Dynamically Paint A Texture - I'm halfway but stuck!

Hi Everyone,

I'm working on a thing where I have an object that paints surfaces.
The problem is I'm clueless with shaders - my code currently has a base texture and a paint texture.

- That configuration works fine.

But(!)
I would like to have a totally transparent object (ie no initial/base texture), that only shows the dynamic painted texture.

any ideas? (my shader code is below)

Thank you so much!

Images to better explain:




my shader:

Code (CSharp):

1.  
2.  
3. Shader "CA/Paint Surface" {
4.  
5.     Properties{
6.         _MainTex("Main Texture", 2D) = "white" {}
7.     _PaintMap("PaintMap", 2D) = "white" {} // texture to paint on
8.     }
9.  
10.         SubShader{
11.         Tags{ "RenderType" = "Opaque" "LightMode" = "ForwardBase" }
12.  
13.         Pass{
14.         Lighting Off
15.  
16.         CGPROGRAM
17.  
18. #pragma vertex vert
19. #pragma fragment frag
20.  
21.  
22. #include "UnityCG.cginc"
23. #include "AutoLight.cginc"
24.  
25.     struct v2f {
26.         float4 pos : SV_POSITION;
27.         float2 uv0 : TEXCOORD0;
28.         float2 uv1 : TEXCOORD1;
29.  
30.     };
31.  
32.     struct appdata {
33.         float4 vertex : POSITION;
34.         float2 texcoord : TEXCOORD0;
35.         float2 texcoord1 : TEXCOORD1;
36.  
37.     };
38.  
39.     sampler2D _PaintMap;
40.     sampler2D _MainTex;
41.     float4 _MainTex_ST;
42.     v2f vert(appdata v) {
43.         v2f o;
44.  
45.         o.pos = UnityObjectToClipPos(v.vertex);
46.         o.uv0 = TRANSFORM_TEX(v.texcoord, _MainTex);
47.  
48.         o.uv1 = v.texcoord1.xy * unity_LightmapST.xy + unity_LightmapST.zw;// lightmap uvs
49.  
50.         return o;
51.     }
52.  
53.     half4 frag(v2f o) : COLOR{
54.         half4 main_color = tex2D(_MainTex, o.uv0); // main texture
55.         half4 paint = (tex2D(_PaintMap, o.uv1)); // painted on texture
56.         main_color *= paint;
57.  
58.         return main_color;
59.     }
60.         ENDCG
61.     }
62.     }
63. }

 

Thank you for the pointers @Remy_Unity I've got it all fixed up now!

 

Hi John, I'm just getting started on a project with a similar use case. I'm also a shader newbie, would you mind expanding on the solution you used a little bit? Specifically, how did you tie the position (I assume) of the paintbrush object to the paintmap coordinates? Many thanks!

 

Hi!
My starting point was this excellent post:
https://www.patreon.com/posts/rendertexture-15961186

 

This is excellent, thank you! And thanks for the quick reply.