Real Time Shadows for Animated Crowds
in Virtual Cities

Céline Loscos, Franco Tecchia, Yiorgos Chrysanthou
University College London, Gower Street, London WC1E 6BT

In this paper, we address the problem of shadow computation for large environments including thousands of dynamic objects. The assumption of the method is that the model is 2.5D, which is often the case for virtual cities. We propose a method which exploits this property, avoiding complex visibility computation. We apply our method for virtual cities populated by thousands of walking humans, which are rendered in our case with impostors, allowing real time simulation.

In this paper, we treat the cases of shadows cast by buildings on humans, and by humans on the ground. To avoid 3D computation, we represent the shadows cast by buildings onto the environment with a 2.5D shadow map. When humans move, we quickly access the shadow information at the current location with a 2D grid. For each new position of the human, we compute the coverage of the human by the shadow and we display it with low cost using multi-texturing hardware. We also use the property of impostor to display the shadow of humans on the ground plane, by projecting the impostor relatively to the light source.

The method is currently limited to sharp shadows and a single light source. However approximations could be made to allow non-accurate soft-shadows. We show in the result that the computation of the shadows as well as the display is done in real time, and that the method could be easily extended for real time moving light sources.

Keywords: Shadow computation, dynamic shadows, real time rendering, populated virtual cities, multi-texturing.

PDF

Images: Method

Videos 

All videos are encoded with MPEG4 better known as DivX and are recorded in real time and full screen , on a PC Intel Pentium III 833MHz with an NVIDIA GeForce GTS2 64MB. A DivX codec can be found at http://www.projectmayo.com/ .

Navigation in the model with 10.000 humans, without shadows.	Format/size
	MPEG4 5.33MB QuickTime 4.86MB
Navigation in the model with 10.000 humans, with shadows of buildings on the ground.
	MPEG4 6.96MB QuickTime 6.27MB
Navigation in the model with 10.000 humans, with shadows of the buildings and the humans on the ground.
	MPEG4 7.61MB QuickTime 7.10MB
Navigation in the model with 10.000 humans, with shadows of the buildings, the humans onto the ground, and humans shaded.
	MPEG4 7.43MB QuickTime 15.3MB
Navigation in the model with 10.000 humans, at midday.
	MPEG4 3.07MB QuickTime 7.27MB
Navigation in the model with 10.000 humans, in late afternoon.
	MPEG4 3.25MB QuickTime 7.27MB