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