Q3Radiant Shader Manual

1 Preface: Making Your Own Shaders

2 Introduction

2.1 What is a Shader?

For Quake III Arena,Shader scripts are located in quake3/baseq3/scripts.

A Quake III Arena shader file consists of a series of surface attribute and rendering instructions formatted within braces ("{" and "}"). Below you can see a simple example of syntaxand format for a single process, including the Q3MAP keywords or "SurfaceParameters", which follow the first bracket and a single bracketed "stage":

textures/liquids/lava
	{
	deformVertexes wave sin 0 3 0 0.1
	tessSize 64
	{
	map textures/common/lava.tga
	}
}

2.2 Shader Name & File Conventions

Shaders that are only going to be referenced by the gamecode, not modeling tools, often are just a single world, like"projectionShadow" or "viewBlood".

Shaders that are used on characters or other polygon models need to mirror a .tga file, which allows the modelers to build with normal textures, then have the special effects show up when the model is loaded into the game.

Shaders that are placed on surfaces in the map editor commonly mirror a .tga file, but the "qer_editorimage" shader parameter canforce the editor to use an arbitrary image for display.

Shader pathnames have a case sensitivity issue - on windows, they aren't case sensitive, but on unix they are. Try to always use lowercase for filenames, and always use forward slashes "/" for directory separators.

2.3 Shader Types

The remaining global keywords, and all Stage Specific Keywords are processed by the renderer. They are appearance changes only and have no effect on game play or game mechanics. Changes to any of these attributes will take effect as soon as the game goes to another level or vid_restarts (type command vid_restart in the game console).

Shader keywords are notcase sensitive.

IMPORTANT NOTE: some of the shader commands may be order dependent, so it's good practice to place all global shader commands (keywords defined in this section) at the very beginning of the shader and to place shader stages at the end (see various examples).

2.4 Key Concepts

· Game unit: A game unit is used by deformations to specify sizes relative to the world. Game units are the same scale we have had since way back in the Wolfensteindays - 8 units equals one foot. The default texture scale used by the Q3Radiant map editor results in two texels for each game unit, but that can be freely changed.

· Color units: Colors scale the values generated by the texture units to produce lighting effects. A value of 0.0 will be completely black, and a value of 1.0 will leave the texture unchanged. Colors are sometimes specified with a single value to be used across all red, green,and blue channels, or sometimes as separate values for each channel.

· Texture units: This is the normalized (see above) dimensions of the original texture image (or a previously modified texture at a given stage in the shader pipeline). A full texture, regardless of its original size in texels, has a normalized measurement of 1.0 x 1.0. For normal repeating textures, it is possible to have value greater than 1.0 or less than 0.0, resulting in repeating of the texture. The coordinates are usually assigned by the level editor or modeling tools, but you still need to be aware of this for scrolling or turbulent movement of the texture at runtime.

Sin: Sin standsfor sine wave, a regular smoothly flowing wave ranging from -1 to 1.
Triangle: Triangle is a wave with a sharp ascent and a sharp decay, ranging from 0 to 1.It will make a choppy looking wave forms.
Square: A squarewave simply switches from -1 to 1 with no in-between.
Sawtooth: In the sawtooth wave, the ascent is like a triangle wave from 0 to 1, but the decay cuts off sharply back to 0.
Inversesawtooth: This is the reverse of the sawtooth… instant ascent to the peak value (1), then a triangle wave descent to the valley value (0). The phase on this goes from 1.0 to 0.0 instead of 0.0 to 1.0. This wave is particularly usefulfor additive cross-fades.

Waveforms all have thefollowing properties:
<base> Where the wave form begins. Amplitude is measured from this base value.
<amplitude> This is the height of the wave created, measured from the base. You will probably need to test and tweak this value to get it correct for each new shader stage. The greater the amplitude, the higher the wave peaks and the deeper the valleys.
<phase> This is a normalized value between 0.0 and 1.0. Changing phase to a non-zero value affects the point on the wave at which the wave form initially begins to be plotted. Example: In Sin or Triangle wave, a phase of 0.25 means it begins one fourth (25%) of the way along the curve, or more simply put, it begins at the peak of the wave. A phaseof 0.5 would begin at the point the wave re-crosses the base line. A phase of 0.75 would be at the lowest point of the valley. If only one wave form is being used in a shader, a phase shift will probably not be noticed and phase should have a value of zero (0). However, including two or more stages of the same process in a single shader, but with the phases shifted can be used to create interesting visual effects. Example: using rgbGen in two stages with different colors and a 0.5 difference in phase would cause the manipulated texture to modulate between two distinct colors. Phase changes can also be used when you have two uses of the same effect near each other, and you don't want them to be synchronized. You would write a separate shader for each, changing only the phase value.
<freq>Frequency. This value is expressed as repetitions or cycles of the wave per second. A value of 1 would cycle once per second. A value of 10 would cycle 10 times per second. A value of 0.1 would cycle once every 10 seconds.

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