1.代码

Shader "Custom/FishEye"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _DistortionAmount ("Distortion Amount", Range(0, 1)) = 0.5
    }
    SubShader
    {
        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD0;
            };

            struct v2f
            {
                float2 uv : TEXCOORD0;
                float4 vertex : SV_POSITION;
            };

            sampler2D _MainTex;
            float _DistortionAmount;

            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = v.uv;
                return o;
            }

            float2 FishEyeDistortion(float2 uv, float amount)
            {
                float2 center = float2(0.5, 0.5);
                float2 delta = uv - center;
                float dist = length(delta);
                float factor = pow(dist, amount);
                return center + delta * factor;
            }

            fixed4 frag (v2f i) : SV_Target
            {
                // Apply the distortion
                float2 distortedUv = FishEyeDistortion(i.uv, _DistortionAmount);

                // Sample the texture
                fixed4 col = tex2D(_MainTex, distortedUv);

                return col;
            }
            ENDCG
        }
    }
}

效果:

2.参数方程实现

Shader "Custom/FishEye"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _DistortionFactor ("Distortion Factor", Range(-2, 2)) = 0.5
    }
    SubShader
    {
        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD0;
            };

            struct v2f
            {
                float2 uv : TEXCOORD0;
                float4 vertex : SV_POSITION;
            };

            sampler2D _MainTex;
            float _DistortionFactor;

            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = v.uv;
                return o;
            }

            float2 DistortCoordinates(float2 uv, float factor)
            {
                float2 center = float2(0.5, 0.5);
                uv -= center;
                float r = length(uv);
                float theta = atan2(uv.y, uv.x);

                // Apply the distortion equation
                float rDistorted = r * (1.0 - factor * r * r);

                // Convert back to Cartesian coordinates
                return float2(rDistorted * cos(theta), rDistorted * sin(theta)) + center;
            }

            fixed4 frag (v2f i) : SV_Target
            {
                // Apply the distortion
                float2 distortedUv = DistortCoordinates(i.uv, _DistortionFactor);

                // Sample the texture
                fixed4 col = tex2D(_MainTex, distortedUv);

                return col;
            }
            ENDCG
        }
    }
}

效果: