Move renderSamples() to DivDispatch implementations.

To prevent rendering samples for systems that are not in use.

Additionally, it gives the systems more flexibility to render the samples
according to their specific configuration.

src/engine/dispatch.h

@@ -438,6 +438,26 @@ class DivDispatch {
      */
     virtual const char** getRegisterSheet();
 
+    /**
+     * Get sample memory buffer.
+     */
+    virtual const void* getSampleMem(int index = 0);
+
+    /**
+     * Get sample memory capacity.
+     */
+    virtual size_t getSampleMemCapacity(int index = 0);
+
+    /**
+     * Get sample memory usage.
+     */
+    virtual size_t getSampleMemUsage(int index = 0);
+
+    /**
+     * Render samples into sample memory.
+     */
+    virtual void renderSamples();
+
     /**
      * initialize this DivDispatch.
      * @param parent the parent DivEngine.