Allows for dynamic emissive textures in vanilla Minecraft.
If you want to make a solid texture emissive, just set the alpha value to 252 in your favorite image editor. You can see an example of this with redstone ore. Translucent textures require a bit more work. Check the example for ice to get a general idea of how this works.
return inputColor; means you're returning the color of the texture without any lighting applied. This is used for making something fully emissive.
return apply_partial_emissivity(); means the blocks with that alpha are only partially emissive, tinting it with a specific color of light. You can find a handy link to a table of light colors here: https://minecraft.fandom.com/wiki/Light?file=1.9_lighting_curves_%2528gamma%253D0%2529.png. Remember, colors in OpenGL are formatted as RGB values from 0 to 1!
return inputColor * lightColor; means you're simply returning the texture with its proper lighting. This is the default case.
This pack probably won't work with Optifine! If it does, good for you! This pack is supposed to be installed in the RESOURCE PACKS folder, using vanilla Minecraft on 1.20.2, because it is a RESOURCE PACK. If there's still a bug after doing everything correctly, report it in the issues tab at https://github.com/ShockMicro/VanillaDynamicEmissives/issues.