1、为图层添加渲染器和读取器，分离图层基础信息、渲染和读写；

2、LayerTreeLayerNode持有MapLayer图层引用，为右键菜单做准备；
3、改名：imageviewer → mapcavas，mapcavas持有MapLayer图层引用，为刷新图像做准备；

HPPA/RasterLayer.h

@@ -1,6 +1,11 @@
 #pragma once
 
 #include "MapLayer.h"
+#include <memory>
+#include <QImage>
+
+class RasterDataProvider;
+class RasterRenderer;
 
 class RasterLayer : public MapLayer
 {
@@ -10,5 +15,25 @@ public:
 
     LayerType layerType() const override;
 
-    // future: renderer, data provider, etc.
+    // Access provider/renderer
+    RasterDataProvider* dataProvider() const;
+    RasterRenderer* renderer() const;
+
+    // Create or open provider based on this layer's uri
+    bool openDataProvider();
+
+    struct RenderParams {
+        double rWave = 665.0; // default wavelengths (nm)
+        double gWave = 560.0;
+        double bWave = 490.0;
+        double minValue = 0.0; // optional stretch
+        double maxValue = 255.0;
+    };
+
+    // Render the raster using current provider and renderer. Returns an empty QImage on failure.
+    QImage render(const RenderParams& params);
+
+private:
+    std::unique_ptr<RasterDataProvider> m_provider;
+    std::unique_ptr<RasterRenderer> m_renderer;
 };