Flutter Impeller
path_component.h
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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_PATH_COMPONENT_H_
6 #define FLUTTER_IMPELLER_GEOMETRY_PATH_COMPONENT_H_
7 
8 #include <functional>
9 #include <type_traits>
10 #include <variant>
11 #include <vector>
12 
14 #include "impeller/geometry/rect.h"
16 
17 namespace impeller {
18 
19 // The default tolerance value for QuadraticCurveComponent::AppendPolylinePoints
20 // and CubicCurveComponent::AppendPolylinePoints. It also impacts the number of
21 // quadratics created when flattening a cubic curve to a polyline.
22 //
23 // Smaller numbers mean more points. This number seems suitable for particularly
24 // curvy curves at scales close to 1.0. As the scale increases, this number
25 // should be divided by Matrix::GetMaxBasisLength to avoid generating too few
26 // points for the given scale.
27 static constexpr Scalar kDefaultCurveTolerance = .1f;
28 
32 
34 
35  LinearPathComponent(Point ap1, Point ap2) : p1(ap1), p2(ap2) {}
36 
37  Point Solve(Scalar time) const;
38 
39  void AppendPolylinePoints(std::vector<Point>& points) const;
40 
41  std::vector<Point> Extrema() const;
42 
43  bool operator==(const LinearPathComponent& other) const {
44  return p1 == other.p1 && p2 == other.p2;
45  }
46 
47  std::optional<Vector2> GetStartDirection() const;
48 
49  std::optional<Vector2> GetEndDirection() const;
50 };
51 
52 // A component that represets a Quadratic Bézier curve.
54  // Start point.
56  // Control point.
58  // End point.
60 
62 
64  : p1(ap1), cp(acp), p2(ap2) {}
65 
66  Point Solve(Scalar time) const;
67 
68  Point SolveDerivative(Scalar time) const;
69 
70  // Uses the algorithm described by Raph Levien in
71  // https://raphlinus.github.io/graphics/curves/2019/12/23/flatten-quadbez.html.
72  //
73  // The algorithm has several benefits:
74  // - It does not require elevation to cubics for processing.
75  // - It generates fewer and more accurate points than recursive subdivision.
76  // - Each turn of the core iteration loop has no dependencies on other turns,
77  // making it trivially parallelizable.
78  //
79  // See also the implementation in kurbo: https://github.com/linebender/kurbo.
80  void AppendPolylinePoints(Scalar scale_factor,
81  std::vector<Point>& points) const;
82 
83  using PointProc = std::function<void(const Point& point)>;
84 
85  void ToLinearPathComponents(Scalar scale_factor, const PointProc& proc) const;
86 
87  std::vector<Point> Extrema() const;
88 
89  bool operator==(const QuadraticPathComponent& other) const {
90  return p1 == other.p1 && cp == other.cp && p2 == other.p2;
91  }
92 
93  std::optional<Vector2> GetStartDirection() const;
94 
95  std::optional<Vector2> GetEndDirection() const;
96 };
97 
98 // A component that represets a Cubic Bézier curve.
100  // Start point.
102  // The first control point.
104  // The second control point.
106  // End point.
108 
110 
112  : p1(q.p1),
113  cp1(q.p1 + (q.cp - q.p1) * (2.0 / 3.0)),
114  cp2(q.p2 + (q.cp - q.p2) * (2.0 / 3.0)),
115  p2(q.p2) {}
116 
117  CubicPathComponent(Point ap1, Point acp1, Point acp2, Point ap2)
118  : p1(ap1), cp1(acp1), cp2(acp2), p2(ap2) {}
119 
120  Point Solve(Scalar time) const;
121 
122  Point SolveDerivative(Scalar time) const;
123 
124  // This method approximates the cubic component with quadratics, and then
125  // generates a polyline from those quadratics.
126  //
127  // See the note on QuadraticPathComponent::AppendPolylinePoints for
128  // references.
