flow/layers/physical_shape_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/physical_shape_layer.h"

#include "flutter/flow/paint_utils.h"
#include "third_party/skia/include/utils/SkShadowUtils.h"

namespace flutter {

const SkScalar kLightHeight = 600;
const SkScalar kLightRadius = 800;

PhysicalShapeLayer::PhysicalShapeLayer(SkColor color,
                                       SkColor shadow_color,
                                       float elevation,
                                       const SkPath& path,
                                       Clip clip_behavior)
    : color_(color),
      shadow_color_(shadow_color),
      elevation_(elevation),
      path_(path),
      clip_behavior_(clip_behavior) {}

void PhysicalShapeLayer::Diff(DiffContext* context, const Layer* old_layer) {
  DiffContext::AutoSubtreeRestore subtree(context);
  auto* prev = static_cast<const PhysicalShapeLayer*>(old_layer);
  if (!context->IsSubtreeDirty()) {
    FML_DCHECK(prev);
    if (color_ != prev->color_ || shadow_color_ != prev->shadow_color_ ||
        elevation_ != prev->elevation() || path_ != prev->path_ ||
        clip_behavior_ != prev->clip_behavior_) {
      context->MarkSubtreeDirty(context->GetOldLayerPaintRegion(old_layer));
    }
  }

  SkRect bounds;
  if (elevation_ == 0) {
    bounds = path_.getBounds();
  } else {
    bounds = ComputeShadowBounds(path_, elevation_,
                                 context->frame_device_pixel_ratio(),
                                 context->GetTransform());
  }

  context->AddLayerBounds(bounds);

  // Only push cull rect if there is clip.
  if (clip_behavior_ == Clip::none || context->PushCullRect(bounds)) {
    DiffChildren(context, prev);
  }
  context->SetLayerPaintRegion(this, context->CurrentSubtreeRegion());
}

void PhysicalShapeLayer::Preroll(PrerollContext* context,
                                 const SkMatrix& matrix) {
  TRACE_EVENT0("flutter", "PhysicalShapeLayer::Preroll");
  Layer::AutoPrerollSaveLayerState save =
      Layer::AutoPrerollSaveLayerState::Create(context, UsesSaveLayer());

  SkRect child_paint_bounds;
  PrerollChildren(context, matrix, &child_paint_bounds);

  if (elevation_ == 0) {
    set_paint_bounds(path_.getBounds());
  } else {
    // We will draw the shadow in Paint(), so add some margin to the paint
    // bounds to leave space for the shadow. We fill this whole region and clip
    // children to it so we don't need to join the child paint bounds.
    set_paint_bounds(ComputeShadowBounds(
        path_, elevation_, context->frame_device_pixel_ratio, matrix));
  }
}

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

  if (elevation_ != 0) {
    DrawShadow(context.leaf_nodes_canvas, path_, shadow_color_, elevation_,
               SkColorGetA(color_) != 0xff, context.frame_device_pixel_ratio);
  }

  // Call drawPath without clip if possible for better performance.
  SkPaint paint;
  paint.setColor(color_);
  paint.setAntiAlias(true);
  if (clip_behavior_ != Clip::antiAliasWithSaveLayer) {
    context.leaf_nodes_canvas->drawPath(path_, paint);
  }

  int saveCount = context.internal_nodes_canvas->save();
  switch (clip_behavior_) {
    case Clip::hardEdge:
      context.internal_nodes_canvas->clipPath(path_, false);
      break;
    case Clip::antiAlias:
      context.internal_nodes_canvas->clipPath(path_, true);
      break;
    case Clip::antiAliasWithSaveLayer: {
      TRACE_EVENT0("flutter", "Canvas::saveLayer");
      context.internal_nodes_canvas->clipPath(path_, true);
      context.internal_nodes_canvas->saveLayer(paint_bounds(), nullptr);
    } break;
    case Clip::none:
      break;
  }

  if (UsesSaveLayer()) {
    // If we want to avoid the bleeding edge artifact
    // (https://github.com/flutter/flutter/issues/18057#issue-328003931)
    // using saveLayer, we have to call drawPaint instead of drawPath as
    // anti-aliased drawPath will always have such artifacts.
    context.leaf_nodes_canvas->drawPaint(paint);
  }

  PaintChildren(context);

  context.internal_nodes_canvas->restoreToCount(saveCount);

  if (UsesSaveLayer()) {
    if (context.checkerboard_offscreen_layers) {
      DrawCheckerboard(context.internal_nodes_canvas, paint_bounds());
    }
  }
}

SkRect PhysicalShapeLayer::ComputeShadowBounds(const SkPath& path,
                                               float elevation,
                                               SkScalar dpr,
                                               const SkMatrix& ctm) {
  SkRect shadow_bounds(path.getBounds());
  SkShadowUtils::GetLocalBounds(
      ctm, path, SkPoint3::Make(0, 0, dpr * elevation),
      SkPoint3::Make(0, -1, 1), kLightRadius / kLightHeight,
      SkShadowFlags::kDirectionalLight_ShadowFlag, &shadow_bounds);
  return shadow_bounds;
}

void PhysicalShapeLayer::DrawShadow(SkCanvas* canvas,
                                    const SkPath& path,
                                    SkColor color,
                                    float elevation,
                                    bool transparentOccluder,
                                    SkScalar dpr) {
  const SkScalar kAmbientAlpha = 0.039f;
  const SkScalar kSpotAlpha = 0.25f;

  uint32_t flags = transparentOccluder
                       ? SkShadowFlags::kTransparentOccluder_ShadowFlag
                       : SkShadowFlags::kNone_ShadowFlag;
  flags |= SkShadowFlags::kDirectionalLight_ShadowFlag;
  SkColor inAmbient = SkColorSetA(color, kAmbientAlpha * SkColorGetA(color));
  SkColor inSpot = SkColorSetA(color, kSpotAlpha * SkColorGetA(color));
  SkColor ambientColor, spotColor;
  SkShadowUtils::ComputeTonalColors(inAmbient, inSpot, &ambientColor,
                                    &spotColor);
  SkShadowUtils::DrawShadow(canvas, path, SkPoint3::Make(0, 0, dpr * elevation),
                            SkPoint3::Make(0, -1, 1),
                            kLightRadius / kLightHeight, ambientColor,
                            spotColor, flags);
}

}  // namespace flutter