Add Canvas::Image.dirtyPixels()

simgear/canvas/elements/CanvasImage.cxx

@@ -947,6 +947,14 @@ SGRect<int> intersectRect(const SGRect<int>& a, const SGRect<int>& b)
     }
       
     image->setColor(color, x, y);
+  }
+
+    void Image::dirtyPixels()
+    {
+        osg::ref_ptr<osg::Image> image = _texture->getImage();
+        if (!image)
+            return;
+        image->dirty();
         auto c = getCanvas().lock();
         c->enableRendering(true); // force a repaint
     }

simgear/canvas/elements/CanvasImage.hxx

@@ -115,6 +115,11 @@ namespace canvas
       
       void setPixel(int x, int y, const osg::Vec4& color);
 
+      /**
+        * mark the image pixels as modified, so the canvas is re-painted
+       */
+      void dirtyPixels();
+      
       osg::ref_ptr<osg::Image> getImage() const;
       
     //  void setRow(int row, int offset, )