Demo 30 - Picture in picture

Shader "Custom/PictureInPicture" {
    Properties {
        _MainTex ("Base (RGB)", 2D) = "white" {}
        _SecondaryTex ("Secondary Texture", 2D) = "white" {}
        _GreenThreshold ("GreenThreshold", Range(0, 1.0)) = 0
        _BlueThreshold ("BlueThreshold", Range(0, 1.0)) = 0
        _RedThreshold ("RedThreshold", Range(0, 1.0)) = 0
    }
    SubShader {
        Pass {
            Tags { "RenderType"="Opaque" }

            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "UnityCG.cginc"

            struct v2f {
                float4 pos : SV_POSITION;
                float2 uv1 : TEXCOORD0;
                float2 uv2 : TEXCOORD1;
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;
            sampler2D _SecondaryTex;
            float4 _SecondaryTex_ST;

            v2f vert(appdata_base v) {
                v2f o;
                o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
                o.uv1 = TRANSFORM_TEX(v.texcoord, _MainTex);
                o.uv2 = TRANSFORM_TEX(v.texcoord, _SecondaryTex);
                return o;
            }

            float _GreenThreshold;
            float _BlueThreshold;
            float _RedThreshold;

            fixed4 frag(v2f i) : COLOR {
                fixed4 col1 = tex2D(_MainTex, i.uv1);
                fixed4 col2 = tex2D(_SecondaryTex, i.uv2);
                fixed val = floor(1 - saturate(col1.r - _RedThreshold))
                * floor(1 - saturate(col1.b - _BlueThreshold))
                * saturate(col1.g + _GreenThreshold);
                return lerp(col1, col2, val);
            }

            ENDCG
        }
    }
    FallBack "Diffuse"
}