Material Data

Warning!

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. For a more detailed explanation of the fundamentals of materials, see Pedro Toledo's Brief Considerations About Materials

Colors

Color

a solid color for the surface; Tints the color of the diffuse map.

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). The alpha channel of the Normal Map may contain a specular exponent value that is mutilplied by the "Glossiness" parameter. A higher alpha value will result in specular highlights that are brighter and tighter. 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 environment intensity. A lower value in the alpha channel will diminish the impact of the environment map reflections on the surface of the object.

Positioning

The Specular Map has its own set of the same Positioning & Scaling Properties properties as the Texture.

Texture Channel Encoding

How the renderer will treat each color value in a texture image channel

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	Specular exponent
Specular Map	Red	Green	Blue	Environment intensity

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 appears in the absence of light (ambiance): 0 = no additional ambiance (default); 255 = full brightness

Note that using any alpha mode other than Transparency may cause problems when rendered with viewers that do not yet support materials because they will be rendered as blended transparency. We expect that support for materials will be adopted quickly in most viewers, so this is acceptable.

Alpha Cutoff

Used only when Alpha Mode is Alpha Mask (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.

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 specular map’s alpha channel is present, the specular exponent map contained in it is modulated by this parameter.