How do you make parts of a texture glow in the dark?

[MollyBrewer]

In the midday sun position the pink gown was pretty, then when switched to the midnight sun position the flowers and stems glowed in the dark. The gown was still pink in the dark, but the flowers and stems had a slight pink glow that was so pretty. The gown was not a layered gown, it was one layer. How is that done on the texture to make certain parts of a texture glow in the dark?  Is it a setting in the build menu or is it something applied to the texture before uploading to SL?

If I need to do it in a photo editing program, what steps do I need to do to the texture?

I didn’t check to see who made the gown or the name of the gown and I never took a picture of it.

Thanks

[arton Rotaru]

You can create an emissive mask for a diffuse texture. The mask will go into the alpha channel of the texture, just like what we do for transparency. Emissive is not what we can set as glow in the build floater though. Emissive is what we know as Fullbright. White in the alpha channel is 100 % Fullbright, black is 0%. And all the greys inbetween make the rest the brightness.

So you just paint the areas which should have the "glow" more or less white, and everything else just plain black. Copy that layer into an alpha channel, save as 32 bit Targa (.tga). In-world you set the Alpha mode of the diffuse texture to Emissive in the build floater.

[Quarrel Kukulcan]

If the whole dress is one face, then, yes, what arton said: make a texture the exact same way you'd make one with parts of it opaque and parts of it transparent (opaque will be bright in the dark, transparent will not), upload it and assign it to the object's face in the usual way, then set that face's alpha mode to Emission Mask instead of Alpha Blending. That tells SL to treat the alpha layer as pixel-by-pixel illumination amounts instead of opacity ratings.

You may have to fight with your image editing program a little. The alpha layer is so commonly used to control opacity that a lot of paint programs don't know how to display it any other way. You also need to make sure your paint program doesn't black out totally clear pixels when it exports PNG or TGA files. (GIMP has a "Save color values from transparent pixels" option; I don't know about other programs.) If it doesn't have that option, you can work around it by using a very-low-but-not-0 alpha value for the pixels you don't want to glow.

Edited November 9, 2020 by Quarrel Kukulcan

[MollyBrewer]

thank you

Edited November 10, 2020 by MollyBrewer