tree cc8e217642726cc6fe8fd37626dff0a95212b83d
parent 5eb29448dfbdf832d36d9e3c3151c229dfb59cb9
author Cary Clark <caryclark@skia.org> 1544644223 -0500
committer Skia Commit-Bot <skia-commit-bot@chromium.org> 1544706284 +0000

two pass convexity

This separates the existing convexity logic into
two passes. The first pass detects concavity by
counting the changes in direction.
The second pass computes the cross product to
see that all angles bend in the same direction, and
computes the dot product to see if the angle
doubles back on itself.

The second pass treats axis-aligned vectors
separately, and computes the dot and cross products
by comparing point values; it does not use arithmetic
to determine convexity, so it works with all finite
values.

A compile time switch enables returning concave
for co-linear diagonal points:
If successive points are not axis-aligned, and
those points are co-linear along a diagonal;
the path is treated as concave. This is conservative
but avoids paths that change convexity when the
are translated or scaled, since transforming the
path may cause the midpoint to shift to either
side of a line formed by the endpoints.

The compile time switch is set so that co-linear
diagonal points do not affect convexity. Note that
this permits shapes formerly considered concave, such
as stroked lines with round caps, to become convex;
this accounts for many of the GM differences.

A path may double back on itself and be convex;
for instance, a path containing a single line.

Path may have multiple initial moveTo verbs, or
trailing moveTo verbs, and still evaluate as convex.

A separate entry point, SkPathPriv::IsConvex()
allows passing an array of points instead of a path.

A legacy define has been checked into Chrome to
use the old code until layout tests have been
rebaselined.

R=reed@google.com,bsalomon@google.com
Bug:899689
Change-Id: I392bbe04836ffb19666ad92ab2a2404c56543019
Reviewed-on: https://skia-review.googlesource.com/c/173427
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Cary Clark <caryclark@google.com>
Commit-Queue: Cary Clark <caryclark@skia.org>