Non photorealistic rendering of trees and smoke using billboards
I apply and extend Morgan McGuire, Andi Fein, and Colin Hartnett's Real-time Cartoon Rendering of Smoke to the rendering of Pen-and-Ink Trees. For trees, the goal is to mimick the style of Computer-Generated Pen-and-Ink Illustration of Trees by Deussen and Strothotte.
The leaves are rendered with billboards. An additional billboard of the same shape (and shaded black) is drawn behind each leaf to create the outlines. By decreasing or increasing the distance between the outline billboard and the leaf billboard, the user can control how the number of outlines shown (and therefore how abstract the tree looks). By varying the outline billboard's size, the user can control the outline's width.
Trunks are exported from 3D studio Max files. Only their silhouettes are rendered. Leaves are generated along the tree branches using a simple stochastic algorithm. Shadow volumes are also supported.