1/*
2 * Copyright 2011 Google Inc.
3 *
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
6 */
7
8#ifndef GrPathUtils_DEFINED
9#define GrPathUtils_DEFINED
10
11#include "GrPoint.h"
12#include "SkRect.h"
13#include "SkPath.h"
14#include "SkTArray.h"
15
16class SkMatrix;
17
18/**
19 *  Utilities for evaluating paths.
20 */
21namespace GrPathUtils {
22    SkScalar scaleToleranceToSrc(SkScalar devTol,
23                                 const SkMatrix& viewM,
24                                 const SkRect& pathBounds);
25
26    /// Since we divide by tol if we're computing exact worst-case bounds,
27    /// very small tolerances will be increased to gMinCurveTol.
28    int worstCasePointCount(const SkPath&,
29                            int* subpaths,
30                            SkScalar tol);
31
32    /// Since we divide by tol if we're computing exact worst-case bounds,
33    /// very small tolerances will be increased to gMinCurveTol.
34    uint32_t quadraticPointCount(const GrPoint points[], SkScalar tol);
35
36    uint32_t generateQuadraticPoints(const GrPoint& p0,
37                                     const GrPoint& p1,
38                                     const GrPoint& p2,
39                                     SkScalar tolSqd,
40                                     GrPoint** points,
41                                     uint32_t pointsLeft);
42
43    /// Since we divide by tol if we're computing exact worst-case bounds,
44    /// very small tolerances will be increased to gMinCurveTol.
45    uint32_t cubicPointCount(const GrPoint points[], SkScalar tol);
46
47    uint32_t generateCubicPoints(const GrPoint& p0,
48                                 const GrPoint& p1,
49                                 const GrPoint& p2,
50                                 const GrPoint& p3,
51                                 SkScalar tolSqd,
52                                 GrPoint** points,
53                                 uint32_t pointsLeft);
54
55    // A 2x3 matrix that goes from the 2d space coordinates to UV space where
56    // u^2-v = 0 specifies the quad. The matrix is determined by the control
57    // points of the quadratic.
58    class QuadUVMatrix {
59    public:
60        QuadUVMatrix() {};
61        // Initialize the matrix from the control pts
62        QuadUVMatrix(const GrPoint controlPts[3]) { this->set(controlPts); }
63        void set(const GrPoint controlPts[3]);
64
65        /**
66         * Applies the matrix to vertex positions to compute UV coords. This
67         * has been templated so that the compiler can easliy unroll the loop
68         * and reorder to avoid stalling for loads. The assumption is that a
69         * path renderer will have a small fixed number of vertices that it
70         * uploads for each quad.
71         *
72         * N is the number of vertices.
73         * STRIDE is the size of each vertex.
74         * UV_OFFSET is the offset of the UV values within each vertex.
75         * vertices is a pointer to the first vertex.
76         */
77        template <int N, size_t STRIDE, size_t UV_OFFSET>
78        void apply(const void* vertices) {
79            intptr_t xyPtr = reinterpret_cast<intptr_t>(vertices);
80            intptr_t uvPtr = reinterpret_cast<intptr_t>(vertices) + UV_OFFSET;
81            float sx = fM[0];
82            float kx = fM[1];
83            float tx = fM[2];
84            float ky = fM[3];
85            float sy = fM[4];
86            float ty = fM[5];
87            for (int i = 0; i < N; ++i) {
88                const GrPoint* xy = reinterpret_cast<const GrPoint*>(xyPtr);
89                GrPoint* uv = reinterpret_cast<GrPoint*>(uvPtr);
90                uv->fX = sx * xy->fX + kx * xy->fY + tx;
91                uv->fY = ky * xy->fX + sy * xy->fY + ty;
92                xyPtr += STRIDE;
93                uvPtr += STRIDE;
94            }
95        }
96    private:
97        float fM[6];
98    };
99
100
101    // Converts a cubic into a sequence of quads. If working in device space
102    // use tolScale = 1, otherwise set based on stretchiness of the matrix. The
103    // result is sets of 3 points in quads (TODO: share endpoints in returned
104    // array)
105    // When we approximate a cubic {a,b,c,d} with a quadratic we may have to
106    // ensure that the new control point lies between the lines ab and cd. The
107    // convex path renderer requires this. It starts with a path where all the
108    // control points taken together form a convex polygon. It relies on this
109    // property and the quadratic approximation of cubics step cannot alter it.
110    // Setting constrainWithinTangents to true enforces this property. When this
111    // is true the cubic must be simple and dir must specify the orientation of
112    // the cubic. Otherwise, dir is ignored.
113    void convertCubicToQuads(const GrPoint p[4],
114                             SkScalar tolScale,
115                             bool constrainWithinTangents,
116                             SkPath::Direction dir,
117                             SkTArray<SkPoint, true>* quads);
118};
119#endif
120