path ops -- rewrite angle sort

This is a major change resulting from a minor
tweak. In the old code, the intersection point
of two curves was shared between them, but the
intersection points and end points of sorted edges was
computed directly from the intersection T value.

In this CL, both intersection points and sorted points
are the same, and intermediate control points are computed
to preserve their slope.

The sort itself has been completely rewritten to be more
robust and remove 'magic' checks, conditions that empirically
worked but couldn't be rationalized.

This CL was triggered by errors generated computing the clips
of SKP files. At this point, all 73M standard tests work and
at least the first troublesome SKPs work.

Review URL: https://codereview.chromium.org/15338003

git-svn-id: http://skia.googlecode.com/svn/trunk@9432 2bbb7eff-a529-9590-31e7-b0007b416f81

1 files changed, 36 insertions, 0 deletions

diff --git a/src/pathops/SkPathOpsCubic.cpp b/src/pathops/SkPathOpsCubic.cpp
index 674213c383..c644a67117 100644
--- a/src/pathops/SkPathOpsCubic.cpp
+++ b/src/pathops/SkPathOpsCubic.cpp
@@ -403,11 +403,23 @@ SkDCubic SkDCubic::subDivide(double t1, double t2) const {
     /* by = */ dst[1].fY = (my * 2 - ny) / 18;
     /* cx = */ dst[2].fX = (nx * 2 - mx) / 18;
     /* cy = */ dst[2].fY = (ny * 2 - my) / 18;
+    // FIXME: call align() ?
     return dst;
 }
 
+void SkDCubic::align(int endIndex, int ctrlIndex, SkDPoint* dstPt) const {  
+    if (fPts[endIndex].fX == fPts[ctrlIndex].fX) {
+        dstPt->fX = fPts[endIndex].fX;
+    }
+    if (fPts[endIndex].fY == fPts[ctrlIndex].fY) {
+        dstPt->fY = fPts[endIndex].fY;
+    }
+}
+
 void SkDCubic::subDivide(const SkDPoint& a, const SkDPoint& d,
                          double t1, double t2, SkDPoint dst[2]) const {
+    SkASSERT(t1 != t2);
+#if 0
     double ex = interp_cubic_coords(&fPts[0].fX, (t1 * 2 + t2) / 3);
     double ey = interp_cubic_coords(&fPts[0].fY, (t1 * 2 + t2) / 3);
     double fx = interp_cubic_coords(&fPts[0].fX, (t1 + t2 * 2) / 3);
@@ -420,6 +432,30 @@ void SkDCubic::subDivide(const SkDPoint& a, const SkDPoint& d,
     /* by = */ dst[0].fY = (my * 2 - ny) / 18;
     /* cx = */ dst[1].fX = (nx * 2 - mx) / 18;
     /* cy = */ dst[1].fY = (ny * 2 - my) / 18;
+#else
+    // this approach assumes that the control points computed directly are accurate enough
+    SkDCubic sub = subDivide(t1, t2);
+    dst[0] = sub[1] + (a - sub[0]);
+    dst[1] = sub[2] + (d - sub[3]);
+#endif
+    if (t1 == 0 || t2 == 0) {
+        align(0, 1, t1 == 0 ? &dst[0] : &dst[1]);
+    }
+    if (t1 == 1 || t2 == 1) {
+        align(3, 2, t1 == 1 ? &dst[0] : &dst[1]);
+    }
+    if (precisely_subdivide_equal(dst[0].fX, a.fX)) {
+        dst[0].fX = a.fX;
+    }
+    if (precisely_subdivide_equal(dst[0].fY, a.fY)) {
+        dst[0].fY = a.fY;
+    }
+    if (precisely_subdivide_equal(dst[1].fX, d.fX)) {
+        dst[1].fX = d.fX;
+    }
+    if (precisely_subdivide_equal(dst[1].fY, d.fY)) {
+        dst[1].fY = d.fY;
+    }
 }
 
 /* classic one t subdivision */