1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/gfx/skia/trunk/src/core/SkQuadClipper.cpp Wed Dec 31 06:09:35 2014 +0100
1.3 @@ -0,0 +1,114 @@
1.4 +/*
1.5 + * Copyright 2009 The Android Open Source Project
1.6 + *
1.7 + * Use of this source code is governed by a BSD-style license that can be
1.8 + * found in the LICENSE file.
1.9 + */
1.10 +
1.11 +#include "SkQuadClipper.h"
1.12 +#include "SkGeometry.h"
1.13 +
1.14 +SkQuadClipper::SkQuadClipper() {
1.15 + fClip.setEmpty();
1.16 +}
1.17 +
1.18 +void SkQuadClipper::setClip(const SkIRect& clip) {
1.19 + // conver to scalars, since that's where we'll see the points
1.20 + fClip.set(clip);
1.21 +}
1.22 +
1.23 +///////////////////////////////////////////////////////////////////////////////
1.24 +
1.25 +static bool chopMonoQuadAt(SkScalar c0, SkScalar c1, SkScalar c2,
1.26 + SkScalar target, SkScalar* t) {
1.27 + /* Solve F(t) = y where F(t) := [0](1-t)^2 + 2[1]t(1-t) + [2]t^2
1.28 + * We solve for t, using quadratic equation, hence we have to rearrange
1.29 + * our cooefficents to look like At^2 + Bt + C
1.30 + */
1.31 + SkScalar A = c0 - c1 - c1 + c2;
1.32 + SkScalar B = 2*(c1 - c0);
1.33 + SkScalar C = c0 - target;
1.34 +
1.35 + SkScalar roots[2]; // we only expect one, but make room for 2 for safety
1.36 + int count = SkFindUnitQuadRoots(A, B, C, roots);
1.37 + if (count) {
1.38 + *t = roots[0];
1.39 + return true;
1.40 + }
1.41 + return false;
1.42 +}
1.43 +
1.44 +static bool chopMonoQuadAtY(SkPoint pts[3], SkScalar y, SkScalar* t) {
1.45 + return chopMonoQuadAt(pts[0].fY, pts[1].fY, pts[2].fY, y, t);
1.46 +}
1.47 +
1.48 +///////////////////////////////////////////////////////////////////////////////
1.49 +
1.50 +/* If we somehow returned the fact that we had to flip the pts in Y, we could
1.51 + communicate that to setQuadratic, and then avoid having to flip it back
1.52 + here (only to have setQuadratic do the flip again)
1.53 + */
1.54 +bool SkQuadClipper::clipQuad(const SkPoint srcPts[3], SkPoint dst[3]) {
1.55 + bool reverse;
1.56 +
1.57 + // we need the data to be monotonically increasing in Y
1.58 + if (srcPts[0].fY > srcPts[2].fY) {
1.59 + dst[0] = srcPts[2];
1.60 + dst[1] = srcPts[1];
1.61 + dst[2] = srcPts[0];
1.62 + reverse = true;
1.63 + } else {
1.64 + memcpy(dst, srcPts, 3 * sizeof(SkPoint));
1.65 + reverse = false;
1.66 + }
1.67 +
1.68 + // are we completely above or below
1.69 + const SkScalar ctop = fClip.fTop;
1.70 + const SkScalar cbot = fClip.fBottom;
1.71 + if (dst[2].fY <= ctop || dst[0].fY >= cbot) {
1.72 + return false;
1.73 + }
1.74 +
1.75 + SkScalar t;
1.76 + SkPoint tmp[5]; // for SkChopQuadAt
1.77 +
1.78 + // are we partially above
1.79 + if (dst[0].fY < ctop) {
1.80 + if (chopMonoQuadAtY(dst, ctop, &t)) {
1.81 + // take the 2nd chopped quad
1.82 + SkChopQuadAt(dst, tmp, t);
1.83 + dst[0] = tmp[2];
1.84 + dst[1] = tmp[3];
1.85 + } else {
1.86 + // if chopMonoQuadAtY failed, then we may have hit inexact numerics
1.87 + // so we just clamp against the top
1.88 + for (int i = 0; i < 3; i++) {
1.89 + if (dst[i].fY < ctop) {
1.90 + dst[i].fY = ctop;
1.91 + }
1.92 + }
1.93 + }
1.94 + }
1.95 +
1.96 + // are we partially below
1.97 + if (dst[2].fY > cbot) {
1.98 + if (chopMonoQuadAtY(dst, cbot, &t)) {
1.99 + SkChopQuadAt(dst, tmp, t);
1.100 + dst[1] = tmp[1];
1.101 + dst[2] = tmp[2];
1.102 + } else {
1.103 + // if chopMonoQuadAtY failed, then we may have hit inexact numerics
1.104 + // so we just clamp against the bottom
1.105 + for (int i = 0; i < 3; i++) {
1.106 + if (dst[i].fY > cbot) {
1.107 + dst[i].fY = cbot;
1.108 + }
1.109 + }
1.110 + }
1.111 + }
1.112 +
1.113 + if (reverse) {
1.114 + SkTSwap<SkPoint>(dst[0], dst[2]);
1.115 + }
1.116 + return true;
1.117 +}
