1. Non-Photorealistic Rendering Techniques for a Game Engine
COMP 238 Final Project
Non-Photorealistic Rendering Techniques for a Game Engine

2. Remember NPR Quake?

3. How did they do it? “grep”-ed the Quake source code for OpenGL calls
Pulled them out into one source file
Added dynamic loading support
Started coding different visual styles

4. How about a “cartoon” look?
Silhouettes
Creases
Shading
Shadows
Walls

5. Silhouettes
Flip the normals and extend the edges of backfacing polygons.

6. Creases (1)
Add thin quadrilaterals at each edge, forming an angle with the polygon.

7. Creases (2)
It actually works!

8. Shadows The function is there, but it’s never called :(.
Just draw a projection of each model on a horizontal plane (not always correct, but works out pretty well).

9. Cartoon-style shading
1D texture
coordinate at vertex = amount of light received

10. Walls No lighting information available, so…
Replace with “hand-drawn” texture.
Add charcoal style for lines (one thick line and several jittered thin lines).

11. Result

12. Bibliography
[1] Alex Mohr, Michael Gleicher: "Non-Invasive, Interactive, Stylized Rendering". The 2001 ACM Symposium on Interactive 3D Graphics.
[2] Ramesh Raskar: "Hardware Support for Non-photorealistic Rendering", Eurographics 2001.
[3] Bert Freudenberg, Maic Masuch, Thomas Strothotte: "Walk-Through Illustrations: Frame-Coherent Pen-and-Ink Style in a Game Engine", Siggraph/Eurographics Graphics Hardware, LA, 2001.
[4] Adam Lake, Carl Marshall, Mark Harris, Marc Blackstein: "Hardware Support for Non-photorealistic Rendering", Siggraph/Eurographics Graphics Hardware, LA, 2001.
[5] Jeff Lander: "Shades of Disney: Opaquing a 3D World", Game Developer Magazine, March 2000.