1 /*
2 * Copyright (C) 2009 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 #include "SkQuadClipper.h"
18 #include "SkGeometry.h"
19
clamp_le(SkScalar & value,SkScalar max)20 static inline void clamp_le(SkScalar& value, SkScalar max) {
21 if (value > max) {
22 value = max;
23 }
24 }
25
clamp_ge(SkScalar & value,SkScalar min)26 static inline void clamp_ge(SkScalar& value, SkScalar min) {
27 if (value < min) {
28 value = min;
29 }
30 }
31
SkQuadClipper()32 SkQuadClipper::SkQuadClipper() {}
33
setClip(const SkIRect & clip)34 void SkQuadClipper::setClip(const SkIRect& clip) {
35 // conver to scalars, since that's where we'll see the points
36 fClip.set(clip);
37 }
38
39 ///////////////////////////////////////////////////////////////////////////////
40
chopMonoQuadAt(SkScalar c0,SkScalar c1,SkScalar c2,SkScalar target,SkScalar * t)41 static bool chopMonoQuadAt(SkScalar c0, SkScalar c1, SkScalar c2,
42 SkScalar target, SkScalar* t) {
43 /* Solve F(t) = y where F(t) := [0](1-t)^2 + 2[1]t(1-t) + [2]t^2
44 * We solve for t, using quadratic equation, hence we have to rearrange
45 * our cooefficents to look like At^2 + Bt + C
46 */
47 SkScalar A = c0 - c1 - c1 + c2;
48 SkScalar B = 2*(c1 - c0);
49 SkScalar C = c0 - target;
50
51 SkScalar roots[2]; // we only expect one, but make room for 2 for safety
52 int count = SkFindUnitQuadRoots(A, B, C, roots);
53 if (count) {
54 *t = roots[0];
55 return true;
56 }
57 return false;
58 }
59
chopMonoQuadAtY(SkPoint pts[3],SkScalar y,SkScalar * t)60 static bool chopMonoQuadAtY(SkPoint pts[3], SkScalar y, SkScalar* t) {
61 return chopMonoQuadAt(pts[0].fY, pts[1].fY, pts[2].fY, y, t);
62 }
63
64 ///////////////////////////////////////////////////////////////////////////////
65
66 /* If we somehow returned the fact that we had to flip the pts in Y, we could
67 communicate that to setQuadratic, and then avoid having to flip it back
68 here (only to have setQuadratic do the flip again)
69 */
clipQuad(const SkPoint srcPts[3],SkPoint dst[3])70 bool SkQuadClipper::clipQuad(const SkPoint srcPts[3], SkPoint dst[3]) {
71 bool reverse;
72
73 // we need the data to be monotonically increasing in Y
74 if (srcPts[0].fY > srcPts[2].fY) {
75 dst[0] = srcPts[2];
76 dst[1] = srcPts[1];
77 dst[2] = srcPts[0];
78 reverse = true;
79 } else {
80 memcpy(dst, srcPts, 3 * sizeof(SkPoint));
81 reverse = false;
82 }
83
84 // are we completely above or below
85 const SkScalar ctop = fClip.fTop;
86 const SkScalar cbot = fClip.fBottom;
87 if (dst[2].fY <= ctop || dst[0].fY >= cbot) {
88 return false;
89 }
90
91 SkScalar t;
92 SkPoint tmp[5]; // for SkChopQuadAt
93
94 // are we partially above
95 if (dst[0].fY < ctop) {
96 if (chopMonoQuadAtY(dst, ctop, &t)) {
97 // take the 2nd chopped quad
98 SkChopQuadAt(dst, tmp, t);
99 dst[0] = tmp[2];
100 dst[1] = tmp[3];
101 } else {
102 // if chopMonoQuadAtY failed, then we may have hit inexact numerics
103 // so we just clamp against the top
104 for (int i = 0; i < 3; i++) {
105 if (dst[i].fY < ctop) {
106 dst[i].fY = ctop;
107 }
108 }
109 }
110 }
111
112 // are we partially below
113 if (dst[2].fY > cbot) {
114 if (chopMonoQuadAtY(dst, cbot, &t)) {
115 SkChopQuadAt(dst, tmp, t);
116 dst[1] = tmp[1];
117 dst[2] = tmp[2];
118 } else {
119 // if chopMonoQuadAtY failed, then we may have hit inexact numerics
120 // so we just clamp against the bottom
121 for (int i = 0; i < 3; i++) {
122 if (dst[i].fY > cbot) {
123 dst[i].fY = cbot;
124 }
125 }
126 }
127 }
128
129 if (reverse) {
130 SkTSwap<SkPoint>(dst[0], dst[2]);
131 }
132 return true;
133 }
134
135