Add NanoVG::beginFrame(Widget*) for convenience

dgl/NanoVG.hpp

@@ -298,6 +298,11 @@ public:
     */
     void beginFrame(int width, int height, float scaleFactor = 1.0f, Alpha alpha = PREMULTIPLIED_ALPHA);
 
+   /**
+      Begin drawing a new frame inside a widget.
+    */
+    void beginFrame(Widget* widget);
+
    /**
       Ends drawing flushing remaining render state.
     */

dgl/src/NanoVG.cpp

@@ -15,6 +15,7 @@
  */
 
 #include "../NanoVG.hpp"
+#include "../Window.hpp"
 
 // -----------------------------------------------------------------------
 
@@ -182,6 +183,14 @@ void NanoVG::beginFrame(int width, int height, float scaleFactor, Alpha alpha)
     nvgBeginFrame(fContext, width, height, scaleFactor, static_cast<NVGalpha>(alpha));
 }
 
+void NanoVG::beginFrame(Widget* widget)
+{
+    DISTRHO_SAFE_ASSERT_RETURN(widget != nullptr,);
+
+    Window& window(widget->getParentWindow());
+    nvgBeginFrame(fContext, window.getWidth(), window.getHeight(), 1.0f, NVG_PREMULTIPLIED_ALPHA);
+}
+
 void NanoVG::endFrame()
 {
     nvgEndFrame(fContext);