| /* |
| * Copyright 2009 The Android Open Source Project |
| * |
| * Use of this source code is governed by a BSD-style license that can be |
| * found in the LICENSE file. |
| */ |
| |
| #include "SkQuadClipper.h" |
| #include "SkGeometry.h" |
| |
| SkQuadClipper::SkQuadClipper() { |
| fClip.setEmpty(); |
| } |
| |
| void SkQuadClipper::setClip(const SkIRect& clip) { |
| // conver to scalars, since that's where we'll see the points |
| fClip.set(clip); |
| } |
| |
| /////////////////////////////////////////////////////////////////////////////// |
| |
| static bool chopMonoQuadAt(SkScalar c0, SkScalar c1, SkScalar c2, |
| SkScalar target, SkScalar* t) { |
| /* Solve F(t) = y where F(t) := [0](1-t)^2 + 2[1]t(1-t) + [2]t^2 |
| * We solve for t, using quadratic equation, hence we have to rearrange |
| * our cooefficents to look like At^2 + Bt + C |
| */ |
| SkScalar A = c0 - c1 - c1 + c2; |
| SkScalar B = 2*(c1 - c0); |
| SkScalar C = c0 - target; |
| |
| SkScalar roots[2]; // we only expect one, but make room for 2 for safety |
| int count = SkFindUnitQuadRoots(A, B, C, roots); |
| if (count) { |
| *t = roots[0]; |
| return true; |
| } |
| return false; |
| } |
| |
| static bool chopMonoQuadAtY(SkPoint pts[3], SkScalar y, SkScalar* t) { |
| return chopMonoQuadAt(pts[0].fY, pts[1].fY, pts[2].fY, y, t); |
| } |
| |
| /////////////////////////////////////////////////////////////////////////////// |
| |
| /* If we somehow returned the fact that we had to flip the pts in Y, we could |
| communicate that to setQuadratic, and then avoid having to flip it back |
| here (only to have setQuadratic do the flip again) |
| */ |
| bool SkQuadClipper::clipQuad(const SkPoint srcPts[3], SkPoint dst[3]) { |
| bool reverse; |
| |
| // we need the data to be monotonically increasing in Y |
| if (srcPts[0].fY > srcPts[2].fY) { |
| dst[0] = srcPts[2]; |
| dst[1] = srcPts[1]; |
| dst[2] = srcPts[0]; |
| reverse = true; |
| } else { |
| memcpy(dst, srcPts, 3 * sizeof(SkPoint)); |
| reverse = false; |
| } |
| |
| // are we completely above or below |
| const SkScalar ctop = fClip.fTop; |
| const SkScalar cbot = fClip.fBottom; |
| if (dst[2].fY <= ctop || dst[0].fY >= cbot) { |
| return false; |
| } |
| |
| SkScalar t; |
| SkPoint tmp[5]; // for SkChopQuadAt |
| |
| // are we partially above |
| if (dst[0].fY < ctop) { |
| if (chopMonoQuadAtY(dst, ctop, &t)) { |
| // take the 2nd chopped quad |
| SkChopQuadAt(dst, tmp, t); |
| dst[0] = tmp[2]; |
| dst[1] = tmp[3]; |
| } else { |
| // if chopMonoQuadAtY failed, then we may have hit inexact numerics |
| // so we just clamp against the top |
| for (int i = 0; i < 3; i++) { |
| if (dst[i].fY < ctop) { |
| dst[i].fY = ctop; |
| } |
| } |
| } |
| } |
| |
| // are we partially below |
| if (dst[2].fY > cbot) { |
| if (chopMonoQuadAtY(dst, cbot, &t)) { |
| SkChopQuadAt(dst, tmp, t); |
| dst[1] = tmp[1]; |
| dst[2] = tmp[2]; |
| } else { |
| // if chopMonoQuadAtY failed, then we may have hit inexact numerics |
| // so we just clamp against the bottom |
| for (int i = 0; i < 3; i++) { |
| if (dst[i].fY > cbot) { |
| dst[i].fY = cbot; |
| } |
| } |
| } |
| } |
| |
| if (reverse) { |
| SkTSwap<SkPoint>(dst[0], dst[2]); |
| } |
| return true; |
| } |