问题描述：美术使用PS在Gamma空间下设计的UI图，导入到Unity，因为Unity使用的是线性空间，导致半透明的UI效果和美术设计的不一致。
解决方案：
（一）让美术在线性空间下工作
（二）在Unity里使用自定义Shader处理半透明UI
PS中Gamma空间计算公式：color = A.rgb*A.alpha + B.rgb*(1-A.alpha)
Unity为线性空间，图片不勾选sRGB，图片是Gamma空间的，思路就是转到Gamma空间下进行alpha混合，然后再转回线性空间返回结果。（shader可能有问题，先记录下来，后续再改）
// Unity built-in shader source. Copyright (c) 2016 Unity Technologies. MIT license (see license.txt)
Shader "UI/DefaultExt"
{
Properties
{
[Toggle(_True)] _IsGamma ("IsGamma", Float) = 1
[PerRendererData] _MainTex ("Sprite Texture", 2D) = "white" {}
_Color ("Tint", Color) = (1,1,1,1)
_StencilComp ("Stencil Comparison", Float) = 8
_Stencil ("Stencil ID", Float) = 0
_StencilOp ("Stencil Operation", Float) = 0
_StencilWriteMask ("Stencil Write Mask", Float) = 255
_StencilReadMask ("Stencil Read Mask", Float) = 255
_ColorMask ("Color Mask", Float) = 15
[Toggle(UNITY_UI_ALPHACLIP)] _UseUIAlphaClip ("Use Alpha Clip", Float) = 0
}
SubShader
{
Tags
{
"Queue"="Transparent"
"IgnoreProjector"="True"
"RenderType"="Transparent"
"PreviewType"="Plane"
"CanUseSpriteAtlas"="True"
}
Stencil
{
Ref [_Stencil]
Comp [_StencilComp]
Pass [_StencilOp]
ReadMask [_StencilReadMask]
WriteMask [_StencilWriteMask]
}
Cull Off
Lighting Off
ZWrite Off
ZTest [unity_GUIZTestMode]
Blend One OneMinusSrcAlpha
ColorMask [_ColorMask]
Pass
{
Name "Default"
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#pragma target 2.0
#include "UnityCG.cginc"
#include "UnityUI.cginc"
#pragma multi_compile_local _ UNITY_UI_CLIP_RECT
#pragma multi_compile_local _ UNITY_UI_ALPHACLIP
struct appdata_t
{
float4 vertex : POSITION;
float4 color : COLOR;
float2 texcoord : TEXCOORD0;
UNITY_VERTEX_INPUT_INSTANCE_ID
};
struct v2f
{
float4 vertex : SV_POSITION;
fixed4 color : COLOR;
float2 texcoord : TEXCOORD0;
float4 worldPosition : TEXCOORD1;
float4 mask : TEXCOORD2;
UNITY_VERTEX_OUTPUT_STEREO
};
sampler2D _MainTex;
fixed4 _Color;
fixed4 _TextureSampleAdd;
float4 _ClipRect;
float4 _MainTex_ST;
float _UIMaskSoftnessX;
float _UIMaskSoftnessY;
v2f vert(appdata_t v)
{
v2f OUT;
UNITY_SETUP_INSTANCE_ID(v);
UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(OUT);
float4 vPosition = UnityObjectToClipPos(v.vertex);
OUT.worldPosition = v.vertex;
OUT.vertex = vPosition;
float2 pixelSize = vPosition.w;
pixelSize /= float2(1, 1) * abs(mul((float2x2)UNITY_MATRIX_P, _ScreenParams.xy));
float4 clampedRect = clamp(_ClipRect, -2e10, 2e10);
float2 maskUV = (v.vertex.xy - clampedRect.xy) / (clampedRect.zw - clampedRect.xy);
OUT.texcoord = TRANSFORM_TEX(v.texcoord.xy, _MainTex);
OUT.mask = float4(v.vertex.xy * 2 - clampedRect.xy - clampedRect.zw, 0.25 / (0.25 * half2(_UIMaskSoftnessX, _UIMaskSoftnessY) + abs(pixelSize.xy)));
OUT.color = v.color * _Color;
return OUT;
}
// inline half3 GammaToLinearSpace (half3 sRGB)
// {
// // Approximate version from http://chilliant.blogspot.com.au/2012/08/srgb-approximations-for-hlsl.html?m=1
// return sRGB * (sRGB * (sRGB * 0.305306011h + 0.682171111h) + 0.012522878h); // Precise version, useful for debugging.
// //return half3(GammaToLinearSpaceExact(sRGB.r), GammaToLinearSpaceExact(sRGB.g), GammaToLinearSpaceExact(sRGB.b));
// }
half3 LinearToGammaSpace3(half3 col)
{
col.r = LinearToGammaSpaceExact(col.r);
col.g = LinearToGammaSpaceExact(col.g);
col.b = LinearToGammaSpaceExact(col.b);
return col;
}
half3 GammaToLinearSpace3(half3 col)
{
col.r = GammaToLinearSpaceExact(col.r);
col.g = GammaToLinearSpaceExact(col.g);
col.b = GammaToLinearSpaceExact(col.b);
return col;
}
float _IsGamma;
fixed4 frag(v2f IN) : SV_Target
{
//Round up the alpha color coming from the interpolator (to 1.0/256.0 steps)
//The incoming alpha could have numerical instability, which makes it very sensible to
//HDR color transparency blend, when it blends with the world's texture.
const half alphaPrecision = half(0xff);
const half invAlphaPrecision = half(1.0/alphaPrecision);
IN.color.a = round(IN.color.a * alphaPrecision)*invAlphaPrecision;
half4 color = IN.color * (tex2D(_MainTex, IN.texcoord) + _TextureSampleAdd);
#ifdef UNITY_UI_CLIP_RECT
half2 m = saturate((_ClipRect.zw - _ClipRect.xy - abs(IN.mask.xy)) * IN.mask.zw);
color.a *= m.x * m.y;
#endif
#ifdef UNITY_UI_ALPHACLIP
clip (color.a - 0.001);
#endif
color.rgb *= color.a;
if (_IsGamma != 1)
{
color.rgb = GammaToLinearSpace(color.rgb);
// color.rgb = GammaToLinearSpace3(color.rgb);
// color.a = pow(color.a, 0.45);
color.a = LinearToGammaSpaceExact(color.a);
}
return color;
}
ENDCG
}
}
}
参考：
Gamma、Linear、sRGB 和Unity Color Space，你真懂了吗？ - 知乎
unity gamma(伽马) linear(线性) 互转代码及问题处理_unity gamma转linear_Dawn·张的博客-CSDN博客
Unity线性空间UI的问题_unity 线性空间_zhjzhjxzhl的博客-CSDN博客
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