non-photorealistic rendering techniques for a game engine

The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL

Adrian Ilie

Non-Photorealistic Rendering Techniques for a Game Engine

COMP 238 Final Project

The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL

Adrian Ilie

Remember NPR Quake?

The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL

Adrian Ilie

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

The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL

Adrian Ilie

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

The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL

Adrian Ilie

Silhouettes

Flip the normals and extend the edges of backfacing polygons.

The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL

Adrian Ilie

Creases (1)

Add thin quadrilaterals at each edge, forming an angle with the polygon.

The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL

Adrian Ilie

Creases (2)

• It actually works!

The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL

Adrian Ilie

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).

The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL

Adrian Ilie

Cartoon-style shading

• 1D texture• coordinate at

vertex = amount of light received

The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL

Adrian Ilie

Walls

• No lighting information available, so…

• Replace with “hand-drawn” texture.

• Add charcoal style for lines (one thick line and several jittered thin lines).

The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL

Adrian Ilie

Result

The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL

Adrian Ilie

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.