what is unity_lightAtten? the meaning of each component?

[JohnSonLi]

what is the meaning of each component of this variable?

[Teravisor]

That’s one question with hard-to-find answer. The only information I could dig up(it’s so old it’s not funny and no docs at all):

uniform vec4 unity_4LightAtten0;
// scale factors for attenuation with squared distance
…
Depending on your platform and version of Unity … you might have to use unity_LightAtten[4] instead of unity_4LightAtten0

https://en.wikibooks.org/wiki/GLSL_Programming/Unity/Multiple_Lights

This quote is old, but might help(unfortunately, links are long dead).

@Aras

It’s a bit complicated, and more details at rendering pipeline talk at Unite 2012: http://unity3d.com/unite/uniteslides/Unite2012-Unity_Rendering_Pipeline.zip

LightMode=Vertex pass: 4 lights are set up, always sorted from brightest to dimmest, in unity_LightColor[n], unity_LightPosition[n], unity_LightAtten[n]. So fetching first index always gives you the brightest light.

LightMode=ForwardBase pass: _LightColor0 is the color of the main directional light that this pass is supposed to apply.
LightMode=ForwardAdd pass: the same; it’s the color of the per-pixel light that this pass is applying.

If your shader pass doesn’t have any LightMode tags, then no light variables are set up. So you’ll be getting garbage from previous objects that were affected by lights.

http://forum.unity3d.com/threads/cg-shader-light-color.151535/

Also, I’ve seen that attenuation used to compute like that (in several shaders):

float atten = 1.0 / (1.0 + lengthSq unity_LightAtten.z);*

I’ve never seen it used in any other form in any shaders I could find.

[bgolus]

It’s listed in UnityShaderVariables.cginc:

    // x = cos(spotAngle/2) or -1 for non-spot
    // y = 1/cos(spotAngle/4) or 1 for non-spot
    // z = quadratic attenuation
    // w = range*range
    half4 unity_LightAtten[8];

It does not appear that .w is used in any code anymore, likely because they clamp the light range using a stencil mask now.

[JohnSonLi]

@Teravisor

That’s one question with hard-to-find answer. The only information I could dig up(it’s so old it’s not funny and no docs at all):

https://en.wikibooks.org/wiki/GLSL_Programming/Unity/Multiple_Lights

This quote is old, but might help(unfortunately, links are long dead).

http://forum.unity3d.com/threads/cg-shader-light-color.151535/

Also, I’ve seen that attenuation used to compute like that (in several shaders):

I’ve never seen it used in any other form in any shaders I could find.

thx

[JohnSonLi]

@bgolus

It’s listed in UnityShaderVariables.cginc:

    // x = cos(spotAngle/2) or -1 for non-spot
    // y = 1/cos(spotAngle/4) or 1 for non-spot
    // z = quadratic attenuation
    // w = range*range
    half4 unity_LightAtten[8];

It does not appear that .w is used in any code anymore, likely because they clamp the light range using a stencil mask now.

thx…got it