129  void AppendPolylinePoints(Scalar scale, std::vector<Point>& points) const;
130 
131  std::vector<Point> Extrema() const;
132 
133  using PointProc = std::function<void(const Point& point)>;
134 
135  void ToLinearPathComponents(Scalar scale, const PointProc& proc) const;
136 
138 
139  bool operator==(const CubicPathComponent& other) const {
140  return p1 == other.p1 && cp1 == other.cp1 && cp2 == other.cp2 &&
141  p2 == other.p2;
142  }
143 
144  std::optional<Vector2> GetStartDirection() const;
145 
146  std::optional<Vector2> GetEndDirection() const;
147 
148  private:
149  QuadraticPathComponent Lower() const;
150 };
151 
154  bool is_closed = false;
155 
157 
158  explicit ContourComponent(Point p, bool is_closed = false)
160 
161  bool operator==(const ContourComponent& other) const {
162  return destination == other.destination && is_closed == other.is_closed;
163  }
164 };
165 
166 using PathComponentVariant = std::variant<std::monostate,
167  const LinearPathComponent*,
168  const QuadraticPathComponent*,
170 
172  std::optional<Vector2> operator()(const LinearPathComponent* component);
173  std::optional<Vector2> operator()(const QuadraticPathComponent* component);
174  std::optional<Vector2> operator()(const CubicPathComponent* component);
175  std::optional<Vector2> operator()(std::monostate monostate) {
176  return std::nullopt;
177  }
178 };
179 
181  std::optional<Vector2> operator()(const LinearPathComponent* component);
182  std::optional<Vector2> operator()(const QuadraticPathComponent* component);
183  std::optional<Vector2> operator()(const CubicPathComponent* component);
184  std::optional<Vector2> operator()(std::monostate monostate) {
185  return std::nullopt;
186  }
187 };
188 
189 static_assert(!std::is_polymorphic<LinearPathComponent>::value);
190 static_assert(!std::is_polymorphic<QuadraticPathComponent>::value);
191 static_assert(!std::is_polymorphic<CubicPathComponent>::value);
192 
193 } // namespace impeller
194 
195 #endif // FLUTTER_IMPELLER_GEOMETRY_PATH_COMPONENT_H_
point.h
impeller::LinearPathComponent
Definition: path_component.h:29
impeller::Scalar
float Scalar
Definition: scalar.h:18
impeller::kDefaultCurveTolerance
static constexpr Scalar kDefaultCurveTolerance
Definition: path_component.h:27
impeller::PathComponentStartDirectionVisitor::operator()
std::optional< Vector2 > operator()(std::monostate monostate)
Definition: path_component.h:175
impeller::CubicPathComponent::Subsegment
CubicPathComponent Subsegment(Scalar t0, Scalar t1) const
Definition: path_component.cc:208
impeller::CubicPathComponent::p1
Point p1
Definition: path_component.h:101
impeller::QuadraticPathComponent::operator==
bool operator==(const QuadraticPathComponent &other) const
Definition: path_component.h:89
impeller::LinearPathComponent::p2
Point p2
Definition: path_component.h:31
impeller::QuadraticPathComponent::p1
Point p1
Definition: path_component.h:55
impeller::CubicPathComponent::GetStartDirection
std::optional< Vector2 > GetStartDirection() const
Definition: path_component.cc:330
impeller::CubicPathComponent::cp2
Point cp2
Definition: path_component.h:105
impeller::CubicPathComponent::AppendPolylinePoints
void AppendPolylinePoints(Scalar scale, std::vector< Point > &points) const
Definition: path_component.cc:196
impeller::LinearPathComponent::AppendPolylinePoints
void AppendPolylinePoints(std::vector< Point > &points) const
Definition: path_component.cc:62
impeller::QuadraticPathComponent::cp
Point cp
Definition: path_component.h:57
impeller::QuadraticPathComponent::GetStartDirection
std::optional< Vector2 > GetStartDirection() const
Definition: path_component.cc:162
impeller::PathComponentEndDirectionVisitor
Definition: path_component.h:180
impeller::ContourComponent::ContourComponent
ContourComponent(Point p, bool is_closed=false)
Definition: path_component.h:158
impeller::CubicPathComponent::Solve
Point Solve(Scalar time) const
Definition: path_component.cc:182
impeller::PathComponentStartDirectionVisitor::operator()
std::optional< Vector2 > operator()(const LinearPathComponent *component)
Definition: path_component.cc:356
impeller::QuadraticPathComponent::GetEndDirection
std::optional< Vector2 > GetEndDirection() const
Definition: path_component.cc:172
impeller::ContourComponent::operator==
bool operator==(const ContourComponent &other) const
Definition: path_component.h:161
impeller::QuadraticPathComponent::ToLinearPathComponents
