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[Impeller] Avoid allocating path for dashed lines (#169881)
We use the new algorithmically generated `PathSource` mechanism for generating dashed lines to avoid allocating a growable path object.
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10 files changed

+286
-35
lines changed

‎engine/src/flutter/ci/licenses_golden/licenses_flutter

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@@ -51472,6 +51472,8 @@ ORIGIN: ../../../flutter/impeller/geometry/color.cc + ../../../flutter/LICENSE
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ORIGIN: ../../../flutter/impeller/geometry/color.h + ../../../flutter/LICENSE
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ORIGIN: ../../../flutter/impeller/geometry/constants.cc + ../../../flutter/LICENSE
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ORIGIN: ../../../flutter/impeller/geometry/constants.h + ../../../flutter/LICENSE
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ORIGIN: ../../../flutter/impeller/geometry/dashed_line_path_source.cc + ../../../flutter/LICENSE
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ORIGIN: ../../../flutter/impeller/geometry/dashed_line_path_source.h + ../../../flutter/LICENSE
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ORIGIN: ../../../flutter/impeller/geometry/geometry_asserts.h + ../../../flutter/LICENSE
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ORIGIN: ../../../flutter/impeller/geometry/geometry_benchmarks.cc + ../../../flutter/LICENSE
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ORIGIN: ../../../flutter/impeller/geometry/gradient.cc + ../../../flutter/LICENSE
@@ -54496,6 +54498,8 @@ FILE: ../../../flutter/impeller/geometry/color.cc
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FILE: ../../../flutter/impeller/geometry/color.h
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FILE: ../../../flutter/impeller/geometry/constants.cc
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FILE: ../../../flutter/impeller/geometry/constants.h
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FILE: ../../../flutter/impeller/geometry/dashed_line_path_source.cc
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FILE: ../../../flutter/impeller/geometry/dashed_line_path_source.h
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FILE: ../../../flutter/impeller/geometry/geometry_asserts.h
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FILE: ../../../flutter/impeller/geometry/geometry_benchmarks.cc
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FILE: ../../../flutter/impeller/geometry/gradient.cc

‎engine/src/flutter/impeller/display_list/canvas.cc

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@@ -603,6 +603,32 @@ void Canvas::DrawLine(const Point& p0,
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}
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}
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606+
void Canvas::DrawDashedLine(const Point& p0,
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const Point& p1,
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Scalar on_length,
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Scalar off_length,
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const Paint& paint) {
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// Reasons to defer to regular DrawLine:
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// - performance for degenerate and "regular line" cases
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// - length is non-positive - DrawLine will draw appropriate "dot"
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// - off_length is non-positive - no gaps, DrawLine will draw it solid
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// - on_length is negative - invalid dashing
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//
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// Note that a 0 length "on" dash will draw "dot"s every "off" distance
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// apart so we proceed with the dashing process in that case.
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Scalar length = p0.GetDistance(p1);
620+
if (length > 0.0f && on_length >= 0.0f && off_length > 0.0f) {
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Entity entity;
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entity.SetTransform(GetCurrentTransform());
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entity.SetBlendMode(paint.blend_mode);
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StrokeDashedLineGeometry geom(p0, p1, on_length, off_length, paint.stroke);
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AddRenderEntityWithFiltersToCurrentPass(entity, &geom, paint);
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} else {
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DrawLine(p0, p1, paint);
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}
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}
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void Canvas::DrawRect(const Rect& rect, const Paint& paint) {
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if (AttemptDrawBlurredRRect(rect, {}, paint)) {
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return;

‎engine/src/flutter/impeller/display_list/canvas.h

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@@ -199,6 +199,12 @@ class Canvas {
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const Paint& paint,
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bool reuse_depth = false);
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void DrawDashedLine(const Point& p0,
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const Point& p1,
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Scalar on_length,
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Scalar off_length,
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const Paint& paint);
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void DrawRect(const Rect& rect, const Paint& paint);
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void DrawOval(const Rect& rect, const Paint& paint);

