Material Data
The information in this page applies to the work being done in the STORM-1905 Normal & Specular Maps (aka Materials) Project. None of this will work until that has been completed and released - and until that time, it may be subject to change.
This page describes how the various parameters and texture data used to define a material in Second Life are interpreted for rendering. It is intended to help content creators and external tool developers to better understand how to create images to achieve good visual results.
There are as many as two colors and three images associated with a face.
Colors
- Color
- a solid color for the surface; not used if a Texture is also specified
- Specular Color
- this is a color that ‘tints’ any reflections from the face; see also Specular Map
Textures
Texture
Also called the Diffuse Map, this is an image that is displayed on the surface. The way the texture is applied to the face is controlled by
Positioning & Scaling Properties
Note that each image (diffuse/texture, normal map, specular map) has its own values for these parameters.
- Mapping
- Default or Planar
- Horizontal Repeats
- number of repeats of the image over the surface (used only in default mapping)
- Vertical Repeats
- number of repeats of the image over the surface (used only in default mapping)
- Rotation
- clockwise degrees the image is rotated
- Repeats Per Meter
- number of repeats of the image per in-world meter of the surface (used only in planar mapping)
- Horizontal Offset
- distance in meters the image is shifted right on the surface
- Vertical Offset
- distance in meters the image is shifted up on the surface
Normal Map
An image whose color data encodes changes to the "normal" for each pixel on the surface. The normal is the direction that the pixel "faces" for the purpose of determining how it is illuminated by and reflects light sources (imagine that each pixel is turned on tiny pivots). Keep in mind these are OpenGL style normal maps, where bright green is up and bright red is right. For details on what a normal map is and for a sample normal map see http://en.wikipedia.org/wiki/Normal_mapping. See also the Texture Channel Encoding table below.
- Positioning
- The Normal Map has its own set of the same Positioning & Scaling Properties properties as the Texture.
Specular Map
This encodes the color of the light reflected by each pixel on the surface. See the Texture Channel Encoding table below.
The Alpha channel value of the Specular Map encodes the specular exponent, or "Glossiness" of the surface. A lower value in the alpha channel will make specular highlights broader and more diffuse, like in plastic or rough stone, while a higher value will make specular highlights tighter and brighter, like in metal or polished stone/wood.
- Positioning
- The Specular Map has its own set of the same Positioning & Scaling Properties properties as the Texture.
Texture Channel Encoding
| Parameter | Red | Green | Blue | Alpha |
|---|---|---|---|---|
| Diffuse Map | Red | Green | Blue | selectable
see Alpha Mode |
| Normal Map | Normal X Axis | Normal Y Axis | Normal Z Axis | Currently unused |
| Specular Map | Red | Green | Blue | Specular exponent |
Additional Parameters
- Alpha Mode
- This controls the interpretation of the Alpha channel data in the Diffuse Map. It can have one of four values:
- None
- Alpha channel data is not used
- Transparency (blended)
- The value is a degree of transparency (255 = opaque, 0 = fully transparent)
- Alpha Mask (cutoff)
- The value (0...255) is compared to the Alpha Cutoff parameter (below); if the pixel is greater than the cutoff, it is fully opaque; if not, it is fully transparent.
- Emissive
- The value is used to encode how brightly the pixel emits light (glows): 0 = no glow; 255 = full brightness
- Alpha Cutoff
- Used only when Alpha Mode is Alpha Test (see description of that mode above)
- Specular Light Color
- Tints the light reflected from the object; this value is combined with any value from the color for the pixel as specified in the Specular Map, if any.
- Environment Intensity
- Modulates the intensity of the environment on the surface as a whole. When an environment mask is present in the specular map, the environment mask is modulated by this to provide better control over the intensity of the environment that’s being reflected (some parts of the surface can reflect the environment more or less than others).
- Glossiness
- This controls the “glossiness”, or the roughness, of the reflected light on a surface. The lower this value is, the “rougher” the light reflectance is, while the higher the value the “sharper” the light reflectance is. When the normal map’s alpha channel is present, the specular exponent map contained in it is modulated by this parameter.