add interp path

Add path methods to determine if a pair of paths
can be interpolated, and to interpolate them.

R=reed@google.com, robertphillips@google.com
BUG=skia:4549
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1703943003

Review URL: https://codereview.chromium.org/1703943003

1 files changed, 21 insertions, 0 deletions

diff --git a/include/core/SkPath.h b/include/core/SkPath.h
index 9fd7d983cf..6d01f8d162 100644
--- a/include/core/SkPath.h
+++ b/include/core/SkPath.h
@@ -37,6 +37,27 @@ public:
         return !(a == b);
     }
 
+    /** Return true if the paths contain an equal array of verbs and weights. Paths
+     *  with equal verb counts can be readily interpolated. If the paths contain one
+     *  or more conics, the conics' weights must also match.
+     *
+     *  @param compare  The path to compare.
+     *
+     *  @return true if the paths have the same verbs and weights.
+     */
+    bool isInterpolatable(const SkPath& compare) const;
+
+    /** Interpolate between two paths with same-sized point arrays.
+     *  The out path contains the verbs and weights of this path.
+     *  The out points are a weighted average of this path and the ending path. 
+     *
+     *  @param ending  The path to interpolate between.
+     *  @param weight  The weight, from 0 to 1. The output points are set to
+     *                 (this->points * weight) + ending->points * (1 - weight).
+     *  @return true if the paths could be interpolated.
+     */
+    bool interpolate(const SkPath& ending, SkScalar weight, SkPath* out) const;
+
 #ifdef SK_BUILD_FOR_ANDROID_FRAMEWORK
     /** Returns true if the caller is the only owner of the underlying path data */
     bool unique() const { return fPathRef->unique(); }