drawing on textures

i’m implementing an application which allows you to paint on 3D objects. in the moment i’m just changing the texture value at the point of the cursor. but actually i want to create different brushes with different shapes and sizes so maybe i can use the drawing methods of opengl - but how? how can i draw with opengl to a texture, without coping the whole scene to a texture - i just want to have the line in my texture and not the rest of the scene - is this possible?
thanks for your help

Have you tried using the render to texture extensions? http://www.google.com/search?num=20&hl=e…re+&btnG=Search