之前有人做过,不过效率不高: http://blog.csdn.net/onerain88/article/details/12197277
他的代码:
{
fixed4 col;
if (i.color.r < 0.001)
{
col = tex2D(_MainTex, i.texcoord);
float grey = dot(col.rgb, float3(0.299, 0.587, 0.114));
col.rgb = float3(grey, grey, grey);
}
else
{
col = tex2D(_MainTex, i.texcoord) * i.color;
}
return col;
}
通过修改后效率明显大幅提升:
Shader "Unlit/Transparent Colored Gray"
{
Properties
{
_MainTex ("Base (RGB) Gray, Alpha (A)", 2D) = "white" {}
}
SubShader
{
LOD 100
Tags
{
"Queue" = "Transparent"
"IgnoreProjector" = "True"
"RenderType" = "Transparent"
}
Pass
{
Cull Off
Lighting Off
ZWrite Off
Fog { Mode Off }
Offset -1, -1
ColorMask RGB
AlphaTest Greater .01
Blend SrcAlpha OneMinusSrcAlpha
ColorMaterial AmbientAndDiffuse
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#pragma fragmentoption ARB_precision_hint_fastest
#include "UnityCG.cginc"
sampler2D _MainTex;
fixed4 _Color;
struct appdata_t
{
float4 vertex : POSITION;
fixed4 color : COLOR;
float2 texcoord : TEXCOORD0;
};
struct v2f
{
float4 vertex : POSITION;
fixed4 color : COLOR;
float2 texcoord : TEXCOORD0;
fixed gray : TEXCOORD1;
};
float4 _MainTex_ST;
v2f vert (appdata_t v)
{
v2f o;
o.vertex = mul(UNITY_MATRIX_MVP, v.vertex);
o.color = v.color;
o.gray = dot(v.color, fixed4(1,1,1,0));
o.texcoord = TRANSFORM_TEX(v.texcoord, _MainTex);
return o;
}
fixed4 frag (v2f i) : COLOR
{
fixed4 col;
if (i.gray == 0)
{
col = tex2D(_MainTex, i.texcoord);
col.rgb = dot(col.rgb, fixed3(.222,.707,.071));
}
else
{
col = tex2D(_MainTex, i.texcoord) * i.color;
}
return col;
}
ENDCG
}
}
}
![](https://images0.cnblogs.com/blog/694368/201411/291356559819599.jpg)
原理是在v2f中申请一个寄存器TEXCOORD1放置数据gray,并在顶点程序vert中计算是否灰色,在片段程序frag中用i.gray == 0做if判断。
第一段代码效率低的原因是if (i.color.r < 0.001)这里访问了color的分量r,但在官方文档中明确说了这样做效率低,除非必要情况时才使用。
另外在PC中(fixed gray : TEXCOORD1;)可以改成(bool gray : TEXCOORD1;),但在移动设备(android和ios)中都会有问题,求解。