void ToLinearPathComponents(Scalar scale_factor, const PointProc &proc) const
Definition: path_component.cc:114
impeller::LinearPathComponent::LinearPathComponent
LinearPathComponent()
Definition: path_component.h:33
impeller::QuadraticPathComponent::PointProc
std::function< void(const Point &point)> PointProc
Definition: path_component.h:83
impeller::QuadraticPathComponent::SolveDerivative
Point SolveDerivative(Scalar time) const
Definition: path_component.cc:94
impeller::CubicPathComponent::cp1
Point cp1
Definition: path_component.h:103
impeller::LinearPathComponent::p1
Point p1
Definition: path_component.h:30
impeller::QuadraticPathComponent::QuadraticPathComponent
QuadraticPathComponent(Point ap1, Point acp, Point ap2)
Definition: path_component.h:63
impeller::LinearPathComponent::GetStartDirection
std::optional< Vector2 > GetStartDirection() const
Definition: path_component.cc:73
impeller::ContourComponent::is_closed
bool is_closed
Definition: path_component.h:154
impeller::QuadraticPathComponent::Solve
Point Solve(Scalar time) const
Definition: path_component.cc:87
impeller::LinearPathComponent::operator==
bool operator==(const LinearPathComponent &other) const
Definition: path_component.h:43
impeller::CubicPathComponent::operator==
bool operator==(const CubicPathComponent &other) const
Definition: path_component.h:139
impeller::CubicPathComponent::SolveDerivative
Point SolveDerivative(Scalar time) const
Definition: path_component.cc:189
impeller::LinearPathComponent::LinearPathComponent
LinearPathComponent(Point ap1, Point ap2)
Definition: path_component.h:35
impeller::PathComponentStartDirectionVisitor
Definition: path_component.h:171
impeller::QuadraticPathComponent::Extrema
std::vector< Point > Extrema() const
Definition: path_component.cc:157
impeller::ContourComponent::destination
Point destination
Definition: path_component.h:153
impeller::CubicPathComponent::GetEndDirection
std::optional< Vector2 > GetEndDirection() const
Definition: path_component.cc:343
impeller::CubicPathComponent::CubicPathComponent
CubicPathComponent(const QuadraticPathComponent &q)
Definition: path_component.h:111
impeller::CubicPathComponent::CubicPathComponent
CubicPathComponent()
Definition: path_component.h:109
impeller::CubicPathComponent
Definition: path_component.h:99
scalar.h
impeller::ContourComponent::ContourComponent
ContourComponent()
Definition: path_component.h:156
impeller::CubicPathComponent::ToLinearPathComponents
void ToLinearPathComponents(Scalar scale, const PointProc &proc) const
Definition: path_component.cc:218
impeller::QuadraticPathComponent::AppendPolylinePoints
void AppendPolylinePoints(Scalar scale_factor, std::vector< Point > &points) const
Definition: path_component.cc:106
rect.h
impeller::QuadraticPathComponent::p2
Point p2
Definition: path_component.h:59
impeller::TPoint< Scalar >
impeller::PathComponentEndDirectionVisitor::operator()
std::optional< Vector2 > operator()(const LinearPathComponent *component)
Definition: path_component.cc:380
impeller::QuadraticPathComponent::QuadraticPathComponent
QuadraticPathComponent()
Definition: path_component.h:61
scale
const Scalar scale
Definition: stroke_path_geometry.cc:297
impeller::CubicPathComponent::PointProc
std::function< void(const Point &point)> PointProc
Definition: path_component.h:133
impeller::CubicPathComponent::p2
Point p2
Definition: path_component.h:107
impeller::CubicPathComponent::Extrema
std::vector< Point > Extrema() const
Definition: path_component.cc:312
impeller::PathComponentVariant
std::variant< std::monostate, const LinearPathComponent *, const QuadraticPathComponent *, const CubicPathComponent * > PathComponentVariant
Definition: path_component.h:169
impeller::PathComponentEndDirectionVisitor::operator()
std::optional< Vector2 > operator()(std::monostate monostate)
Definition: path_component.h:184
impeller::ContourComponent
Definition: path_component.h:152
impeller::LinearPathComponent::GetEndDirection
std::optional< Vector2 > GetEndDirection() const
Definition: path_component.cc:80
impeller
Definition: aiks_blur_unittests.cc:20
impeller::QuadraticPathComponent
Definition: path_component.h:53
impeller::LinearPathComponent::Solve
Point Solve(Scalar time) const
Definition: path_component.cc:55
impeller::LinearPathComponent::Extrema
std::vector< Point > Extrema() const
Definition: path_component.cc:69
impeller::CubicPathComponent::CubicPathComponent
CubicPathComponent(Point ap1, Point acp1, Point acp2, Point ap2)
Definition: path_component.h:117