The background: a grayscale version of the source image
Three shapes: a square, a circle, and a triangle
The square is filled with the red fraction of the source image
The circle is filled with the green fraction of the source image
The triangle is filled with the blue fraction of the source image
The common part of any two shapes is filled with the combintaion of two fractions, e.g. the common part of the square and the triangle is filled with the combination of the red and blue fractions of the source image
The common part of all the three shapes is filled with the combination of all the RGB fractions, which should result in the source image colors
User interface:
All three shapes can be moved with the mouse. Use left and right mouse button, and a shift key for moving the square, circle and triangle respectively
Technical requirements:
All the drawing should be flicker-free
Only the source image can be used (don't use the grayscale and colour versions created with some graphics processing application)