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Quote from Nocte

Even if I could, there are some other projects I'd enjoy working on more. I don't know how to make it more efficient, I only have an idea how to make one that supports color. It's probably a bit too resource-heavy to include in Vanilla, but it would make a nice mod. I'll post it behind a spoiler, just in case anyone finds it useful.

The following is an idea of how to add colored blocklight to Minecraft as a mod. There's a chance it won't work, but it looks good on paper.


Storage

We're not going to use RGB colors internally, but xyY. The 'Y' (capital Y) here is luminance, and this corresponds nicely to the system Minecraft already has. We'll have to extend the light map with the remaining x and y, or chromaticity. I'm not sure if the usual 4 bits per ordinate will provide enough resolution to blend lights nicely, but using 8 bits sounds wasteful. Let's play it safe and go with 4 bits. So this costs 1 byte per block. It could be stored in a map file as a new NBT field, but this is optional. It would also be nice if this could be sent over the network, but I'm not sure if this can be done without sending a Vanilla client into a tailspin.

The color of a lamp is not specified in RGB, but in chromaticity as well. (This means you can't make a brown lamp, but you can make a dim red one and get almost the same results. It's actually pretty close to how light works in real life.)


Generating

Light physics work a bit strange in Minecraft; two lamps don't shine brighter than one. And we'd like to keep it that way, so Y stays the way Vanilla works. To calculate (x,y) we'll take some kind of weighed average of all contributing lamps. Cool trick: we can do a simple weighed linear interpolation on the chroma, and end up with a good approximation of what it would look like if we actually had several lights with different intensities shining on the same surface.

"Some kind of weighed average" is a bit vague on purpose. There's some of room for experimentation here to find out what looks nicest and doesn't grind the game to a halt. As per usual, we use the current minichunk (16x16x16) and its Moore neighbours to do all calculations in. The naive approach would be to pathfind back to all lamps we've found in the previous step, and blend them weighed according to their distance. Slow as molasses, doesn't use any extra memory, and accurate.

Another approach would be to keep the current "wavefront" way of spreading light, but to store some additional info in the wavefront about the contributing lights. Fast, small memory footprint, but not accurate. It could leave hard edges where the lamps should have been blended.

Yet another one would be to keep temporary maps for each lamp, generate them the Vanilla way, and then average all chromas using the light level as the weight. (The end result Y would be the maximum of all Y's.) Fast, uses gobs of memory, accurate.


Rendering

Everyone who has ever tried to make a colored light mod fondly remembers 1.7 beta, where you could simply set the vertex colors and be done with it. So one way to make this work is to revert back to this system. Players however prefer the increased FPS and smoother transitions of 1.8.

It would be nice if we could use shaders, but Minecraft runs on a wide variety of hardware because it uses OpenGL's fixed pipeline. So instead we'll do it the old-fashioned way through multitexturing. We need:

1. An 1x16 sunlight texture, mapping intensity to color. This one gets updated all the time for dusk and dawn.
2. A 16x256 texture for translating xyY back to RGB. This one gets updated for torchlight flicker.

Translating xyY to RGB is a good candidate for a lookup table. If we use 4 bits for x and y, and the usual 4 bits for Y, we can conveniently map it to a 16x256 texture. The combiner is then set up as follows:

1. Blocklight, GL_REPLACE
2. Sunlight, GL_ADD
3. Vertex coloring, GL_MODULATE (bind a dummy texture, no texture coordinates)
4. Block texture, GL_MODULATE

The only reason this works is because the output of stage 2 gets clamped. This is how sunlight "overpowers" block light. 1.8 did this clamping in code, when the light texture was generated. We do the same, but now in hardware.


Modding & compatibility

This mod could exist as a client mod, a server mod, or both. As a pure client-side mod, it would be for decorative purposes only. As a server-side mod, it could be used to make color-specific light sensors. (A vanilla client wouldn't see the colored light, but the sensors would still work as advertised.)

Quote from CodenameDuchess

I support, with no hesitations. Although if this was implemented, I might start yearning for a colored light source block. Never mind, I think I already am.

Quote from CodenameDuchess

I support, with no hesitations. Although if this was implemented, I might start yearning for a colored light source block. Never mind, I think I already am.

Quote from Neonkeks

It might be a great idea, but would someone do this at any time? I can't java this to script a mod!! Someone thought about to do this as a mod? If yes, then develope this...