Added covers, cross-fade

src/items/InteractiveObject.h

@@ -23,13 +23,14 @@ namespace ZL {
 		Eigen::Vector3f pivot = Eigen::Vector3f::Zero(); // local-space offset to rotation pivot
 		float rotationY = 0.0f;          // Y-axis rotation in radians
 		float scale     = 1.0f;          // uniform scale
+		float alpha     = 1.0f;          // opacity: 1=opaque, 0=fully transparent
 		float interactionRadius;
 		bool isActive    = true;
 		bool isAnimating = false;        // true while a timed animation is running
 		std::string activateFunctionName;
 
 		struct AnimTask {
-			enum class Type { Move, Rotate, Scale } type;
+			enum class Type { Move, Rotate, Scale, Fade } type;
 			Eigen::Vector3f startPos;
 			float startRotY;
 			float startScale;
@@ -48,6 +49,7 @@ namespace ZL {
 		void moveTo(const Eigen::Vector3f& target, float durationSec, std::function<void()> onComplete = {});
 		void rotateTo(float targetRotY, float durationSec, std::function<void()> onComplete = {});
 		void scaleTo(float targetScale, float durationSec, std::function<void()> onComplete = {});
+		void fadeTo(float targetAlpha, float durationSec, std::function<void()> onComplete = {});
 		void update(int64_t deltaMs);
 		void draw(Renderer& renderer) const;
 	};