[skotty] Cubic Bezier lerp

Change-Id: I7eda67fb89c1ef54f4bc1470d10ee5ab797a8b6e
Reviewed-on: https://skia-review.googlesource.com/91445
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>

2 files changed, 19 insertions, 10 deletions

diff --git a/experimental/skotty/SkottyAnimator.cpp b/experimental/skotty/SkottyAnimator.cpp
index d4c5c96c1a..7c4c16e780 100644
--- a/experimental/skotty/SkottyAnimator.cpp
+++ b/experimental/skotty/SkottyAnimator.cpp
@@ -43,12 +43,12 @@ void KeyframeInterval<ShapeValue>::lerp(float t, ShapeValue* v) const {
 }
 
 float AnimatorBase::ComputeLocalT(float t, float t0, float t1,
-                                  const SkPoint& c0, const SkPoint& c1) {
+                                  const SkCubicMap* cubicMap) {
     SkASSERT(t1 > t0);
     auto lt = (t - t0) / (t1 - t0);
 
-    if (c0 != SkPoint({0, 0}) || c1 != SkPoint({1, 1})) {
-        // TODO: lt = CubicBezier(lt, c0, c1);
+    if (cubicMap) {
+        lt = cubicMap->computeYFromX(lt);
     }
 
     return SkTPin<float>(lt, 0, 1);
diff --git a/experimental/skotty/SkottyAnimator.h b/experimental/skotty/SkottyAnimator.h
index f8d1c3abb6..1b519c9aa6 100644
--- a/experimental/skotty/SkottyAnimator.h
+++ b/experimental/skotty/SkottyAnimator.h
@@ -8,6 +8,8 @@
 #ifndef SkottyAnimator_DEFINED
 #define SkottyAnimator_DEFINED
 
+#include "SkCubicMap.h"
+#include "SkMakeUnique.h"
 #include "SkottyPriv.h"
 #include "SkottyProperties.h"
 #include "SkTArray.h"
@@ -29,7 +31,7 @@ protected:
 
     // Compute a cubic-Bezier-interpolated t relative to [t0..t1].
     static float ComputeLocalT(float t, float t0, float t1,
-                               const SkPoint& c0, const SkPoint& c1);
+                               const SkCubicMap*);
 };
 
 // Describes a keyframe interpolation interval (v0@t0) -> (v1@t1).
@@ -44,9 +46,8 @@ struct KeyframeInterval {
     float   fT0 = 0,
             fT1 = 0;
 
-    // Cubic Bezier interpolation control pts.
-    SkPoint fC0,
-            fC1;
+    // Initialized for non-linear lerp.
+    std::unique_ptr<SkCubicMap> fCubicMap;
 
     // Parse the current interval AND back-fill prev interval t1.
     bool parse(const Json::Value& k, KeyframeInterval* prev) {
@@ -75,8 +76,16 @@ struct KeyframeInterval {
         }
 
         // default is linear lerp
-        fC0 = ParsePoint(k["i"], SkPoint::Make(0, 0));
-        fC1 = ParsePoint(k["o"], SkPoint::Make(1, 1));
+        static constexpr SkPoint kDefaultC0 = { 0, 0 },
+                                 kDefaultC1 = { 1, 1 };
+        const auto c0 = ParsePoint(k["i"], kDefaultC0),
+                   c1 = ParsePoint(k["o"], kDefaultC1);
+
+        if (c0 != kDefaultC0 || c1 != kDefaultC1) {
+            fCubicMap = skstd::make_unique<SkCubicMap>();
+            // TODO: why do we have to plug these inverted?
+            fCubicMap->setPts(c1, c0);
+        }
 
         return true;
     }
@@ -95,7 +104,7 @@ public:
         const auto& frame = this->findInterval(t);
 
         ValT val;
-        frame.lerp(ComputeLocalT(t, frame.fT0, frame.fT1, frame.fC0, frame.fC1), &val);
+        frame.lerp(ComputeLocalT(t, frame.fT0, frame.fT1, frame.fCubicMap.get()), &val);
 
         fFunc(fTarget, val.template as<AttrT>());
     }