diff options
author | caryclark <caryclark@google.com> | 2015-08-25 08:03:01 -0700 |
---|---|---|
committer | Commit bot <commit-bot@chromium.org> | 2015-08-25 08:03:01 -0700 |
commit | 7544124fb8ee744f68f549a353f8a9163cd7432d (patch) | |
tree | 05b3c0bde241520b07e9caa86045542d72b1dc88 /src/core/SkGeometry.cpp | |
parent | cf72ed6a3eb13d0ed1aa45beb984bafafa7afff3 (diff) |
fix zero-length tangent
If the end point and the control point are the same, computing
the tangent will result in (0, 0). In this case, use the prior
control point instead.
R=reed@google.com
BUG=skia:4191
Review URL: https://codereview.chromium.org/1311273002
Diffstat (limited to 'src/core/SkGeometry.cpp')
-rw-r--r-- | src/core/SkGeometry.cpp | 49 |
1 files changed, 30 insertions, 19 deletions
diff --git a/src/core/SkGeometry.cpp b/src/core/SkGeometry.cpp index 6afd9d7ffb..7462009479 100644 --- a/src/core/SkGeometry.cpp +++ b/src/core/SkGeometry.cpp @@ -130,13 +130,6 @@ static SkScalar eval_quad(const SkScalar src[], SkScalar t) { #endif } -static SkScalar eval_quad_derivative(const SkScalar src[], SkScalar t) { - SkScalar A = src[4] - 2 * src[2] + src[0]; - SkScalar B = src[2] - src[0]; - - return 2 * SkScalarMulAdd(A, t, B); -} - void SkQuadToCoeff(const SkPoint pts[3], SkPoint coeff[3]) { Sk2s p0 = from_point(pts[0]); Sk2s p1 = from_point(pts[1]); @@ -157,8 +150,7 @@ void SkEvalQuadAt(const SkPoint src[3], SkScalar t, SkPoint* pt, SkVector* tange pt->set(eval_quad(&src[0].fX, t), eval_quad(&src[0].fY, t)); } if (tangent) { - tangent->set(eval_quad_derivative(&src[0].fX, t), - eval_quad_derivative(&src[0].fY, t)); + *tangent = SkEvalQuadTangentAt(src, t); } } @@ -179,6 +171,12 @@ SkPoint SkEvalQuadAt(const SkPoint src[3], SkScalar t) { } SkVector SkEvalQuadTangentAt(const SkPoint src[3], SkScalar t) { + // The derivative equation is 2(b - a +(a - 2b +c)t). This returns a + // zero tangent vector when t is 0 or 1, and the control point is equal + // to the end point. In this case, use the quad end points to compute the tangent. + if ((t == 0 && src[0] == src[1]) || (t == 1 && src[1] == src[2])) { + return src[2] - src[0]; + } SkASSERT(src); SkASSERT(t >= 0 && t <= SK_Scalar1); @@ -398,8 +396,22 @@ void SkEvalCubicAt(const SkPoint src[4], SkScalar t, SkPoint* loc, loc->set(eval_cubic(&src[0].fX, t), eval_cubic(&src[0].fY, t)); } if (tangent) { - tangent->set(eval_cubic_derivative(&src[0].fX, t), - eval_cubic_derivative(&src[0].fY, t)); + // The derivative equation returns a zero tangent vector when t is 0 or 1, and the + // adjacent control point is equal to the end point. In this case, use the + // next control point or the end points to compute the tangent. + if ((t == 0 && src[0] == src[1]) || (t == 1 && src[2] == src[3])) { + if (t == 0) { + *tangent = src[2] - src[0]; + } else { + *tangent = src[3] - src[1]; + } + if (!tangent->fX && !tangent->fY) { + *tangent = src[3] - src[0]; + } + } else { + tangent->set(eval_cubic_derivative(&src[0].fX, t), + eval_cubic_derivative(&src[0].fY, t)); + } } if (curvature) { curvature->set(eval_cubic_2ndDerivative(&src[0].fX, t), @@ -1176,12 +1188,6 @@ static void conic_deriv_coeff(const SkScalar src[], coeff[2] = wP10; } -static SkScalar conic_eval_tan(const SkScalar coord[], SkScalar w, SkScalar t) { - SkScalar coeff[3]; - conic_deriv_coeff(coord, w, coeff); - return t * (t * coeff[0] + coeff[1]) + coeff[2]; -} - static bool conic_find_extrema(const SkScalar src[], SkScalar w, SkScalar* t) { SkScalar coeff[3]; conic_deriv_coeff(src, w, coeff); @@ -1232,8 +1238,7 @@ void SkConic::evalAt(SkScalar t, SkPoint* pt, SkVector* tangent) const { conic_eval_pos(&fPts[0].fY, fW, t)); } if (tangent) { - tangent->set(conic_eval_tan(&fPts[0].fX, fW, t), - conic_eval_tan(&fPts[0].fY, fW, t)); + *tangent = evalTangentAt(t); } } @@ -1291,6 +1296,12 @@ SkPoint SkConic::evalAt(SkScalar t) const { } SkVector SkConic::evalTangentAt(SkScalar t) const { + // The derivative equation returns a zero tangent vector when t is 0 or 1, + // and the control point is equal to the end point. + // In this case, use the conic endpoints to compute the tangent. + if ((t == 0 && fPts[0] == fPts[1]) || (t == 1 && fPts[1] == fPts[2])) { + return fPts[2] - fPts[0]; + } Sk2s p0 = from_point(fPts[0]); Sk2s p1 = from_point(fPts[1]); Sk2s p2 = from_point(fPts[2]); |