目录
问题描述
中间是默认的UI贴图，因为unity勾选SRBG，不处理Alpha通道，所以可能出现在线性空间下贴图Alpha与Ps显示不一致
解决办法：
在UIShader中加入 alpha通道的 Gamma颜色空间到Linner空间的计算，
AESshader
去找到UI/Defailt的shader源码，找到自己版本的Shader,地址：
https://unity3d.com/get-unity/download/archive
添加GammaToLinearSpace转换,添加三句
完整Shader:
// Unity built-in shader source. Copyright (c) 2016 Unity Technologies. MIT license (see license.txt)
Shader "UI/GammaToLinner"
{
Properties
{
[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;
half4 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 = half4(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;
}
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
float3 temp_cast_2 = (color.a).xxx;
float3 gammaToLinear8 = GammaToLinearSpace(temp_cast_2);
color.a = gammaToLinear8;
color.rgb *= color.a;
return color;
}
ENDCG
}
}
}
经验公式
直接使用GammaToLinearSpace，会导致alpha在纯黑白混合情况出现问题，使用经验公式，效果更好
float whiteAlpha = pow(color.a, 2.2);
float blackAlpha = 1.0 - pow((1 - color.a), 2.2);
float lum = max(color.b, max(color.r, color.g));
color.a = lerp(blackAlpha, whiteAlpha, lum);
color.rgb *= color.a;
return color;最终效果对比：
此方法只能用于没有多个带Alpha图片叠加的情况，如果有叠加，会发现叠加Alpha之后的图片会偏亮，因为每个Shader 都做了GammaToLinner处理，导致结果不正确，多Alpha图片叠加情况，需要采用后处理，只进行一次GammaToLinner 操作
后处理方式GammaToLinner
推荐视频
https://www.bilibili.com/video/av38607808?from=search&seid=11710377273002903334
