Hi,

I am making a custom sky color set for X-Plane 11 based on real-life scattering equations. While the same real-life scattering equations will be used in upcoming Enhanced Skyscapes, which will have a custom sky system, I wanted to implement a simpler temporary version based on default sky color system until Enhanced Skyscapes is finished. Does anyone know about how X-Plane's sky color textures work? It has a rather... interesting format:

Based on my experiments, first 8 of the 128x32 sky colors (from "night" to "aft", inclusive) are not used at all. Remaining 8 of the 128x32 sky colors represent sun being 90, 4, 2, 0, -2, -4, -8 and -90 degrees below horizon respectively.

Based on the description, 8 vertical stripes are supposed to control ambient light, sun direct light, sun color, moon color, water color, unlit parts of clouds, lit parts of clouds and moon direct light respectively. However most of them do not seem to have any effect, other than "direct light". For unlit and lit parts of clouds, bottom-most 128x128 squares seem to be used instead, but I have no idea how exactly they are formatted.

I found @Murmur's thread on this, which seems to be rather outdated, so I am pretty much lost.

Thanks in advance.

Edited April 27, 20215 yr by BiologicalNanobot

Yeah, after my past experiments I gave a description of how X-Plane used the texture.

Your conclusions are about right, from what I recall. Regarding the sky colors, I think the sun elevation doesn't need to be +/-90 to use the morn/night textures, they're already completely used for a low sun elevation of +/-10 degrees or so, IIRC.

Also, the lowermost 1 or 2 stripes of each 128x32 texture is used for something like fog/haze color, IIRC.

Only a few of the 8 vertical stripes have the effects their name suggest, others control things like:

moon reflection on water;

sun reflection on water;

color inside clouds at the bottom of cloud;

color inside clouds at the top of cloud;

and other various things like reflections, etc.

The 128x128 cloud textures are used for direct and ambient cloud light. IIRC, the X axis represents the sun elevation, the Y axis represents the cloud height. So the colors of a cloud puff depend on its height and on the sun elevation. The color of clouds can be indipendently modulated by a couple datarefs whose name I don't remember ("cloud ambient" and "cloud direct" something).

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In general, the final environment lighting is calculated with shaders, and the sky_colors textures are only used as a starting point. That's why modifying the sky_colors textures doesn't allow complete control over final result. Sky_colors textures are basically legacy textures, on which subsequent shaders have been added.

An easy way to check how they work, is making a texture completely black, leaving only a single element (e.g. a stripe) with a primary color and experimenting with the results inside X-Plane (using the provided sky colors console).

Anyway, I think at this point XP12 (hopefully with a totally new lighting system) will come out, before something decent can be obtained by modifying XP11 textures/shaders... 😬