‎engine/src/flutter/impeller/display_list/dl_dispatcher.cc

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@@ -12,7 +12,6 @@
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#include "display_list/dl_sampling_options.h"
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#include "display_list/effects/dl_image_filter.h"
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#include "display_list/geometry/dl_path_builder.h"
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#include "flutter/fml/logging.h"
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#include "fml/closure.h"
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#include "impeller/core/formats.h"
@@ -547,46 +546,14 @@ void DlDispatcherBase::drawLine(const DlPoint& p0, const DlPoint& p1) {
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GetCanvas().DrawLine(p0, p1, paint_);
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}
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// |flutter::DlOpReceiver|
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void DlDispatcherBase::drawDashedLine(const DlPoint& p0,
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const DlPoint& p1,
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DlScalar on_length,
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DlScalar off_length) {
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AUTO_DEPTH_WATCHER(1u);
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Scalar length = p0.GetDistance(p1);
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// Reasons to defer to regular DrawLine:
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// length is non-positive - drawLine will draw appropriate "dot"
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// off_length is non-positive - no gaps, drawLine will draw it solid
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// on_length is negative - invalid dashing
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// Note that a 0 length "on" dash will draw "dot"s every "off" distance
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// apart
563-
if (length > 0.0f && on_length >= 0.0f && off_length > 0.0f) {
564-
Point delta = (p1 - p0) / length; // length > 0 already tested
565-
flutter::DlPathBuilder builder;
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Scalar consumed = 0.0f;
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while (consumed < length) {
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builder.MoveTo(p0 + delta * consumed);
570-
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Scalar dash_end = consumed + on_length;
572-
if (dash_end < length) {
573-
builder.LineTo(p0 + delta * dash_end);
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} else {
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builder.LineTo(p1);
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// Should happen anyway due to the math, but let's make it explicit
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// in case of bit errors. We're done with this line.
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break;
579-
}
580-
581-
consumed = dash_end + off_length;
582-
}
583-
584-
Paint stroke_paint = paint_;
585-
stroke_paint.style = Paint::Style::kStroke;
586-
GetCanvas().DrawPath(builder.TakePath(), stroke_paint);
587-
} else {
588-
drawLine(p0, p1);
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}
556+
GetCanvas().DrawDashedLine(p0, p1, on_length, off_length, paint_);
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}
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592559
// |flutter::DlOpReceiver|

‎engine/src/flutter/impeller/entity/geometry/stroke_path_geometry.cc

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@@ -846,4 +846,17 @@ const PathSource& StrokeDiffRoundRectGeometry::GetSource() const {
846846
return source_;
847847
}
848848

849+
StrokeDashedLineGeometry::StrokeDashedLineGeometry(
850+
Point p0,
851+
Point p1,
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Scalar on_length,
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Scalar off_length,
854+
const StrokeParameters& parameters)
855+
: StrokePathSourceGeometry(parameters),
856+
source_(p0, p1, on_length, off_length) {}
857+
858+
const PathSource& StrokeDashedLineGeometry::GetSource() const {
859+
return source_;
860+
}
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} // namespace impeller

‎engine/src/flutter/impeller/entity/geometry/stroke_path_geometry.h

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@@ -6,6 +6,7 @@
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#define FLUTTER_IMPELLER_ENTITY_GEOMETRY_STROKE_PATH_GEOMETRY_H_
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#include "impeller/entity/geometry/geometry.h"
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#include "impeller/geometry/dashed_line_path_source.h"
910
#include "impeller/geometry/matrix.h"
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#include "impeller/geometry/path_source.h"
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#include "impeller/geometry/stroke_parameters.h"
@@ -126,6 +127,25 @@ class StrokeDiffRoundRectGeometry final : public StrokePathSourceGeometry {
126127
const DiffRoundRectPathSource source_;
127128
};
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130+
/// @brief A Geometry that produces fillable vertices representing the
131+
/// stroked outline of a |DlPath| object using the
132+
/// |StrokePathSourceGeometry| base class and a |DlPath| object
133+
/// to perform path iteration.
134+
class StrokeDashedLineGeometry final : public StrokePathSourceGeometry {
135+
public:
136+
StrokeDashedLineGeometry(Point p0,
137+
Point p1,
138+
Scalar on_length,
139+
Scalar off_length,
140+
const StrokeParameters& parameters);
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protected:
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const PathSource& GetSource() const override;
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private:
146+
const DashedLinePathSource source_;
147+
};
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129149
} // namespace impeller
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#endif // FLUTTER_IMPELLER_ENTITY_GEOMETRY_STROKE_PATH_GEOMETRY_H_

‎engine/src/flutter/impeller/geometry/BUILD.gn

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@@ -10,6 +10,8 @@ impeller_component("geometry") {
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"color.h",
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"constants.cc",
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"constants.h",
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"dashed_line_path_source.cc",
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"dashed_line_path_source.h",
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"gradient.cc",
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"gradient.h",
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"half.h",

