[SKY] Greyscale to Palette Alpha/Color in BSEffectShaderProperty

[abies]

Hello - my first post here, so please be forgiving if I have missed some obvious link or explanation.

 

I'm trying to understand how BSEffectShaderProperty flags SLSF1_Greyscale_to_PaletteAlpha and SLSF1_Greyscale_to_PaletteColor work. I understand the general idea - Greyscale Texture is used as palette and it is being indexed on u,v based on some transformation of original pixels. What I'm trying to understand is how this works exactly.

 

From my tests so far, closest I was able to get is that for alpha, horizonal coordinate equals to Source texture alpha and vertical coordinate equals to falloff computed from falloff angles. It works almost ok (I use Dungeons\AzurasStar\AzuraEpicCrystal05.nif as my test object, with base mesh removed, so only two decal meshes with palettes are visible).

For PaletteColor I'm at loss. It looks a bit like greyscale average of source texture.rgb is used as vertical coordinate, but thats not fully accurate (could be issue of (r+g+b)/3 versus more accurate greyscale conversion) - and what with horizontal coordinate?

 

Does anybody know how exactly these things are used? In particular PaletteAlpha.

[grond]

Welcome to the Alliance, and congratulations on making the greatest first post I've ever read.    Sorry I can't help with your question.  Little too deep for me. 

[abies]

Managed to find out how it is done.

 

h - horizontal coordinate

v - vertical coordinate

 

for PaletteColor,

h = sourceTexture.g*emissiveMultiple

v = emissiveColor.r*emissiveMultiple

result.rgb = GreyscalePalette(h,v).rgb

 

for PaletteAlpha

h = sourceTexture.a

v = emissiveColor.a*falloff

result.a = GreyscalePalette(h,v).a

 

Not sure where vertex colors are coming in equation - will they modify h or v parameter -  cannot find example with vertex colors at the moment.

Edited August 31, 2013 by abies

[megapatato]

[many years later...]

An example of a mesh with vertex colors is the daedric armor (e.g. daedriccuirass_1.nif). The main armor component uses the environment map shader to yield metal-like reflections. The glow component is handled by the BSEffectShaderProperty node on a separate piece of geometry. This glowing geometry has light emission, texture translation (i.e. V coordinate offset), and vertex transparency.

A) the texture used is VaporTile02.dds but its alpha / transparency is overridden via the Grayscale_To_PaletteAlpha (in shader flags 1), which signals using the grayscale image in GradDusguiseShader02.dds to remap / regenerate alpha values based on the formula described above by abies.

B) texture translation is handled by the BSEffectShaderPropertyFloatController (i.e. it changes the V coordinate of the UV mapping as a function of time)

C) in addition, the vertices themselves have alpha values, allowing the glow to have both sharp edges (close to the armor) and falloff regions (away from the armor). In the image attached, I set the alpha value of the three left-most vertices to various levels (labeled on the image). To view these changes in NifSkope 2.0dev7, one has to save changes, and reload from file (seems NifSkope cashes vertex alpha values and won't refresh them when changed).

So, point A turns the opaque texture into a translucent one, and point C allows the "glow" to dim / strengthen as the geometry requires it.