1/*
2 * Copyright (C) 2012 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#ifndef ANDROID_HWUI_PATH_TESSELLATOR_H
18#define ANDROID_HWUI_PATH_TESSELLATOR_H
19
20#include "Matrix.h"
21#include "Rect.h"
22#include "Vertex.h"
23#include "VertexBuffer.h"
24
25#include <algorithm>
26#include <vector>
27
28class SkPath;
29class SkPaint;
30
31namespace android {
32namespace uirenderer {
33
34/**
35 * Structure used for threshold values in outline path tessellation.
36 *
37 * TODO: PaintInfo should store one of this object, and initialized all values in constructor
38 * depending on its type (point, line or path).
39 */
40struct PathApproximationInfo {
41    PathApproximationInfo(float invScaleX, float invScaleY, float pixelThreshold)
42        : thresholdSquared(pixelThreshold * pixelThreshold)
43        , sqrInvScaleX(invScaleX * invScaleX)
44        , sqrInvScaleY(invScaleY * invScaleY)
45        , thresholdForConicQuads(pixelThreshold * std::min(invScaleX, invScaleY) / 2.0f) {
46    };
47
48    const float thresholdSquared;
49    const float sqrInvScaleX;
50    const float sqrInvScaleY;
51    const float thresholdForConicQuads;
52};
53
54class PathTessellator {
55public:
56    /**
57     * Populates scaleX and scaleY with the 'tessellation scale' of the transform - the effective X
58     * and Y scales that tessellation will take into account when generating the 1.0 pixel thick
59     * ramp.
60     *
61     * Two instances of the same shape (size, paint, etc.) will only generate the same vertices if
62     * their tessellation scales are equal.
63     */
64    static void extractTessellationScales(const Matrix4& transform, float* scaleX, float* scaleY);
65
66    /**
67     * Populates a VertexBuffer with a tessellated approximation of the input convex path, as a single
68     * triangle strip. Note: joins are not currently supported.
69     *
70     * @param path The path to be approximated
71     * @param paint The paint the path will be drawn with, indicating AA, painting style
72     *        (stroke vs fill), stroke width, stroke cap & join style, etc.
73     * @param transform The transform the path is to be drawn with, used to drive stretch-aware path
74     *        vertex approximation, and correct AA ramp offsetting.
75     * @param vertexBuffer The output buffer
76     */
77    static void tessellatePath(const SkPath& path, const SkPaint* paint,
78            const mat4& transform, VertexBuffer& vertexBuffer);
79
80    /**
81     * Populates a VertexBuffer with a tessellated approximation of points as a single triangle
82     * strip (with degenerate tris separating), respecting the shape defined by the paint cap.
83     *
84     * @param points The center vertices of the points to be drawn
85     * @param count The number of floats making up the point vertices
86     * @param paint The paint the points will be drawn with indicating AA, stroke width & cap
87     * @param transform The transform the points will be drawn with, used to drive stretch-aware path
88     *        vertex approximation, and correct AA ramp offsetting
89     * @param vertexBuffer The output buffer
90     */
91    static void tessellatePoints(const float* points, int count, const SkPaint* paint,
92            const mat4& transform, VertexBuffer& vertexBuffer);
93
94    /**
95     * Populates a VertexBuffer with a tessellated approximation of lines as a single triangle
96     * strip (with degenerate tris separating).
97     *
98     * @param points Pairs of endpoints defining the lines to be drawn
99     * @param count The number of floats making up the line vertices
100     * @param paint The paint the lines will be drawn with indicating AA, stroke width & cap
101     * @param transform The transform the points will be drawn with, used to drive stretch-aware path
102     *        vertex approximation, and correct AA ramp offsetting
103     * @param vertexBuffer The output buffer
104     */
105    static void tessellateLines(const float* points, int count, const SkPaint* paint,
106            const mat4& transform, VertexBuffer& vertexBuffer);
107
108    /**
109     * Approximates a convex outline into a clockwise Vector of 2d vertices.
110     *
111     * @param path The outline to be approximated
112     * @param threshold The threshold of acceptable error (in pixels) when approximating
113     * @param outputVertices An empty Vector which will be populated with the output
114     */
115    static bool approximatePathOutlineVertices(const SkPath &path, float threshold,
116            std::vector<Vertex> &outputVertices);
117
118private:
119    static bool approximatePathOutlineVertices(const SkPath &path, bool forceClose,
120            const PathApproximationInfo& approximationInfo, std::vector<Vertex> &outputVertices);
121
122/*
123  endpoints a & b,
124  control c
125 */
126    static void recursiveQuadraticBezierVertices(
127            float ax, float ay,
128            float bx, float by,
129            float cx, float cy,
130            const PathApproximationInfo& approximationInfo,
131            std::vector<Vertex> &outputVertices, int depth = 0);
132
133/*
134  endpoints p1, p2
135  control c1, c2
136 */
137    static void recursiveCubicBezierVertices(
138            float p1x, float p1y,
139            float c1x, float c1y,
140            float p2x, float p2y,
141            float c2x, float c2y,
142            const PathApproximationInfo& approximationInfo,
143            std::vector<Vertex> &outputVertices, int depth = 0);
144};
145
146}; // namespace uirenderer
147}; // namespace android
148
149#endif // ANDROID_HWUI_PATH_TESSELLATOR_H
150