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Fix infinite recursion in cubic->quad conversion, also attempt to detect nearly flat cubics early.

Browse Source 
Review URL: http://codereview.appspot.com/6448100/

THIS WILL REQUIRE REBASELINING OF CONVEXPATHS GM.



git-svn-id: http://skia.googlecode.com/svn/trunk@4917 2bbb7eff-a529-9590-31e7-b0007b416f81
This commit is contained in:
bsalomon@google.com 2012-08-02 14:55:45 +00:00
parent c8d640b178
commit 54ad851361
2 changed files with 87 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

45
gm/convexpaths.cpp
View File

@ -40,7 +40,7 @@ protected:
virtual SkISize onISize() {
return make_isize(1200, 900);
return make_isize(1200, 1100);
}
void makePaths() {
@ -48,7 +48,6 @@ protected:
return;
}
fOnce.accomplished();
// CW
fPaths.push_back().moveTo(0, 0);
fPaths.back().quadTo(50 * SK_Scalar1, 100 * SK_Scalar1,
@ -126,14 +125,14 @@ protected:
fPaths.back().lineTo(98 * SK_Scalar1, 100 * SK_Scalar1);
fPaths.back().lineTo(3 * SK_Scalar1, 96 * SK_Scalar1);
/*
It turns out arcTos are not automatically marked as convex and they
may in fact be ever so slightly concave.
fPaths.push_back().arcTo(SkRect::MakeXYWH(0, 0,
50 * SK_Scalar1,
100 * SK_Scalar1),
25 * SK_Scalar1, 130 * SK_Scalar1, false);
*/
//It turns out arcTos are not automatically marked as convex and they
//may in fact be ever so slightly concave.
//fPaths.push_back().arcTo(SkRect::MakeXYWH(0, 0,
// 50 * SK_Scalar1,
// 100 * SK_Scalar1),
// 25 * SK_Scalar1, 130 * SK_Scalar1, false);
// cubics
fPaths.push_back().cubicTo( 1 * SK_Scalar1, 1 * SK_Scalar1,
10 * SK_Scalar1, 90 * SK_Scalar1,
@ -141,7 +140,7 @@ protected:
fPaths.push_back().cubicTo(100 * SK_Scalar1, 50 * SK_Scalar1,
20 * SK_Scalar1, 100 * SK_Scalar1,
0 * SK_Scalar1, 0 * SK_Scalar1);
// path that has a cubic with a repeated first control point and
// a repeated last control point.
fPaths.push_back().moveTo(SK_Scalar1 * 10, SK_Scalar1 * 10);
@ -163,6 +162,30 @@ protected:
50 * SK_Scalar1, 0,
50 * SK_Scalar1, 10 * SK_Scalar1);
// cubic where last three points are almost a line
fPaths.push_back().moveTo(0, 228 * SK_Scalar1 / 8);
fPaths.back().cubicTo(628 * SK_Scalar1 / 8, 82 * SK_Scalar1 / 8,
1255 * SK_Scalar1 / 8, 141 * SK_Scalar1 / 8,
1883 * SK_Scalar1 / 8, 202 * SK_Scalar1 / 8);
// flat cubic where the at end point tangents both point outward.
fPaths.push_back().moveTo(10 * SK_Scalar1, 0);
fPaths.back().cubicTo(0, SK_Scalar1,
30 * SK_Scalar1, SK_Scalar1,
20 * SK_Scalar1, 0);
// flat cubic where initial tangent is in, end tangent out
fPaths.push_back().moveTo(0, 0 * SK_Scalar1);
fPaths.back().cubicTo(10 * SK_Scalar1, SK_Scalar1,
30 * SK_Scalar1, SK_Scalar1,
20 * SK_Scalar1, 0);
// flat cubic where initial tangent is out, end tangent in
fPaths.push_back().moveTo(10 * SK_Scalar1, 0);
fPaths.back().cubicTo(0, SK_Scalar1,
20 * SK_Scalar1, SK_Scalar1,
30 * SK_Scalar1, 0);
// triangle where one edge is a degenerate quad
fPaths.push_back().moveTo(SkFloatToScalar(8.59375f), 45 * SK_Scalar1);
fPaths.back().quadTo(SkFloatToScalar(16.9921875f), 45 * SK_Scalar1,

