Re: [osg-users] The Collada plugin and transparency

[Roger James]

Roger James wrote: If there is a texture present, then if transparency * transparent yields an opaque value (transparency.a * transparent == 1 in A_ONE mode) the we use source alpha as the blending constant. If transparent * transparency yields a transparent value then we put that value into the blenders constant colour alpha and use that as the bending constant. If there is no texture present then if transparency * transparent * mat.a yields an opaque value we do not turn the blender on. Otherwise we should put transparency * transparent * mat.a into the blenders constant colour alpha and use that as the bending constant. This effectively modifies the equations as follows (I think!) factor = transparent.a * transparency * mat.a fb.r = fb.r * (1.0f - factor ) + mat.r * factor fb.g = fb.g * (1.0f - factor ) + mat.g * factor fb.b = fb.b * (1.0f - factor ) + mat.b * factor fb.a = fb.a * (1.0f - factor) + mat.a * factor Sorry, I got the equations wrong/unclear as usual. They should be:- 1. Texture present and transparent.a * transparency opaque fb.r = fb.r * (1.0f - mat.a ) + mat.r * mat.a fb.g = fb.g * (1.0f - mat.a) + mat.g * mat.a fb.b = fb.b * (1.0f - mat.a) + mat.b * mat.a fb.a = fb.a * (1.0f - mat.a) + mat.a * mat.a 2. Texture present and transparent.a * transparency not opaque factor = transparent.a * transparency fb.r = fb.r * (1.0f - factor ) + mat.r * factor fb.g = fb.g * (1.0f - factor ) + mat.g * factor fb.b = fb.b * (1.0f - factor ) + mat.b * factor fb.a = fb.a * (1.0f - factor) + mat.a * factor 3. No texture and transparency * transparent * mat.a not opaque factor = transparent.a * transparency * mat.a fb.r = fb.r * (1.0f - factor ) + mat.r * factor fb.g = fb.g * (1.0f - factor ) + mat.g * factor fb.b = fb.b * (1.0f - factor ) + mat.b * factor fb.a = fb.a * (1.0f - factor) + mat.a * factor On looking at equation 3 it would probably need to be partially implemented in a shader as mat.a is the result of the lighting calculation. But then I am not sure how you would turn the blender off! So it is probably better use the the diffuse alpha instead of mat.a, or maybe ignore mat.a altogether. Comments anyone? Roger

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