creating a drawing tool via openCV

Hey all, I’m just exploring openframeworks a little bit trying to create simple tools. Quick question for the moment is for example, if I am creating drawing tool using openCV, (ellipse corrosponds to blobs centroid.x and blobs centroid.y) and using the drawn “stroke” as a sort of eraser to to reveal a quicktime movie behind. Everything works at the moment- quicktime plays behind properly, blobs reveal the video through an opengL blend mode, the only thing I’m stuck with is now I can’t make the blob which I attached an ellipse with more like a paintbrush. Any pointers?
Trawling around the forum I’ve read about rendering to texture and adjusting the clear buffer to create a trail effect which would do what I want. I would do something similar in Jitter but I’m not really sure at the moment how to implement this and if it would affect the opengl call I programmed earlier to simulate a multiply blend mode in photoshop. Need help desperately!
Thanks in advance!

Progress! got the FBO to work, but where do I set it to not clear the color buffer? Using this post as a guide.