Image and Video-based Non-Photorealistic Rendering / brush_stroke
Each Brush stroke is an object
with the following properties: Anchor point in image coordinates,
angle of orientation in degrees, width in pixels, lengths in both
directions from the anchor point in pixels,
Color (R, G, B) for the current and past several frames, and
opacity. In addition the brush stroke knows if it is ``new'' and/or
if it is ``Strong.''