Changing emissivity gradually with PRIM_ALPHA_MODE_EMISSIVE

[Rolig Loon]

According to the LSL wiki, when PRIM_ALPHA_MODE_EMISSIVE is enabled,  "Diffuse texture pixels opacity maps to their emissivity when rendered. Fully opaque pixels will effectively be rendered as ‘full bright’."  That implies that we should be able to vary emissivity gradually between zero and FULLBRIGHT by changing opacity while we have that alpha mode enabled. But I can't see how to do it with llSetLinkPrimitiveParamsFast.  Has anyone else figured this one out?

[Ron Khondji]

Is that not kinda described on the page about PRIM_ALPHA_MODE?

[KT Kingsley]

If you're asking about altering the emissivity dynamically, you'd need a series of textures with different alphas. It's the texture's alpha that's used rather than the face's.

[Rolig Loon]

12 minutes ago, Ron Khondji said:

Is that not kinda described on the page about PRIM_ALPHA_MODE?

No, it's not.  I quoted the entire "description" above.  It's about as clear as mud, sadly.

8 minutes ago, KT Kingsley said:

If you're asking about altering the emissivity dynamically, you'd need a series of textures with different alphas. It's the texture's alpha that's used rather than the face's.

Thanks.  I suspected as much, but was hoping for a simpler approach.  That does still leave me wondering what to do with the final parameter in 

[ PRIM_ALPHA_MODE, integer face, integer alpha_mode, integer mask_cutoff ]

since there is no mask cutoff in emissivity mode.  Time to do more experimenting.

[Qie Niangao]

Not sure the mask_cutoff means anything for emissive alpha mode, just as it doesn't mean anything for blended alpha.

It's true that the mode supports "gradual" emissivity, but that's gradual spatially over the surface of the texture, not so much temporally -- unless the texture is animated.

I have used alpha gradients with smooth texture animation to gradually pulse the "full-brightness" of the entire textured face - a neat effect that doesn't need a script once the texture animation is started. 

More often, though, I just use it to have some text and line art full-bright on a normally-lit surface, without needing to overlay textures.

[KT Kingsley]

The mask cutoff value only seems to do anything in masking mode, where it specifies the level in the alpha layer that switches between fully opaque and fully transparent.

[Rolig Loon]

25 minutes ago, Qie Niangao said:

Not sure the mask_cutoff means anything for emissive alpha mode, just as it doesn't mean anything for blended alpha.

That's the way it appeared to me --- sort of a dummy variable in that mode -- but it's good to have that verified.  Thanks.

27 minutes ago, Qie Niangao said:

I have used alpha gradients with smooth texture animation to gradually pulse the "full-brightness" of the entire textured face - a neat effect that doesn't need a script once the texture animation is started. 

And that's ideal.  Even better than what I was planning to do.  Thanks again.