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 SkQuadClipper::SkQuadClipper() { 12 fClip.setEmpty(); 13 } 14 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 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 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 */ 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
