The Octagon Engine
Description:
A game engine demonstrating per-pixel lighting, bump mapping, shadow volumes and particles. It displays Quake 3 bsp maps, Quake 2 md2 and Quake 3 md3 models.
Everything visible is rendered with its decal texture multiplied by a small constant plus its emissive texture, in order to provide the base for adding light. Then, for each light, stencil shadows are cast for each object which the light influences, and then a hardware-specific codepath lights the surface. After all lights have been considered, particles are added.
For a more in-depth look at how the Octagon Engine works, see the technical information page.
More screenshots are available here.
Requirements:
For standard codepath:
OpenGL 1.3 support
2 texture units
8 bit destination alpha buffer
For NV20 codepath:
4 texture units
ARB_vertex_program
EXT_blend_color
NV_register_combiners
NV_texture_shader
For R200 codepath:
6 texture units
ARB_vertex_program
ATI_fragment_shader
Optional:
SGIS_generate_mipmap
HP_occlusion_test
NV_vertex_array_range, NV_vertex_array_range2 and NV_fence
ATI_vertex_array_object
Benchmarks:
I have tested this program on my AMD Athlon XP 2000+ with four different graphics cards. The frame rates were:
| nVidia GeForce 2 Integrated GPU (32 MB) | 5.4 fps |
| ATi Radeon 9000 (64 MB) | 15.9 fps |
| nVidia Geforce 3 Ti200 (64 MB) | 21.2 fps |
| nVidia Geforce FX 5900 XT (128 MB) | 37.4 fps |
References:
Quake 3 BSP
Quake 3 BSP Format, by Ben Humphrey. http://www.gametutorials.com
Unofficial Quake 3 map specs, by Kekoa Proudfoot. graphics.stanford.edu
MD3 Models
Description of MD3 format, by PhaethonH. http://linux.ucla.edu/~phaethon/q3/formats/md3format.html
MD2 Models
OpenGL Game Programming, by Hawkins and Astle. ISBN: 0-7615-3330-3
Shadow Volumes
Practical & Robust Stenciled Shadow Volumes for Hardware-Accelerated Rendering, by Cass Everitt and Mark J Kilgard. http://developer.nvidia.com
Nehe tutorials lesson 28 - stencil shadow volumes. nehe.gamedev.net
Lighting
Per-Pixel Lighting, by Philip Taylor. http://msdn.microsoft.com
Real-Time Per-Pixel Point Lights and Spot Lights, by Ron Frazier. http://www.ronfrazier.net/apparition
Texture Compositing with Register Combiners, by John Spitzer. http://developer.nvidia.com