Description

Scrawl is a springy-mouse-follower drawing tool/toy.

Applet

Algorithm

A number of individual tracking points follow the mouse at slightly different rates. During each frame those points move towards the mouse and plot their positions. The varying tracking rates create tendrils of color that can resemble Moire patterns, or the "Qix"-style line-bounce of "Mystify" screen savers.

Color is accumulated in an additive manner using a higher resolution pixel buffer. The additional precision of this itermediate buffer allows for the gradual accumulation of very smooth gradients.

The additional precision is also used to plot antialiased sub-pixels, further smoothing the display. (this is effectively equivalent to 2x oversampling, then downsampling with a simple box filter)

A similar sub-pixel plotting method was used to render the images in the IFS Color Gallery.

Applications

By wrapping up a number of tracking points within a "brush" container such that they are constrained to follow along behind the "width" of the brush, as if each "mini-scrawl" were a bristle of the larger brush, some interesting painterly texture effects can be achieved.

History

See the Tracker page for similar earlier work.

Acknowledgements

I believe that Paul Schmidinger's Grappa applet is using a similar technique. While my original intent was not to duplicate Paul's work, after seeing it I can't claim that it didn't have an influence on the final result, so credit is due. Paul has a number of other interesting visual effects applets posted also. Recommended.