loader lottie: ++optimization.

Aggressive parallelization is implemented to perform updates
on every frame in an asynchronous manner.

src/lib/tvgLoadModule.h

@@ -44,9 +44,11 @@ public:
     virtual bool resize(Paint* paint, float w, float h) { return false; }
 
     virtual bool animatable() { return false; }  //true if this loader supports animation.
+    virtual void sync() {};  //finish immediately if any async update jobs.
 
     virtual bool read() = 0;
     virtual bool close() = 0;
+
     virtual unique_ptr<Surface> bitmap() { return nullptr; }
     virtual unique_ptr<Paint> paint() { return nullptr; }
 };

src/lib/tvgPictureImpl.h

@@ -109,7 +109,8 @@ struct Picture::Impl
                     }
                     if (paint) return RenderUpdateFlag::None;
                 }
-            }
+            } else loader->sync();
+
             if (!surface) {
                 if ((surface = loader->bitmap().release())) {
                     loader->close();

src/loaders/lottie/tvgLottieBuilder.cpp

@@ -377,25 +377,19 @@ bool LottieBuilder::update(LottieComposition* comp, int32_t frameNo)
 }
 
 
-unique_ptr<Scene> LottieBuilder::build(LottieComposition* comp)
+void LottieBuilder::build(LottieComposition* comp)
 {
-    if (comp->scene) {
-        TVGERR("LOTTIE", "LottieBuilder::build() is requested multiple times?");
-        return unique_ptr<Scene>(comp->scene);
-    }
+    if (comp->scene) return;
 
-    auto scene = Scene::gen();
-    if (!scene) return nullptr;
-    comp->scene = scene.get();
+    comp->scene = Scene::gen().release();
+    if (!comp->scene) return;
 
     //TODO: Process repeater objects?
 
-    if (!update(comp, 0)) return nullptr;
+    if (!update(comp, 0)) return;
 
     //viewport clip
     auto clip = Shape::gen();
     clip->appendRect(0, 0, static_cast<float>(comp->w), static_cast<float>(comp->h));
-    scene->composite(std::move(clip), CompositeMethod::ClipPath);
-
-    return scene;
+    comp->scene->composite(std::move(clip), CompositeMethod::ClipPath);
 }

src/loaders/lottie/tvgLottieBuilder.h

@@ -30,7 +30,7 @@ struct LottieComposition;
 struct LottieBuilder
 {
     bool update(LottieComposition* comp, int32_t frameNo);
-    unique_ptr<Scene> build(LottieComposition* comp);
+    void build(LottieComposition* comp);
 };
 
 #endif //_TVG_LOTTIE_BUILDER_H

src/loaders/lottie/tvgLottieLoader.cpp

@@ -75,12 +75,16 @@ void LottieLoader::clear()
 
 void LottieLoader::run(unsigned tid)
 {
-    LottieParser parser(content);
-    parser.parse();
-
-    comp = parser.comp;
-
-    root = builder->build(comp);
+    //update frame
+    if (comp && comp->scene) {
+        builder->update(comp, frameNo);
+    //initial loading
+    } else {
+        LottieParser parser(content);
+        parser.parse();
+        comp = parser.comp;
+        builder->build(comp);
+    }
 }
 
 
@@ -143,6 +147,8 @@ bool LottieLoader::header()
             p = e;
             continue;
         }
+        //TODO: need a duration time in advance.
+
         //width
         if (!strncmp(p, "\"w\":", 4)) {
             p += 4;
@@ -251,7 +257,7 @@ bool LottieLoader::read()
     if (!content || size == 0) return false;
 
     //the loading has been already completed in header()
-    if (root) return true;
+    if (comp) return true;
 
     TaskScheduler::request(this);
 
@@ -273,7 +279,7 @@ unique_ptr<Paint> LottieLoader::paint()
 {
     this->done();
 
-    return std::move(root);
+    return cast<Paint>(comp->scene);
 }
 
 
@@ -287,7 +293,9 @@ bool LottieLoader::frame(uint32_t frameNo)
 
     this->frameNo = frameNo;
 
-    return builder->update(comp, frameNo);
+    TaskScheduler::request(this);
+
+    return true;
 }
 
 
@@ -302,8 +310,6 @@ uint32_t LottieLoader::totalFrame()
 
 uint32_t LottieLoader::curFrame()
 {
-    this->done();
-
     return frameNo;
 }
 
@@ -314,4 +320,10 @@ float LottieLoader::duration()
 
     if (!comp) return 0;
     return comp->duration();
+}
+
+
+void LottieLoader::sync()
+{
+    this->done();
 }

src/loaders/lottie/tvgLottieLoader.h

@@ -41,8 +41,6 @@ public:
     LottieBuilder* builder = nullptr;
     LottieComposition* comp = nullptr;
 
-    unique_ptr<Scene> root;             //current motion frame
-
     bool copy = false;                  //"content" is owned by this loader
 
     LottieLoader();
@@ -62,6 +60,7 @@ public:
     uint32_t totalFrame() override;
     uint32_t curFrame() override;
     float duration() override;
+    void sync() override;
 
 private:
     bool header();