I'm trying to understand how to interpret the <transparency> and <transparent> elements in some of the default materials.
The phong material has:
and the diffuse color has an alpha component.
For materials in DirectX and OpenGL, the opacity of the object usually goes in the alpha component of the diffuse color.
I may be misunderstanding the collada spec, but my reading of the spec
is that the transparent and transparency elements allow you to take
into account the color and intensity of refracted light when computing
the color of a surface. The spec says that the refracted light is
added to the reflected light. This is something that the standard DX
and OGL lighting models do not account for.
However, I think the Max, Maya, and SoftImage exporters are
using the <transparent> and <transparency> elements just to control
the opacity of a material. They either set <transparency> to 1.0 and
use a gray-scale color for <transparent>, or vice versa. This may be
a way of working around a deficiency in the collada spec that does
not allow you to specify both a diffuse color and a diffuse texture.
If you don't look at the transparency/transparent elements, the only
way to have a partially transparent textured object would be to
hard-code the transparency in the alpha channel of the texture.
How are other people handling this? I don't care about refracted light in my shading, but I do want to be able to set a constant opacity for textured objects.
this post may have the information you are looking for.