玻璃透明效果

2017-01-05

用ComputeGrabScreenPos取得被抓取的屏幕的对应对标。
计算出切线空间到世界坐标的转换矩阵，存在3个float4中，剩下的一位存入worldPos。
用_Distortion和_RefractionTex_TexelSize来计算出一个偏移量来偏移屏幕采样坐标，模拟折射的效果。
用反射方向对Cubemap采样，得到反射颜色，反射颜色+折射颜色得到最后的输出颜色。

Shader "UnityShaderLearning/GlassRefraction"
{
    Properties
    {
        _MainTex ("Main Tex", 2D) = "white" {}
        _BumpMap ("Normal Map", 2D) = "bump" {}
        _Cubemap ("Environment Cubemap", Cube) = "_Skybox" {}
        _Distortion ("Distortion", Range(0, 100)) = 10
        _RefractAmount ("Refract Amount", Range(0.0, 1.0)) = 1.0
    }
    SubShader
    {
        Tags { "Queue"="Transparent" "RenderType"="Opaque" }
        GrabPass { "_RefractionTex" }

        Pass
        {        
            CGPROGRAM

            #pragma vertex vert
            #pragma fragment frag

            #include "UnityCG.cginc"

            sampler2D _MainTex;
            float4 _MainTex_ST;
            sampler2D _BumpMap;
            float4 _BumpMap_ST;
            samplerCUBE _Cubemap;
            float _Distortion;
            fixed _RefractAmount;
            sampler2D _RefractionTex;
            float4 _RefractionTex_TexelSize;

            struct a2v
            {
                float4 vertex : POSITION;
                float2 texcoord : TEXCOORD0;
                float3 normal : NORMAL;
                float4 tangent : TANGENT;
            };

            struct v2f
            {
                float4 pos : SV_POSITION;
                float4 scrPos : TEXCOORD0;
                float4 uv : TEXCOORD1;
                float4 TtoW0 : TEXCOORD2;  
                float4 TtoW1 : TEXCOORD3;  
                float4 TtoW2 : TEXCOORD4; 
            };

            v2f vert (a2v v)
            {
                v2f o;
                o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
                o.scrPos = ComputeGrabScreenPos(o.pos);

                o.uv.xy = TRANSFORM_TEX(v.texcoord, _MainTex);
                o.uv.zw = TRANSFORM_TEX(v.texcoord, _BumpMap);

                float3 worldPos = mul(_Object2World, v.vertex).xyz;
                fixed3 worldNormal = UnityObjectToWorldNormal(v.normal);
                fixed3 worldTangent = UnityObjectToWorldDir(v.tangent.xyz);
                fixed3 worldBinormal = cross(worldNormal, worldTangent) * v.tangent.w;

                o.TtoW0 = float4(worldTangent.x, worldBinormal.x, worldNormal.x, worldPos.x);
                o.TtoW1 = float4(worldTangent.y, worldBinormal.y, worldNormal.y, worldPos.y);
                o.TtoW2 = float4(worldTangent.z, worldBinormal.z, worldNormal.z, worldPos.z);
                return o;
            }

            fixed4 frag(v2f i) : SV_Target
            {
                float3 worldPos = float3(i.TtoW0.w, i.TtoW1.w, i.TtoW2.w);
                fixed3 worldViewDir = normalize(UnityWorldSpaceViewDir(worldPos));
                fixed3 bump = UnpackNormal(tex2D(_BumpMap, i.uv.zw));
                float2 offset = bump.xy * _Distortion * _RefractionTex_TexelSize.xy;
                i.scrPos.xy = offset + i.scrPos.xy;
                fixed3 RefrCol = tex2D(_RefractionTex, i.scrPos.xy/i.scrPos.w).rgb;
                bump = normalize(half3(dot(i.TtoW0.xyz, bump), dot(i.TtoW1.xyz, bump), dot(i.TtoW2.xyz, bump)));
                fixed3 reflDir = reflect(-worldViewDir, bump);
                fixed4 texColor = tex2D(_MainTex, i.uv.xy);
                fixed3 reflCol = texCUBE(_Cubemap, reflDir).rgb * texColor.rgb;
                fixed3 finalColor = reflCol * (1 - _RefractAmount) + RefrCol * _RefractAmount;
                return fixed4(finalColor, 1);
            }
            ENDCG
        }
    }
    FallBack "Diffuse"
}