59
src/gpu/GrPathUtils.cpp
View File

@ -324,6 +324,10 @@ void convert_noninflect_cubic_to_quads(const SkPoint p[4],
SkPath::Direction dir,
SkTArray<SkPoint, true>* quads,
int sublevel = 0) {
// Notation: Point a is always p[0]. Point b is p[1] unless p[1] == p[0], in which case it is
// p[2]. Point d is always p[3]. Point c is p[2] unless p[2] == p[3], in which case it is p[1].
SkVector ab = p[1] - p[0];
SkVector dc = p[2] - p[3];
@ -341,6 +345,51 @@ void convert_noninflect_cubic_to_quads(const SkPoint p[4],
dc = p[1] - p[3];
}
// When the ab and cd tangents are nearly parallel with vector from d to a the constraint that
// the quad point falls between the tangents becomes hard to enforce and we are likely to hit
// the max subdivision count. However, in this case the cubic is approaching a line and the
// accuracy of the quad point isn't so important. We check if the two middle cubic control
// points are very close to the baseline vector. If so then we just pick quadratic points on the
// control polygon.
if (constrainWithinTangents) {
SkVector da = p[0] - p[3];
SkScalar invDALengthSqd = da.lengthSqd();
if (invDALengthSqd > SK_ScalarNearlyZero) {
invDALengthSqd = SkScalarInvert(invDALengthSqd);
// cross(ab, da)^2/length(da)^2 == sqd distance from b to line from d to a.
// same goed for point c using vector cd.
SkScalar detABSqd = ab.cross(da);
detABSqd = SkScalarSquare(detABSqd);
SkScalar detDCSqd = dc.cross(da);
detDCSqd = SkScalarSquare(detDCSqd);
if (SkScalarMul(detABSqd, invDALengthSqd) < toleranceSqd &&
SkScalarMul(detDCSqd, invDALengthSqd) < toleranceSqd) {
SkPoint b = p[0] + ab;
SkPoint c = p[3] + dc;
SkPoint mid = b + c;
mid.scale(SK_ScalarHalf);
// Insert two quadratics to cover the case when ab points away from d and/or dc
// points away from a.
if (SkVector::DotProduct(da, dc) < 0 || SkVector::DotProduct(ab,da) > 0) {
SkPoint* qpts = quads->push_back_n(6);
qpts[0] = p[0];
qpts[1] = b;
qpts[2] = mid;
qpts[3] = mid;
qpts[4] = c;
qpts[5] = p[3];
} else {
SkPoint* qpts = quads->push_back_n(3);
qpts[0] = p[0];
qpts[1] = mid;
qpts[2] = p[3];
}
return;
}
}
}
static const SkScalar kLengthScale = 3 * SK_Scalar1 / 2;
static const int kMaxSubdivs = 10;
@ -353,7 +402,7 @@ void convert_noninflect_cubic_to_quads(const SkPoint p[4],
SkVector c1 = p[3];
c1 += dc;
SkScalar dSqd = sublevel > kMaxSubdivs ? toleranceSqd : c0.distanceToSqd(c1);
SkScalar dSqd = sublevel > kMaxSubdivs ? 0 : c0.distanceToSqd(c1);
if (dSqd < toleranceSqd) {
SkPoint cAvg = c0;
cAvg += c1;
@ -363,8 +412,7 @@ void convert_noninflect_cubic_to_quads(const SkPoint p[4],
if (constrainWithinTangents &&
!is_point_within_cubic_tangents(p[0], ab, dc, p[3], dir, cAvg)) {
// choose a new cAvg that is the intersection of the two tangent
// lines.
// choose a new cAvg that is the intersection of the two tangent lines.
ab.setOrthog(ab);
SkScalar z0 = -ab.dot(p[0]);
dc.setOrthog(dc);
@ -378,9 +426,8 @@ void convert_noninflect_cubic_to_quads(const SkPoint p[4],
if (sublevel <= kMaxSubdivs) {
SkScalar d0Sqd = c0.distanceToSqd(cAvg);
SkScalar d1Sqd = c1.distanceToSqd(cAvg);
// We need to subdivide if d0 + d1 > tolerance but we have the
// sqd values. We know the distances and tolerance can't be
// negative.
// We need to subdivide if d0 + d1 > tolerance but we have the sqd values. We know
// the distances and tolerance can't be negative.
// (d0 + d1)^2 > toleranceSqd
// d0Sqd + 2*d0*d1 + d1Sqd > toleranceSqd
SkScalar d0d1 = SkScalarSqrt(SkScalarMul(d0Sqd, d1Sqd));