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Go for the GT5 look using vertex and fragment shaders!

Introduction

GPU Shaders (normally called vertex and fragment shaders) are supported in Racer through Cg. Cg was created by nVidia to overcome a lot of the troubles when creating shaders for a multitude of graphics hardware. Racer has always targeted for high-end hardware, and Cg probably is one of the areas where that becomes obvious.

This document is not about teaching you Cg; there's enough of that online. I'd recommend getting the book 'The Cg Tutorial' from nVidia, which can be read online for free at http://http.developer.nvidia.com/CgTutorial/cg_tutorial_chapter01.html (see also below)

More information on generic Racer shaders (the name 'shader' here is a bit confusing) can be found here; Cg shaders are only a part of the larger concept of Racer shaders.

External books/pages to read

There's a lot of information on Cg on the internet. nVidia has made available for free the texts of their excellent GPU Gems series. Try the following (they are all for free):

• Cg Tutorial book (an excellent reference guide if you want to learn how to write Cg shaders)
• GPU Gems 1
• GPU Gems 2 (link is weird, 12-2-09)
• GPU Gems 3

Entry points

Every Cg shader file must have an entry point for its vertex or fragment program. In Racer, this should be 'main' for both the vertex program and the fragment program. Essentially, this means that each shader must be in its own file (you can't add the vertex & fragment shader in the same file).

CG Parameters available in vertex/fragment shaders

Cg shader parameters are searched for in Racer. There are a number of ways to determine semantic meaning but I've chosen a (somewhat less elegant, but simple) way of needing exact variable names. So if the variable below states 'modelViewProj' for example, you really need to use 'uniform float4x4 modelViewProj' as the declaration in your shader; something like 'uniform float4x4 modelVwPrj' will NOT work).

Most variables are only available since Racer v0.7.2.

Geometrical parameters

Shader library

Racer (v.0.7.2+) comes with a number of global shaders, located in data/renderer/shaders_hdr and shaders_ldr (HDR since v0.7.4). The creation of Cg shaders is not trivial and more something that programmers tend to do. Graphics artists do need some technical knowledge to be able to use Cg effectively, but can rely on most often-used Cg shaders being present.

More on HDR can be found here. The main importance is that HDR shaders are stored in a separate directory; data/renderer/shaders_hdr. They are mostly similar to the LDR shaders. LDR though, is deprecated and will not be maintained. HDR looks so much better and is needed to get to the GT5/PGR look.

The shaders are normally prefixed with standard for default effects (such as normal lighting, bumpmapping, detailmapping) and are prefixed with dyn_standard if they are for movable objects; mostly this means car objects. The dyn (for dynamic) Cg shaders use a variable 'modelMatrix' to apply transformations to vertices & normals. The non-dynamic shaders are faster (since they skip on some matrix multiplications); that's there only reason for existing versus the dynamic versions.

The global shader library consists of the following files (all postfixed with .cg):

Shaders for static objects (non-moving track objects)

Shaders for dynamic objects

These shaders are used for dynamic objects such as cars. For all these you need at least Racer v0.8.0.

Special shaders using in other parts of the render engine

These shaders are not normally used for your cars & tracks, but are explained here for completeness.

Shader library for debugging

These shaders are normally only used when you need to check things.

vf_standard
{
  vertex_shader 
  {
    file=standard_v.cg
  }
  fragment_shader
  {
    file=check_shader_f.cg
  }
}
shader_guardrail~vf_standard
{
  layer0
  {
    map=guardrail.tga
  }
}

          

Fun with shaders

Check out these articles on specific things done with Cg shaders:

• Waving flags on your tracks with standard_wave_v/f.
• Glowing brake discs.
• Full-screen shaders.

(last updated November 12, 2009 )