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

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(); }

include/core/SkPathRef.h

@@ -271,6 +271,8 @@ public:
      */
     uint32_t writeSize() const;
 
+    void interpolate(const SkPathRef& ending, SkScalar weight, SkPathRef* out) const;
+
     /**
      * Gets an ID that uniquely identifies the contents of the path ref. If two path refs have the
      * same ID then they have the same verbs and points. However, two path refs may have the same

src/core/SkPath.cpp

@@ -193,6 +193,33 @@ void SkPath::swap(SkPath& that) {
     }
 }
 
+bool SkPath::isInterpolatable(const SkPath& compare) const {
+    int count = fPathRef->countVerbs();
+    if (count != compare.fPathRef->countVerbs()) {
+        return false;
+    }
+    if (!count) {
+        return true;
+    }
+    if (memcmp(fPathRef->verbsMemBegin(), compare.fPathRef->verbsMemBegin(),
+               count)) {
+        return false;
+    }
+    return !SkToBool(memcmp(fPathRef->conicWeights(), compare.fPathRef->conicWeights(),
+            fPathRef->countWeights() * sizeof(*fPathRef->conicWeights())));
+}
+
+bool SkPath::interpolate(const SkPath& ending, SkScalar weight, SkPath* out) const {
+    int verbCount = fPathRef->countVerbs();
+    if (verbCount != ending.fPathRef->countVerbs()) {
+        return false;
+    }
+    out->reset();
+    out->addPath(*this);
+    fPathRef->interpolate(*ending.fPathRef, weight, out->fPathRef);
+    return true;
+}
+
 static inline bool check_edge_against_rect(const SkPoint& p0,
                                            const SkPoint& p1,
                                            const SkRect& rect,

src/core/SkPathRef.cpp

@@ -299,6 +299,19 @@ void SkPathRef::copy(const SkPathRef& ref,
     SkDEBUGCODE(this->validate();)
 }
 
+
+void SkPathRef::interpolate(const SkPathRef& ending, SkScalar weight, SkPathRef* out) const {
+    const SkScalar* inValues = &ending.getPoints()->fX;
+    SkScalar* outValues = &out->getPoints()->fX;
+    int count = out->countPoints() * 2;
+    for (int index = 0; index < count; ++index) {
+        outValues[index] = outValues[index] * weight + inValues[index] * (1 - weight);
+    }
+    out->fBoundsIsDirty = true;
+    out->fIsOval = false;
+    out->fIsRRect = false;
+}
+
 SkPoint* SkPathRef::growForRepeatedVerb(int /*SkPath::Verb*/ verb,
                                         int numVbs,
                                         SkScalar** weights) {

tests/PathTest.cpp

@@ -3904,6 +3904,49 @@ public:
     }
 };
 
+static void test_interp(skiatest::Reporter* reporter) {
+    SkPath p1, p2, out;
+    REPORTER_ASSERT(reporter, p1.isInterpolatable(p2));
+    REPORTER_ASSERT(reporter, p1.interpolate(p2, 0, &out));
+    REPORTER_ASSERT(reporter, p1 == out);
+    REPORTER_ASSERT(reporter, p1.interpolate(p2, 1, &out));
+    REPORTER_ASSERT(reporter, p1 == out);
+    p1.moveTo(0, 2);
+    p1.lineTo(0, 4);
+    REPORTER_ASSERT(reporter, !p1.isInterpolatable(p2));
+    REPORTER_ASSERT(reporter, !p1.interpolate(p2, 1, &out));
+    p2.moveTo(6, 0);
+    p2.lineTo(8, 0);
+    REPORTER_ASSERT(reporter, p1.isInterpolatable(p2));
+    REPORTER_ASSERT(reporter, p1.interpolate(p2, 0, &out));
+    REPORTER_ASSERT(reporter, p2 == out);
+    REPORTER_ASSERT(reporter, p1.interpolate(p2, 1, &out));
+    REPORTER_ASSERT(reporter, p1 == out);
+    REPORTER_ASSERT(reporter, p1.interpolate(p2, 0.5f, &out));
+    REPORTER_ASSERT(reporter, out.getBounds() == SkRect::MakeLTRB(3, 1, 4, 2));
+    p1.reset();
+    p1.moveTo(4, 4);
+    p1.conicTo(5, 4, 5, 5, 1 / SkScalarSqrt(2));
+    p2.reset();
+    p2.moveTo(4, 2);
+    p2.conicTo(7, 2, 7, 5, 1 / SkScalarSqrt(2));
+    REPORTER_ASSERT(reporter, p1.isInterpolatable(p2));
+    REPORTER_ASSERT(reporter, p1.interpolate(p2, 0.5f, &out));
+    REPORTER_ASSERT(reporter, out.getBounds() == SkRect::MakeLTRB(4, 3, 6, 5));
+    p2.reset();
+    p2.moveTo(4, 2);
+    p2.conicTo(6, 3, 6, 5, 1);
+    REPORTER_ASSERT(reporter, !p1.isInterpolatable(p2));
+    p2.reset();
+    p2.moveTo(4, 4);
+    p2.conicTo(5, 4, 5, 5, 0.5f);
+    REPORTER_ASSERT(reporter, !p1.isInterpolatable(p2));
+}
+
+DEF_TEST(PathInterp, reporter) {
+    test_interp(reporter);
+}
+
 DEF_TEST(PathContains, reporter) {
     test_contains(reporter);
 }