[skottie] Animation::animationTick() -> Animation::seek()

Replace poorly defined animationTick() with a normalized seek() method.

TBR=
Change-Id: Id2ea17bb426fe86fede0d6c8a3d93236902f10af
Reviewed-on: https://skia-review.googlesource.com/130508
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>

3 files changed, 26 insertions, 15 deletions

diff --git a/modules/skottie/fuzz/FuzzSkottieJSON.cpp b/modules/skottie/fuzz/FuzzSkottieJSON.cpp
index e4f19ccad7..35135f133f 100644
--- a/modules/skottie/fuzz/FuzzSkottieJSON.cpp
+++ b/modules/skottie/fuzz/FuzzSkottieJSON.cpp
@@ -23,7 +23,7 @@ void FuzzSkottieJSON(sk_sp<SkData> bytes) {
     if (!animation) {
         return;
     }
-    animation->animationTick(1337); // A "nothing up my sleeve" number
+    animation->seek(0.1337f); // A "nothing up my sleeve" number
 }
 
 #if defined(IS_FUZZING_WITH_LIBFUZZER)
diff --git a/modules/skottie/include/Skottie.h b/modules/skottie/include/Skottie.h
index 0a89ca0438..906ea82b68 100644
--- a/modules/skottie/include/Skottie.h
+++ b/modules/skottie/include/Skottie.h
@@ -48,9 +48,27 @@ public:
 
     ~Animation() override;
 
-    void render(SkCanvas*, const SkRect* dst = nullptr) const;
-
-    void animationTick(SkMSec);
+    /**
+     * Draws the current animation frame.
+     *
+     * @param canvas   destination canvas
+     * @param dst      optional destination rect
+     */
+    void render(SkCanvas* canvas, const SkRect* dst = nullptr) const;
+
+    /**
+     * Updates the animation state for |t|.
+     *
+     * @param t   normalized [0..1] frame selector, where 0 == inPoint and 1 == outPoint.
+     */
+    void seek(SkScalar t);
+
+    /**
+     * Returns the animation duration in seconds.
+     */
+    SkScalar duration() const {
+        return (fOutPoint - fInPoint) / fFrameRate;
+    }
 
     const SkString& version() const { return fVersion;   }
     const SkSize&      size() const { return fSize;      }
diff --git a/modules/skottie/src/Skottie.cpp b/modules/skottie/src/Skottie.cpp
index 8396b5ba90..ddea1be18b 100644
--- a/modules/skottie/src/Skottie.cpp
+++ b/modules/skottie/src/Skottie.cpp
@@ -733,9 +733,7 @@ sk_sp<sksg::RenderNode> AttachNestedAnimation(const char* path, AttachContext* c
 
     protected:
         void onTick(float t) {
-            // map back from frame # to ms.
-            const auto t_ms = t * 1000 / fFrameRate;
-            fAnimation->animationTick(t_ms);
+            fAnimation->seek(t * fFrameRate / fAnimation->frameRate());
         }
 
     private:
@@ -1288,7 +1286,7 @@ Animation::Animation(const ResourceProvider& resources,
     fScene = sksg::Scene::Make(std::move(root), std::move(animators));
 
     // In case the client calls render before the first tick.
-    this->animationTick(0);
+    this->seek(0);
 }
 
 Animation::~Animation() = default;
@@ -1312,16 +1310,11 @@ void Animation::render(SkCanvas* canvas, const SkRect* dstR) const {
     fScene->render(canvas);
 }
 
-void Animation::animationTick(SkMSec ms) {
+void Animation::seek(SkScalar t) {
     if (!fScene)
         return;
 
-    // 't' in the BM model really means 'frame #'
-    auto t = static_cast<float>(ms) * fFrameRate / 1000;
-
-    t = fInPoint + std::fmod(t, fOutPoint - fInPoint);
-
-    fScene->animate(t);
+    fScene->animate(fInPoint + SkTPin(t, 0.0f, 1.0f) * (fOutPoint - fInPoint));
 }
 
 } // namespace skottie