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 "src/core/SkGeometry.h" 9#include "src/core/SkQuadClipper.h" 10 11#include <utility> 12 13SkQuadClipper::SkQuadClipper() { 14 fClip.setEmpty(); 15} 16 17void 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 24static 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 43static 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 */ 53bool 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