介紹

Alpha測試：符合條件的像素顯示出來，不符合的丟掉

一、fixed function shader的透明通度測試

ShaderLab: Legacy Alpha Testing

語法

關閉Alpha測試

AlphaTest Off

渲染所有的像素（默認）或者…
2. 開啟Alpha測試

AlphaTest comparison AlphaValue

設置alpha測試，根據alpha值篩選符合條件的像素進行渲染

Comparison Alpha測試的比較命令

• Greater
  Only render pixels whose alpha is greater than AlphaValue.
• GEqual
  Only render pixels whose alpha is greater than or equal to AlphaValue.
• Less
  Only render pixels whose alpha value is less than AlphaValue.
• LEqual
  Only render pixels whose alpha value is less than or equal to from AlphaValue.
• Equal
  Only render pixels whose alpha value equals AlphaValue.
• NotEqual
  Only render pixels whose alpha value differs from AlphaValue.
• Always
  Render all pixels. This is functionally equivalent to AlphaTest Off.
• Never
  Don’t render any pixels.

開啟alpha測試，只渲染alpha值大于0.5的像素：

Shader "Hidden/alphatest" {Properties{_MainTex ("Texture", 2D) = "white" {}}SubShader{// No culling or depthCull Off ZWrite Off ZTest Always// alphatest// AlphaTest OffAlphaTest Greater 0.5Pass{SetTexture[_MainTex]}} }

二、可編程shader的透明度測試

ShaLab的AlphaTest命令在shader2.0中是不起作用的。
由于可編程shader會對紋理采樣，可以直接操作紋理的透明通道值，因此也不需要AlphaTest命令。而fixed function shader不會紋理采樣，只能依靠AlphaTest命令進行Alpha測試。

同樣，開啟alpha測試，只渲染alpha值大于0.5的像素：

Shader "Hidden/alphatest2" {Properties{_MainTex ("Texture", 2D) = "white" {}}SubShader{// No culling or depth//Cull Off ZWrite Off ZTest AlwaysBlend SrcAlpha OneMinusSrcAlphaPass{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;};v2f vert (appdata v){v2f o;o.vertex = UnityObjectToClipPos(v.vertex);o.uv = v.uv;return o;}sampler2D _MainTex;fixed4 frag (v2f i) : SV_Target{fixed4 col = tex2D(_MainTex, i.uv);if(col.a < 0.5 ){return fixed4(0,0,0,0);}else{return col;}return col;}ENDCG}} }

總結

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