Stippling styles for popuped models

Experiences: It seems the spiral mask can do more precise control over the density in the space, but slower. The direction of the spiral mask has not much influence on the effects.
Randomly control the direction of the spiral mask.

Clockwise direction

Anti-clockwise direction

The rendered popuped model is merged from the original image and the lighted model by multiplication.

The popuped model after smoothing and doing process to the hair

(a)

(b)
The order of placement is based on the intensity of the rendered popuped model. The space of each stipple is based on the intensity.(a) and (b) have different lighting conditions.