lottie/builder: Fix overlapped stroking outlines.

Previously, the builder accumulated the outlines and fills
in one paint to reduce the rendering context.

However, this approach won't work for Lottie
if the resource contains multiple strokes with branched groups.

We should apply the optimization
only when the specified condition is satisfied.

src/loaders/lottie/tvgLottieBuilder.cpp

@@ -56,7 +56,8 @@ struct RenderContext
     LottieObject** begin = nullptr; //iteration entry point
     RenderRepeater* repeater = nullptr;
     float roundness = 0.0f;
-    bool fragmented = false;  //context has been separated. allow adding visual properties(fill/stroking) if it is false.
+    bool stroking = false;     //context has been separated by the stroking
+    bool reqFragment = false;  //requirment to fragment the render context
 
     RenderContext()
     {
@@ -77,7 +78,6 @@ struct RenderContext
             *repeater = *rhs.repeater;
         }
         roundness = rhs.roundness;
-        fragmented = rhs.fragmented;
     }
 };
 
@@ -229,26 +229,30 @@ static void _updateStroke(LottieStroke* stroke, int32_t frameNo, RenderContext&
 }
 
 
+static bool _fragmentedStroking(LottieObject** child, queue<RenderContext>& contexts, RenderContext& ctx)
+{
+    if (!ctx.reqFragment) return false;
+    if (ctx.stroking) return true;
+
+    contexts.push(ctx);
+    auto& fragment = contexts.back();
+    fragment.propagator->stroke(0.0f);
+    fragment.begin = child - 1;
+    ctx.stroking = true;
+
+    return false;
+}
+
+
 static void _updateSolidStroke(LottieObject** child, int32_t frameNo, queue<RenderContext>& contexts, RenderContext& ctx)
 {
-    //the rendering context is fragmented
-    if (ctx.propagator->strokeWidth() > 0.0f) {
-        contexts.push(ctx);
-        auto& fragment = contexts.back();
-        fragment.propagator->stroke(0.0f);
-        fragment.begin = child - 1;
-        _updateSolidStroke(child, frameNo, contexts, fragment);
-        ctx.fragmented = true;
-        return;
-    }
-
-    if (ctx.fragmented) return;
+    if (_fragmentedStroking(child, contexts, ctx)) return;
 
     auto stroke = static_cast<LottieSolidStroke*>(*child);
 
     ctx.merging = nullptr;
     auto color = stroke->color(frameNo);
-    ctx.propagator->stroke(color.rgb[0], color.rgb[1], color.rgb[2], stroke->opacity(frameNo));
+    ctx.propagator->stroke(color.rgb[0], color.rgb[1], color.rgb[2], stroke->opacity(frameNo));    
 
     _updateStroke(static_cast<LottieStroke*>(stroke), frameNo, ctx);
 }
@@ -256,18 +260,7 @@ static void _updateSolidStroke(LottieObject** child, int32_t frameNo, queue<Rend
 
 static void _updateGradientStroke(LottieObject** child, int32_t frameNo, queue<RenderContext>& contexts, RenderContext& ctx)
 {
-    //the rendering context is fragmented
-    if (ctx.propagator->strokeWidth() > 0.0f) {
-        contexts.push(ctx);
-        auto& fragment = contexts.back();
-        fragment.propagator->stroke(0.0f);
-        fragment.begin = child - 1;
-        _updateGradientStroke(child, frameNo, contexts, fragment);
-        ctx.fragmented = true;
-        return;
-    }
-
-    if (ctx.fragmented) return;
+    if (_fragmentedStroking(child, contexts, ctx)) return;
 
     auto stroke = static_cast<LottieGradientStroke*>(*child);
 
@@ -280,7 +273,7 @@ static void _updateGradientStroke(LottieObject** child, int32_t frameNo, queue<R
 
 static void _updateFill(LottieSolidFill* fill, int32_t frameNo, RenderContext& ctx)
 {
-    if (ctx.fragmented) return;
+    if (ctx.stroking) return;
 
     ctx.merging = nullptr;
 
@@ -294,7 +287,7 @@ static void _updateFill(LottieSolidFill* fill, int32_t frameNo, RenderContext& c
 
 static Shape* _updateFill(LottieGradientFill* fill, int32_t frameNo, RenderContext& ctx)
 {
-    if (ctx.fragmented) return nullptr;
+    if (ctx.stroking) return nullptr;
 
     ctx.merging = nullptr;
 
@@ -723,6 +716,7 @@ static void _updateChildren(LottieGroup* parent, int32_t frameNo, queue<RenderCo
 
     while (contexts.size() > 0) {
         auto& ctx = contexts.front();
+        ctx.reqFragment = parent->reqFragment;
         for (auto child = ctx.begin; child >= parent->children.data; --child) {
             //TODO: Polymorphsim?
             switch ((*child)->type) {
@@ -966,6 +960,40 @@ static void _bulidHierarchy(LottieGroup* parent, LottieLayer* child)
 }
 
 
+//TODO: Optimize this. Can we preprocess in the parsing stage?
+static void _checkFragment(LottieGroup* parent)
+{
+    if (parent->children.count == 0) return;
+
+    int strokeCnt = 0;
+
+    /* Figure out if the rendering context should be fragmented.
+       Multiple stroking or grouping with a stroking would occur this.
+       This fragment resolves the overlapped stroke outlines. */
+    for (auto c = parent->children.end() - 1; c >= parent->children.data; --c) {
+        switch ((*c)->type) {
+            case LottieObject::Group: {
+                if (strokeCnt > 0) {
+                    parent->reqFragment = true;
+                    return;
+                }
+                break;
+            }
+            case LottieObject::SolidStroke:
+            case LottieObject::GradientStroke: {
+                if (strokeCnt > 0) {
+                    parent->reqFragment = true;
+                    return;
+                }
+                ++strokeCnt;
+                break;
+            }
+            default: break;
+        }
+    }
+}
+
+
 static bool _buildPrecomp(LottieComposition* comp, LottieGroup* parent)
 {
     if (parent->children.count == 0) return false;
@@ -983,6 +1011,8 @@ static bool _buildPrecomp(LottieComposition* comp, LottieGroup* parent)
             if (child->matte.target->refId) _buildReference(comp, child->matte.target);
         }
         _bulidHierarchy(parent, child);
+
+        _checkFragment(static_cast<LottieGroup*>(*c));
     }
     return true;
 }

src/loaders/lottie/tvgLottieModel.h

@@ -482,6 +482,8 @@ struct LottieGroup : LottieObject
     Scene* scene = nullptr;               //tvg render data
 
     Array<LottieObject*> children;
+
+    bool reqFragment = false;   //requirment to fragment the render context
 };