1
2 /*
3 * Copyright 2009 The Android Open Source Project
4 *
5 * Use of this source code is governed by a BSD-style license that can be
6 * found in the LICENSE file.
7 */
8
9
10 #include "SkQuadClipper.h"
11 #include "SkGeometry.h"
12
clamp_le(SkScalar & value,SkScalar max)13 static inline void clamp_le(SkScalar& value, SkScalar max) {
14 if (value > max) {
15 value = max;
16 }
17 }
18
clamp_ge(SkScalar & value,SkScalar min)19 static inline void clamp_ge(SkScalar& value, SkScalar min) {
20 if (value < min) {
21 value = min;
22 }
23 }
24
SkQuadClipper()25 SkQuadClipper::SkQuadClipper() {}
26
setClip(const SkIRect & clip)27 void SkQuadClipper::setClip(const SkIRect& clip) {
28 // conver to scalars, since that's where we'll see the points
29 fClip.set(clip);
30 }
31
32 ///////////////////////////////////////////////////////////////////////////////
33
chopMonoQuadAt(SkScalar c0,SkScalar c1,SkScalar c2,SkScalar target,SkScalar * t)34 static bool chopMonoQuadAt(SkScalar c0, SkScalar c1, SkScalar c2,
35 SkScalar target, SkScalar* t) {
36 /* Solve F(t) = y where F(t) := [0](1-t)^2 + 2[1]t(1-t) + [2]t^2
37 * We solve for t, using quadratic equation, hence we have to rearrange
38 * our cooefficents to look like At^2 + Bt + C
39 */
40 SkScalar A = c0 - c1 - c1 + c2;
41 SkScalar B = 2*(c1 - c0);
42 SkScalar C = c0 - target;
43
44 SkScalar roots[2]; // we only expect one, but make room for 2 for safety
45 int count = SkFindUnitQuadRoots(A, B, C, roots);
46 if (count) {
47 *t = roots[0];
48 return true;
49 }
50 return false;
51 }
52
chopMonoQuadAtY(SkPoint pts[3],SkScalar y,SkScalar * t)53 static bool chopMonoQuadAtY(SkPoint pts[3], SkScalar y, SkScalar* t) {
54 return chopMonoQuadAt(pts[0].fY, pts[1].fY, pts[2].fY, y, t);
55 }
56
57 ///////////////////////////////////////////////////////////////////////////////
58
59 /* If we somehow returned the fact that we had to flip the pts in Y, we could
60 communicate that to setQuadratic, and then avoid having to flip it back
61 here (only to have setQuadratic do the flip again)
62 */
clipQuad(const SkPoint srcPts[3],SkPoint dst[3])63 bool SkQuadClipper::clipQuad(const SkPoint srcPts[3], SkPoint dst[3]) {
64 bool reverse;
65
66 // we need the data to be monotonically increasing in Y
67 if (srcPts[0].fY > srcPts[2].fY) {
68 dst[0] = srcPts[2];
69 dst[1] = srcPts[1];
70 dst[2] = srcPts[0];
71 reverse = true;
72 } else {
73 memcpy(dst, srcPts, 3 * sizeof(SkPoint));
74 reverse = false;
75 }
76
77 // are we completely above or below
78 const SkScalar ctop = fClip.fTop;
79 const SkScalar cbot = fClip.fBottom;
80 if (dst[2].fY <= ctop || dst[0].fY >= cbot) {
81 return false;
82 }
83
84 SkScalar t;
85 SkPoint tmp[5]; // for SkChopQuadAt
86
87 // are we partially above
88 if (dst[0].fY < ctop) {
89 if (chopMonoQuadAtY(dst, ctop, &t)) {
90 // take the 2nd chopped quad
91 SkChopQuadAt(dst, tmp, t);
92 dst[0] = tmp[2];
93 dst[1] = tmp[3];
94 } else {
95 // if chopMonoQuadAtY failed, then we may have hit inexact numerics
96 // so we just clamp against the top
97 for (int i = 0; i < 3; i++) {
98 if (dst[i].fY < ctop) {
99 dst[i].fY = ctop;
100 }
101 }
102 }
103 }
104
105 // are we partially below
106 if (dst[2].fY > cbot) {
107 if (chopMonoQuadAtY(dst, cbot, &t)) {
108 SkChopQuadAt(dst, tmp, t);
109 dst[1] = tmp[1];
110 dst[2] = tmp[2];
111 } else {
112 // if chopMonoQuadAtY failed, then we may have hit inexact numerics
113 // so we just clamp against the bottom
114 for (int i = 0; i < 3; i++) {
115 if (dst[i].fY > cbot) {
116 dst[i].fY = cbot;
117 }
118 }
119 }
120 }
121
122 if (reverse) {
123 SkTSwap<SkPoint>(dst[0], dst[2]);
124 }
125 return true;
126 }
127
128