GPU 上的 HSL 图像调整

GPU 上的 HSL 图像调整案例代码及实现

shader
Shader "Custom/HSLAdjustment" {
    Properties {
        _MainTex ("Texture", 2D) = "white" {}
        _HueShift ("Hue Shift", Range(-180, 180)) = 0
        _Saturation ("Saturation", Range(-1, 1)) = 0
        _Luminance ("Luminance", Range(-1, 1)) = 0
    }
 
    SubShader {
        Tags { "RenderType"="Opaque" }
        LOD 200
 
        CGPROGRAM
        #pragma surface surf Lambert
 
        sampler2D _MainTex;
        float _HueShift;
        float _Saturation;
        float _Luminance;
 
        struct Input {
            float2 uv_MainTex;
        };
 
        void surf (Input IN, inout SurfaceOutput o) {
            float4 tex = tex2D(_MainTex, IN.uv_MainTex);
            float3 hsl = rgb2hsl(tex.rgb);
 
            // 色相调整
            hsl.x += _HueShift / 360;
            hsl.x = frac(hsl.x);
 
            // 饱和度调整
            hsl.y += _Saturation;
            hsl.y = clamp(hsl.y, 0, 1);
 
            // 亮度调整
            hsl.z += _Luminance;
            hsl.z = clamp(hsl.z, 0, 1);
 
            float3 rgb = hsl2rgb(hsl);
            o.Albedo = rgb;
            o.Alpha = tex.a;
        }
 
        float3 rgb2hsl(float3 rgb) {
            float r = rgb.r;
            float g = rgb.g;
            float b = rgb.b;
 
            float maxVal = max(max(r, g), b);
            float minVal = min(min(r, g), b);
            float h, s, l;
 
            l = (maxVal + minVal) / 2;
 
            if (maxVal == minVal) {
                h = 0;
                s = 0;
            } else {
                float d = maxVal - minVal;
 
                s = l > 0.5 ? d / (2 - maxVal - minVal) : d / (maxVal + minVal);
 
                if (maxVal == r) {
                    h = (g - b) / d + (g < b ? 6 : 0);
                } else if (maxVal == g) {
                    h = (b - r) / d + 2;
                } else {
                    h = (r - g) / d + 4;
                }
 
                h /= 6;
            }
 
            return float3(h, s, l);
        }
 
        float3 hsl2rgb(float3 hsl) {
            float h = hsl.x;
            float s = hsl.y;
            float l = hsl.z;
 
            float r, g, b;
 
            if (s == 0) {
                r = l;
                g = l;
                b = l;
            } else {
                float q = l < 0.5 ? l * (1 + s) : l + s - l * s;
                float p = 2 * l - q;
 
                r = hue2rgb(p, q, h + 1/3);
                g = hue2rgb(p, q, h);
                b = hue2rgb(p, q, h - 1/3);
            }
 
            return float3(r, g, b);
        }
 
        float hue2rgb(float p, float q, float t) {
            if (t < 0) t += 1;
            if (t > 1) t -= 1;
            if (t < 1/6) return p + (q - p) * 6 * t;
            if (t < 1/2) return q;
            if (t < 2/3) return p + (q - p) * (2/3 - t) * 6;
            return p;
        }
 
        ENDCG
    }
}