Snow shader with perlin noise

I added snow effect feature into a toon shader I'm using (MKToon Free). I utilized basically this: https://forum.unity.com/threads/snow-up-vector-shader.177606/

MKToon's v2f struct:

Code (CSharp):

1. struct VertexOutputForward {
2.     float4 pos : SV_POSITION;
3.     float2 uv_Main : TEXCOORD0;
4.  
5.     float4 posWorld : TEXCOORD1;
6.     half3 normalWorld : TEXCOORD2;
7.     half3 tangentWorld : TEXCOORD3;
8.     half3 binormalWorld : TEXCOORD4;
9. ...
10. };
11.  

Inside MKToon I modified SurfaceColor function.

Code (CSharp):

1.    
2. //get surface color based on blendmode and color source
3. void SurfaceColor(out fixed3 albedo, out fixed alpha, float2 uv, half3 normal) {
4.    fixed4 c = tex2D(_MainTex, uv) * _Color;  
5.    float difference = dot(normal, _SnowDirection.xyz);
6.    if(difference >= _SnowLevel) {
7.       albedo = _SnowColor.rgb;
8.    }
9.    else {
10.       albedo = c.rgb;
11.    }
12.  
13.    alpha = c.a;
14. }

Here's outcome when it's only partly snowy:


It looks fine on small surfaces but e.g. on large grounds it's more on/off effect (no snow/full snow). What I really want is in the first example here using perlin noise: https://www.alanzucconi.com/2018/08/18/shader-showcase-saturday-6/

"The snowy transition seen in Overland can be replicated using a grayscale, smooth noise texture. The UV coordinates of the ground mesh are used to sample a colour from that texture."

I tinkered with this shader months ago and didn't get the sampling working, mostly because I'm not very adept with shader language. I added _NoiseTexture for perlin noise texture and tried to take samples

Code (CSharp):

1. float surfaceNoiseSample = tex2D(_NoiseTex, uv).r;
2. if(difference >= _SnowLevel) {
3.     albedo = surfaceNoiseSample > 0.75 ? _SnowColor.rgb : c.rgb;
4. }
5. else ...

but this has no effect, instead snow doesn't appear at all. Should I use tex2D(_NoiseTex, UvOfNoiseTex) like in here: https://github.com/IronWarrior/ToonWaterShader/blob/master/Assets/Shaders/ToonWater.shader sample

 

You don't need these branches. Generally, don't do branches in shaders until you really know what you're doing. Just do something like:

Code (csharp):

1.  
2. float snowMask = saturate(difference * surfaceNoiseSample * 10.0);
3. albedo = lerp(c.rgb, _SnowColor.rgb, snowMask);
4.  

 

Ok thanks. I'll try to refactor my code better because I just solved it by... putting noiseSample comparison in same IF

Code (CSharp):

1. if(difference >= _SnowLevel && surfaceNoiseSample >= _SnowLevel)
2. {
3.      albedo = _SnowColor.rgb;
4. }
5. else ...
6.  

 

Using saturate() was a incorrect solution because then snow loses the toony edge, some googling and found that step() is used for branching.

Code (CSharp):

1. float difference = dot(normal, _SnowDirection.xyz);
2. albedo =  lerp(_SnowColor.rgb, c.rgb, step(difference, 1 - _SnowLevel));

Also realized that my code was fine all along and the problem was the missing normal maps from material because didn't want any bumpiness in my objects but as a side effect the snow that is based on normal direction, well would need normal maps.

Lessons learned.