
      .makeOffset(-offset_.fX, -offset_.fY)
      .roundOut(&saveLayerBounds);

  Layer::AutoSaveLayer save_layer =
      Layer::AutoSaveLayer::Create(context, saveLayerBounds, &paint);
  PaintChildren(context);
}

#if defined(OS_FUCHSIA)

void OpacityLayer::UpdateScene(SceneUpdateContext& context) {
  FML_DCHECK(needs_system_composite());
  TRACE_EVENT0("flutter", "OpacityLayer::UpdateScene");

  ContainerLayer* container = GetChildContainer();
  FML_DCHECK(!container->layers().empty());  // OpacityLayer can't be a leaf.

  SceneUpdateContext::Transform transform(
      context, SkMatrix::MakeTrans(offset_.fX, offset_.fY));

  // Retained rendering: speedup by reusing a retained entity node if possible.
  // When an entity node is reused, no paint layer is added to the frame so we
  // won't call PhysicalShapeLayer::Paint.
  LayerRasterCacheKey key(unique_id(), context.Matrix());
  if (context.HasRetainedNode(key)) {
    TRACE_EVENT_INSTANT0("flutter", "retained layer cache hit");
    const scenic::EntityNode& retained_node = context.GetRetainedNode(key);
    FML_DCHECK(context.top_entity());
    FML_DCHECK(retained_node.session() == context.session());
    context.top_entity()->embedder_node().AddChild(retained_node);
    return;
  }

  TRACE_EVENT_INSTANT0("flutter", "cache miss, creating");
  // If we can't find an existing retained surface, create one.
  SceneUpdateContext::Frame frame(
      context, frameRRect_, SK_ColorTRANSPARENT, alpha_,
      kOpacityElevationWhenUsingSystemCompositor, total_elevation_, this);
  frame.AddPaintLayer(container);

  UpdateSceneChildren(context);
}

#endif  // defined(OS_FUCHSIA)

ContainerLayer* OpacityLayer::GetChildContainer() const {
  FML_DCHECK(layers().size() == 1);

  return static_cast<ContainerLayer*>(layers()[0].get());
}

}  // namespace flutter