When making materials with transparency you have three Mode options: Composite Blend, Additive Blend, or Alpha Test.
For each of the examples below we will be using this opacity map
Alpha Test
When you first add an opacity map to a material the Transparency Mode is set to Alpha Test. With Alpha Test what is transparent is determined by a threshold value between 0.01-1. By default the Threshold value is set to 0.5. This corresponds 50% grey in the opacity map. Any pixel in the opacity map that is less than or equal 50% grey will result in the material being completely transparent. Any pixel greater than 50% grey will be completely opaque.
In IMVU Studio when using Alpha Test you have the ability to adjust the Threshold, which is the bias between black and white at which a pixel in the opacity map will be rendered transparent. If you slide the Threshold toward 0 the bias makes less of the material transparent and if you slide the Threshold toward 1 the bias makes more of the material transparent.
NOTE: This feature is only available in IMVU Studio and not available in Classic Client Creator. In the Classic Creator when ‘Use blending’ is unchecked the threshold is set 0.5 and cannot be changed.
Composite Blend
One of the two blending modes, Composite Blend uses the full greyscale range of the opacity map to determine transparency. Grey values of the opacity map that are closer to black appear more transparent and values that are closer to white appear more opaque. Black is completely transparent and White is completely opaque.
Using Composite Blend does come with some caveats:
- When used with maps that enable reflectivity, a shininess map or normal map, you may see a halo or ghost in areas of the material that you would expect to be completely transparent (see Transparency – Opacity Masking for more info on this).
- Sometimes you might see one transparent material unexpectedly in front of another (see Transparency – Priority for more info on this).
- Using Double Sided with either blending modes can produce unexpected results.
Additive Blend
The other blending mode, Additive Blend works much the same way as Composite Blend except it does not require an opacity map! Setting a material to Additive Blend changes how the material is displayed against the what is behind it. Instead of drawing over what is behind, with Additive Blend material is “added” (literally mathematically) with what is behind. This results in things in the scene appearing “lightened” by an object with an Additive Blend material.
The color values in the diffuse map determine the amount of “lightening”. Colors closer to black lighten less, colors closer to white lighten more. Black does not lighten at all and appears as completely transparent.
The color hues in the diffuse map affect the tint of the lightening.
When an opacity map is used it is combined with the diffuse map to affect the transparency like when used in Composite Blend material.
Because Additive Blend materials “lighten” what behind they can be used to make nice “glow” materials, especially when combined with Emission!
Additive Blend materials are subject to the same caveats as Composite Blend materials.
