1 /*
2 * Copyright 2009 The Android Open Source Project
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 #include "SkQuadClipper.h"
9 #include "SkGeometry.h"
10
11 #include <utility>
12
SkQuadClipper()13 SkQuadClipper::SkQuadClipper() {
14 fClip.setEmpty();
15 }
16
setClip(const SkIRect & clip)17 void SkQuadClipper::setClip(const SkIRect& clip) {
18 // conver to scalars, since that's where we'll see the points
19 fClip.set(clip);
20 }
21
22 ///////////////////////////////////////////////////////////////////////////////
23
chopMonoQuadAt(SkScalar c0,SkScalar c1,SkScalar c2,SkScalar target,SkScalar * t)24 static bool chopMonoQuadAt(SkScalar c0, SkScalar c1, SkScalar c2,
25 SkScalar target, SkScalar* t) {
26 /* Solve F(t) = y where F(t) := [0](1-t)^2 + 2[1]t(1-t) + [2]t^2
27 * We solve for t, using quadratic equation, hence we have to rearrange
28 * our cooefficents to look like At^2 + Bt + C
29 */
30 SkScalar A = c0 - c1 - c1 + c2;
31 SkScalar B = 2*(c1 - c0);
32 SkScalar C = c0 - target;
33
34 SkScalar roots[2]; // we only expect one, but make room for 2 for safety
35 int count = SkFindUnitQuadRoots(A, B, C, roots);
36 if (count) {
37 *t = roots[0];
38 return true;
39 }
40 return false;
41 }
42
chopMonoQuadAtY(SkPoint pts[3],SkScalar y,SkScalar * t)43 static bool chopMonoQuadAtY(SkPoint pts[3], SkScalar y, SkScalar* t) {
44 return chopMonoQuadAt(pts[0].fY, pts[1].fY, pts[2].fY, y, t);
45 }
46
47 ///////////////////////////////////////////////////////////////////////////////
48
49 /* If we somehow returned the fact that we had to flip the pts in Y, we could
50 communicate that to setQuadratic, and then avoid having to flip it back
51 here (only to have setQuadratic do the flip again)
52 */
clipQuad(const SkPoint srcPts[3],SkPoint dst[3])53 bool SkQuadClipper::clipQuad(const SkPoint srcPts[3], SkPoint dst[3]) {
54 bool reverse;
55
56 // we need the data to be monotonically increasing in Y
57 if (srcPts[0].fY > srcPts[2].fY) {
58 dst[0] = srcPts[2];
59 dst[1] = srcPts[1];
60 dst[2] = srcPts[0];
61 reverse = true;
62 } else {
63 memcpy(dst, srcPts, 3 * sizeof(SkPoint));
64 reverse = false;
65 }
66
67 // are we completely above or below
68 const SkScalar ctop = fClip.fTop;
69 const SkScalar cbot = fClip.fBottom;
70 if (dst[2].fY <= ctop || dst[0].fY >= cbot) {
71 return false;
72 }
73
74 SkScalar t;
75 SkPoint tmp[5]; // for SkChopQuadAt
76
77 // are we partially above
78 if (dst[0].fY < ctop) {
79 if (chopMonoQuadAtY(dst, ctop, &t)) {
80 // take the 2nd chopped quad
81 SkChopQuadAt(dst, tmp, t);
82 dst[0] = tmp[2];
83 dst[1] = tmp[3];
84 } else {
85 // if chopMonoQuadAtY failed, then we may have hit inexact numerics
86 // so we just clamp against the top
87 for (int i = 0; i < 3; i++) {
88 if (dst[i].fY < ctop) {
89 dst[i].fY = ctop;
90 }
91 }
92 }
93 }
94
95 // are we partially below
96 if (dst[2].fY > cbot) {
97 if (chopMonoQuadAtY(dst, cbot, &t)) {
98 SkChopQuadAt(dst, tmp, t);
99 dst[1] = tmp[1];
100 dst[2] = tmp[2];
101 } else {
102 // if chopMonoQuadAtY failed, then we may have hit inexact numerics
103 // so we just clamp against the bottom
104 for (int i = 0; i < 3; i++) {
105 if (dst[i].fY > cbot) {
106 dst[i].fY = cbot;
107 }
108 }
109 }
110 }
111
112 if (reverse) {
113 using std::swap;
114 swap(dst[0], dst[2]);
115 }
116 return true;
117 }
118