Create masking functionality

For a project we're doing we need masking functionality in the following matter: A masking sprite exists in the scene. A line is drawn on top of it with Vectrosity (a line drawing plugin). The line needs to be masked by the visible part of the sprite. See enclosed image for details. This can be achieved by custom shaders. If you are good with shaders, you can achieve this fairly quickly. Use the enclosed project to work in and deliver the project back with your solution.