Color Ramp Replacement Maintaining Alpha

So I'm new to shaders, and not quite sure what I am doing.

I'm trying to take a sprite in grayscale, and then with a color ramp, pallet swap those colors for new colors.

I've taken a few solutions from around the forms and made them into this.

Code (CSharp):

1.  
2. Shader "ColourReplacement" {
3.     Properties {
4.         _MainTex ("Greyscale (R) Alpha (A)", 2D) = "white" {}
5.         _ColorRamp ("Colour Palette", 2D) = "gray" {}
6.         _Clear ("NoAlpha", 2D) = "clear" {}
7.     }
8.     SubShader {
9.                     Tags
10.         {
11.             "Queue"="Transparent"
12.             "IgnoreProjector"="True"
13.             "RenderType"="Transparent"
14.             "PreviewType"="Plane"
15.             "CanUseSpriteAtlas"="False"  
16.         }
17.         Pass {
18.             Name "ColorReplacement"
19.          
20.  
21.             CGPROGRAM
22.                 #pragma vertex vert
23.                 #pragma fragment frag
24.                 #pragma fragmentoption ARB_precision_hint_fastest
25.                 #include "UnityCG.cginc"
26.              
27.                 struct v2f
28.                 {
29.                     float4  pos : SV_POSITION;
30.                     float2  uv : TEXCOORD0;
31.                 };
32.                 v2f vert (appdata_tan v)
33.                 {
34.                     v2f o;
35.                     o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
36.                     o.uv = v.texcoord.xy;
37.                     return o;
38.                 }
39.              
40.                 sampler2D _MainTex;
41.                 sampler2D _ColorRamp;
42.                 sampler2D _Clear;
43.                 float4 frag(v2f i) : COLOR
44.                 {
45.                 // SURFACE COLOUR
46.                     float greyscale = tex2D(_MainTex, i.uv).r;
47.              
48.         // RESULT
49.                     float4 result;
50.                     result.a = tex2D(_MainTex, i.uv).a;
51.                     if (result.a < 0.5)
52.                          result.rgb = tex2D(_Clear, i.uv).rgb;
53.                    else
54.                          result.rgb = tex2D(_ColorRamp, float2(greyscale, 0.5)).rgb;
55.                     return result;
56.                 }
57.             ENDCG
58.         }
59.     }
60.     FallBack "Diffuse"
61. }
62.  

Now in all honesty I'm not quite sure what is going on here, but it is mostly working, but when it should be replacing areas with small alpha with a transparent texture, it is making it black. Basically not having the alpha be transparent.

I know there are some cheep solutions on the asset store, but just looking to learn what's going on here.
Thanks for any help.

 

Hey! In order for a shader to render things as transparent, you need to tell it which blend mode to use. For a basic transparent shader, you'll want to put a row with "Blend SrcAlpha OneMinusSrcAlpha" somewhere between "Pass { " and "CGPROGRAM". More on blend modes here http://docs.unity3d.com/Manual/SL-Blend.html. It's also usually a good idea to also tell the shader not to write to the depth buffer when it's transparent, that would be a row with "ZWrite Off" in the same area.

 

Nice, perfect. Working how I want right now. I thought it was something around there, but shaders don't make sense to me yet.
Thanks for the help.