Dissolving mesh with multiple materials attached

Hello!
I'm trying to figure out how to dissolve quad with multiple materials attached.
Quad used as base for 2d background with 3 materials - first for sky texture, second for clouds texture and third for foreground texture. All 3 materials uses custom modified shader made from Unlit/Transparent shader with added Color field to control texture color and alpha.

Code (CSharp):

1. Shader "Unlit/TransparentColor" {
2. Properties
3. {
4.     _MainTex ("Base (RGB) Trans (A)", 2D) = "white" {}
5.     _Color("Main Color", Color) = (1,1,1,1)
6. }
7.  
8. SubShader
9. {
10.     Tags
11.     {
12.         "Queue"="Transparent"
13.         "IgnoreProjector"="True"
14.         "RenderType"="Transparent"
15.         "PreviewType" = "Plane"
16.     }
17.     LOD 100
18.    
19.     Cull Off
20.     Lighting Off
21.     ZWrite Off
22.     Blend One OneMinusSrcAlpha
23.    
24.     Pass {
25.         CGPROGRAM
26.             #pragma vertex vert
27.             #pragma fragment frag
28.             #pragma target 2.0
29.             #pragma multi_compile_fog
30.            
31.             #include "UnityCG.cginc"
32.  
33.             struct appdata_t {
34.                 float4 vertex : POSITION;
35.                 float4 color    : COLOR;
36.                 float2 texcoord : TEXCOORD0;
37.                 UNITY_VERTEX_INPUT_INSTANCE_ID
38.             };
39.  
40.             struct v2f {
41.                 float4 vertex : SV_POSITION;
42.                 fixed4 color : COLOR;
43.                 float2 texcoord : TEXCOORD0;
44.                 UNITY_FOG_COORDS(1)
45.                 UNITY_VERTEX_OUTPUT_STEREO
46.             };
47.  
48.             fixed4 _Color;
49.             sampler2D _MainTex;
50.             float4 _MainTex_ST;
51.            
52.             v2f vert (appdata_t v)
53.             {
54.                 v2f o;
55.                 UNITY_SETUP_INSTANCE_ID(v);
56.                 UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o);
57.                 o.vertex = UnityObjectToClipPos(v.vertex);
58.                 o.texcoord = TRANSFORM_TEX(v.texcoord, _MainTex);
59.                 o.color = v.color * _Color;
60.                 UNITY_TRANSFER_FOG(o,o.vertex);
61.                 return o;
62.             }
63.            
64.             fixed4 frag (v2f i) : SV_Target
65.             {
66.                 fixed4 col = tex2D(_MainTex, i.texcoord) * i.color;
67.                 col.rgb *= col.a;
68.                 UNITY_APPLY_FOG(i.fogCoord, col);
69.                 return col;
70.             }
71.         ENDCG
72.     }
73. }
74.  
75. }

Clouds animated by changing clouds material UV in simple script.

Now the problem: I want to dissolve whole background with all materials and I'm trying to change materials alpha to achieve this with script but in process foreground became semi-transparent and I can see clouds through foreground.

Example: http://recordit.co/01WyWl09wn

Is there a way to dissolve this gameobject without clouds becoming visible through foreground while still animating clouds?

 

Yes, by using a single material & shader that can render all those layers at once.

Basically you want to make two duplicates of all lines with "_MainTex", replacing MainTex with SkyTex and CloudTex for example. Then composite them together with lerp() functions.