renderer/picture: added a method to search for a paint object

This utility method allows access to a specific paint instance
by its unique identifier.

Experimental API:
- const Paint* Picture::paint(uint32_t id)
- const Tvg_Paint* tvg_picture_get_paint(Tvg_Paint* paint, uint32_t id)

inc/thorvg.h

@@ -1339,6 +1339,21 @@ public:
      */
     Result load(uint32_t* data, uint32_t w, uint32_t h, bool premultiplied, bool copy = false) noexcept;
 
+    /**
+     * @brief Retrieve a paint object from the Picture scene by its Unique ID.
+     *
+     * This function searches for a paint object within the Picture scene that matches the provided @p id.
+     *
+     * @param[in] id The Unique ID of the paint object.
+     *
+     * @return A pointer to the paint object that matches the given identifier, or @c nullptr if no matching paint object is found.
+     *
+     * @see Accessor::id()
+     *
+     * @note Experimental API
+     */
+    const Paint* paint(uint32_t id) noexcept;
+
     /**
      * @brief Sets or removes the triangle mesh to deform the image.
      *

src/bindings/capi/thorvg_capi.h

@@ -2071,6 +2071,22 @@ TVG_API Tvg_Result tvg_picture_set_size(Tvg_Paint* paint, float w, float h);
 TVG_API Tvg_Result tvg_picture_get_size(const Tvg_Paint* paint, float* w, float* h);
 
 
+/*!
+* \brief Retrieve a paint object from the Picture scene by its Unique ID.
+*
+* This function searches for a paint object within the Picture scene that matches the provided @p id.
+*
+* \param[in] paint A Tvg_Paint pointer to the picture object.
+* \param[in] id The Unique ID of the paint object.
+
+* \return A pointer to the paint object that matches the given identifier, or @c nullptr if no matching paint object is found.
+*
+* \see tvg_accessor_generate_id()
+* \note experimental API
+*/
+TVG_API const Tvg_Paint* tvg_picture_get_paint(Tvg_Paint* paint, uint32_t id);
+
+
 /** \} */   // end defgroup ThorVGCapi_Picture
 
 

src/bindings/capi/tvgCapi.cpp

@@ -582,6 +582,13 @@ TVG_API Tvg_Result tvg_picture_get_size(const Tvg_Paint* paint, float* w, float*
 }
 
 
+TVG_API const Tvg_Paint* tvg_picture_get_paint(Tvg_Paint* paint, uint32_t id)
+{
+    if (!paint) return nullptr;
+    return (Tvg_Paint*) reinterpret_cast<Picture*>(paint)->paint(id);
+}
+
+
 /************************************************************************/
 /* Gradient API                                                         */
 /************************************************************************/

src/loaders/lottie/thorvg_lottie.h

@@ -78,7 +78,7 @@ public:
      * @note Experimental API
      */
     const char* marker(uint32_t idx) noexcept;
-    
+
     /**
      * @brief Creates a new LottieAnimation object.
      *

src/renderer/tvgPicture.cpp

@@ -214,3 +214,26 @@ uint32_t Picture::mesh(const Polygon** triangles) const noexcept
     if (triangles) *triangles = pImpl->rm.triangles;
     return pImpl->rm.triangleCnt;
 }
+
+
+const Paint* Picture::paint(uint32_t id) noexcept
+{
+    struct Value
+    {
+        uint32_t id;
+        const Paint* ret;
+    } value = {id, nullptr};
+
+    auto cb = [](const tvg::Paint* paint, void* data) -> bool
+    {
+        auto p = static_cast<Value*>(data);
+        if (p->id == paint->id) {
+            p->ret = paint;
+            return false;
+        }
+        return true;
+    };
+
+    tvg::Accessor::gen()->set(this, cb, &value);
+    return value.ret;
+}