Stroked digital art

Looking through the galleries of the Facebook Graffiti app one finds impressive examples of art people make despite its very simple interface.

What does one want in a drawing program? Start with a circular brush of color and opacity specified. The umbra of the brush optionally has a "penumbra" of user-specified thickness through which the opacity decays to zero (fully transparent). Next the brush may be be squashed to an ellipse and rotated to any angle.

Be able to control the thickness of the brush via stylus pressure. Allow calligraphy: the stylus may be rotated.

Zoom.

Layers. Translucency. One layer as an alpha mask.

Undo. Store both a complete edit history -- every stroke and action and time. This gives insight into the mind of the artist, how the final product was created. Open source art. And be able to access an abbreviated history, with the undos spliced out.

A palette of previous colors and brushes. A dropper for select a previous stroke (possibly from an undo history) and reapply it. Or select its color or brush. Dropper interface might be first select all strokes under a given point. Narrow by layer, time, approximate color or shape.

Insert an image as a layer for the purposes of tracing. Image transformations: rotate translate, linear transforms. One intends the image not be visible in the final product, but there is nothing stopping you.

Although the file format is open, we limit the interface so that every stroke is purely created by hand. No copy and paste. It's kind of a cross between Photoshop and Illustrator but crippled in some places.

Select individual spline points. Strokes that gradually change color are possible.

It's all encoded underneath with splines, so it's a vector format. An artist could design a mural on a small handheld device.

Open source art. On commission, or sale, or releasing to public domain for say government-supported "stimulus" art, the complete edit history is available so the buyer can go on to modify.