最近要寫新手引導，記錄一下

1<效果圖>

上面四張圖已經展示得很清楚了 shader裏面的計算也很簡單 對比了一下uv與中心點的位置關系

<2>源碼

Shader "Tang/matMask"
{
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
//除以2
_Origin("圓心",Vector) = (0.3,0.2,0,0)
_Height("高",Float) = 0.12
_Width("寬",Float) = 0.12

[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 SrcAlpha 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 __ 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;
UNITY_VERTEX_OUTPUT_STEREO
};

fixed4 _Color;
fixed4 _TextureSampleAdd;
float4 _ClipRect;
float4 _Origin;
float _Height;
float _Width;

v2f vert(appdata_t IN)
{
v2f OUT;
UNITY_SETUP_INSTANCE_ID(IN);
UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(OUT);
OUT.worldPosition = IN.vertex;
OUT.vertex = UnityObjectToClipPos(OUT.worldPosition);

OUT.texcoord = IN.texcoord;

OUT.color = IN.color * _Color;
return OUT;
}

sampler2D _MainTex;

fixed4 frag(v2f IN) : SV_Target
{
float2 uv = IN.texcoord;
half4 col = IN.color;
//開始裁剪
//外部直接給坐標 寬 高 GPU計算比率
float posX = (_Origin.x + 640) / 1280;
float posY = (_Origin.y + 360) / 720;
float w = _Origin.z / 1280 / 2;
float h = _Origin.w / 720 / 2;

float2 pos = float2(posX,posY);

if (uv.x > pos.x - w && uv.x<pos.x + w && uv.y>pos.y - h && uv.y < pos.y + h)
col.a = 0;

half4 color = (tex2D(_MainTex,uv) + _TextureSampleAdd) * col;

color.a *= UnityGet2DClipping(IN.worldPosition.xy, _ClipRect);
clip(col.a);
#ifdef UNITY_UI_ALPHACLIP
clip(color.a - 0.001);
#endif

return color;
}
ENDCG
}
}
}

[Shader]新手引導中的遮罩裁剪