‎engine/src/flutter/impeller/geometry/dashed_line_path_source.cc

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@@ -0,0 +1,68 @@
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// Copyright 2013 The Flutter Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
3+
// found in the LICENSE file.
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5+
#include "impeller/geometry/dashed_line_path_source.h"
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7+
namespace impeller {
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DashedLinePathSource::DashedLinePathSource(Point p0,
10+
Point p1,
11+
Scalar on_length,
12+
Scalar off_length)
13+
: p0_(p0), p1_(p1), on_length_(on_length), off_length_(off_length) {}
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15+
DashedLinePathSource::~DashedLinePathSource() = default;
16+
17+
FillType DashedLinePathSource::GetFillType() const {
18+
return FillType::kNonZero;
19+
}
20+
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Rect DashedLinePathSource::GetBounds() const {
22+
return Rect::MakeLTRB(p0_.x, p0_.y, p1_.x, p1_.y).GetPositive();
23+
}
24+
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bool DashedLinePathSource::IsConvex() const {
26+
return false;
27+
}
28+
29+
void DashedLinePathSource::Dispatch(PathReceiver& receiver) const {
30+
// Exceptional conditions:
31+
// - length is non-positive - result will draw only a "dot"
32+
// - off_length is non-positive - no gaps, result is a solid line
33+
// - on_length is negative - invalid dashing
34+
// Note that a 0 length "on" dash will draw "dot"s every "off" distance
35+
// apart so we still generate the dashing for that case.
36+
//
37+
// Note that Canvas will detect these conditions and use its own DrawLine
38+
// method directly for performance reasons for a single line, but in case
39+
// someone uses this PathSource with these exceptional cases, we degenerate
40+
// gracefully into a single line segment path description below.
41+
Scalar length = p0_.GetDistance(p1_);
42+
if (length > 0.0f && on_length_ >= 0.0f && off_length_ > 0.0f) {
43+
Point delta = (p1_ - p0_) / length; // length > 0 already verified
44+
45+
Scalar consumed = 0.0f;
46+
while (consumed < length) {
47+
receiver.MoveTo(p0_ + delta * consumed, false);
48+
49+
Scalar dash_end = consumed + on_length_;
50+
if (dash_end < length) {
51+
receiver.LineTo(p0_ + delta * dash_end);
52+
} else {
53+
receiver.LineTo(p1_);
54+
// Should happen anyway due to the math, but let's make it explicit
55+
// in case of bit errors. We're done with this line.
56+
break;
57+
}
58+
59+
consumed = dash_end + off_length_;
60+
}
61+
} else {
62+
receiver.MoveTo(p0_, false);
63+
receiver.LineTo(p1_);
64+
}
65+
receiver.PathEnd();
66+
}
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68+
} // namespace impeller

‎engine/src/flutter/impeller/geometry/dashed_line_path_source.h

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@@ -0,0 +1,42 @@
1+
// Copyright 2013 The Flutter Authors. All rights reserved.
2+
// Use of this source code is governed by a BSD-style license that can be
3+
// found in the LICENSE file.
4+
5+
#ifndef FLUTTER_IMPELLER_GEOMETRY_DASHED_LINE_PATH_SOURCE_H_
6+
#define FLUTTER_IMPELLER_GEOMETRY_DASHED_LINE_PATH_SOURCE_H_
7+
8+
#include "flutter/impeller/geometry/path_source.h"
9+
#include "flutter/impeller/geometry/point.h"
10+
#include "flutter/impeller/geometry/scalar.h"
11+
12+
namespace impeller {
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14+
/// @brief A PathSource that generates the various segments of a dashed line.
15+
class DashedLinePathSource : public PathSource {
16+
public:
17+
DashedLinePathSource(Point p0, Point p1, Scalar on_length, Scalar off_length);
18+
19+
~DashedLinePathSource();
20+
21+
// |PathSource|
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FillType GetFillType() const override;
23+
24+
// |PathSource|
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Rect GetBounds() const override;
26+
27+
// |PathSource|
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bool IsConvex() const override;
29+
30+
// |PathSource|
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void Dispatch(PathReceiver& receiver) const override;
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33+
private:
34+
const Point p0_;
35+
const Point p1_;
36+
const Scalar on_length_;
37+
const Scalar off_length_;
38+
};
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40+
} // namespace impeller
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42+
#endif // FLUTTER_IMPELLER_GEOMETRY_DASHED_LINE_PATH_SOURCE_H_

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