From ca92d4a53b33014a3fe54654aefa9aaa2230e34b Mon Sep 17 00:00:00 2001
From: Mira Grudzinska <mira@lottiefiles.com>
Date: Tue, 4 Jun 2024 00:20:52 +0200
Subject: [PATCH] lottie: fix matte layer finding

Layer identifiers do not have to be unique within
the entire file - they are unique within a given
group. Searching the entire composition to find
the referenced matte was an incorrect approach.

Error introduced by 1ee79a6c2afafb6b16b14abc969b60c1dbc7a065

@Issue: https://github.com/thorvg/thorvg/issues/2349
---
 src/loaders/lottie/tvgLottieBuilder.cpp | 10 +++-------
 src/loaders/lottie/tvgLottieModel.h     |  9 +++++++++
 2 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/src/loaders/lottie/tvgLottieBuilder.cpp b/src/loaders/lottie/tvgLottieBuilder.cpp
index c5426b19..945c958c 100644
--- a/src/loaders/lottie/tvgLottieBuilder.cpp
+++ b/src/loaders/lottie/tvgLottieBuilder.cpp
@@ -98,7 +98,7 @@ struct RenderContext
 
 static void _updateChildren(LottieGroup* parent, float frameNo, Inlist<RenderContext>& contexts, LottieExpressions* exps);
 static void _updateLayer(LottieLayer* root, LottieLayer* layer, float frameNo, LottieExpressions* exps);
-static bool _buildComposition(LottieComposition* comp, LottieGroup* parent);
+static bool _buildComposition(LottieComposition* comp, LottieLayer* parent);
 static Shape* _draw(LottieGroup* parent, RenderContext* ctx);
 
 static void _rotateX(Matrix* m, float degree)
@@ -1315,7 +1315,7 @@ static void _attachFont(LottieComposition* comp, LottieLayer* parent)
 }
 
 
-static bool _buildComposition(LottieComposition* comp, LottieGroup* parent)
+static bool _buildComposition(LottieComposition* comp, LottieLayer* parent)
 {
     if (parent->children.count == 0) return false;
     if (parent->buildDone) return true;
@@ -1334,11 +1334,7 @@ static bool _buildComposition(LottieComposition* comp, LottieGroup* parent)
                     child->matteTarget = static_cast<LottieLayer*>(*(c - 1));
                 }
             //matte layer is specified by an index.
-            } else {
-                if (auto matte = comp->layerByIdx(child->mid)) {
-                    child->matteTarget = matte;
-                }
-            }
+            } else child->matteTarget = parent->layerByIdx(child->mid);
         }
 
         if (child->matteTarget) {
diff --git a/src/loaders/lottie/tvgLottieModel.h b/src/loaders/lottie/tvgLottieModel.h
index 8209f16a..2074a810 100644
--- a/src/loaders/lottie/tvgLottieModel.h
+++ b/src/loaders/lottie/tvgLottieModel.h
@@ -571,6 +571,15 @@ struct LottieLayer : LottieGroup
     Type type = Null;
     bool autoOrient = false;
     bool matteSrc = false;
+
+    LottieLayer* layerByIdx(int16_t idx)
+    {
+        for (auto child = children.begin(); child < children.end(); ++child) {
+            auto layer = static_cast<LottieLayer*>(*child);
+            if (layer->idx == idx) return layer;
+        }
+        return nullptr;
+    }
 };