基于视口坐标的Untiy渐变遮罩Shader

适用于位置大致静止的UI、精灵
项目里也在Live2d上得到了很好的效果

// Upgrade NOTE: replaced 'mul(UNITY_MATRIX_MVP,*)' with 'UnityObjectToClipPos(*)'

Shader "ImageEffect/MaskIcon"
{
    
    
	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

		_TransParentVPosLeft("TransParent Left View Port Pos",range(0,1)) = 0
		_TransParentVPosRight("TransParent Right View Port Pos",range(0,1)) = 1
		_TransParentWidth("TransparentWidth",Float)=0.1


		_TransParentVPosUp("TransParent Up View Port Pos",range(0,1)) = 1
		_TransParentVPosDown("TransParent Down View Port Pos",range(0,1)) = 0

		_TransParentHeight("TransparentHeight",Float) = 0.1
	}

		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_CLIP_RECT
#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
	};

	sampler2D _MainTex;
	fixed4 _Color;
	fixed4 _TextureSampleAdd;
	float4 _ClipRect;
	float4 _MainTex_ST;

	half _TransParentVPosLeft;
	half _TransParentVPosRight;	
	half _TransParentVPosUp;
	half _TransParentVPosDown;
	half _TransParentWidth;
	half _TransParentHeight;
	v2f vert(appdata_t v)
	{
    
    
		v2f OUT;
		UNITY_SETUP_INSTANCE_ID(v);
		UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(OUT);
		OUT.worldPosition = v.vertex;
		OUT.vertex = UnityObjectToClipPos(OUT.worldPosition);

		OUT.texcoord = TRANSFORM_TEX(v.texcoord, _MainTex);

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

	fixed4 frag(v2f IN) : SV_Target
	{
    
    
		half4 color = (tex2D(_MainTex, IN.texcoord) + _TextureSampleAdd) * IN.color;
		half vposx = IN.vertex.x / _ScreenParams.x;
		half vposy = IN.vertex.y / _ScreenParams.y;
		//min(左右渐变透明度，上下渐变透明度
		//是否渐变=判断点是否在left 和 right 之间 
		//透明度判断 是在左边 还是右边  然后乘上(_TransParentVPosRight - vposx) / _TransParentWidth)  这个懂吧
		//上下同理
		color.a *=
			min(clamp(step(_TransParentVPosLeft, vposx)*step(vposx, _TransParentVPosRight)
				*(step(vposx, _TransParentVPosRight - _TransParentWidth)*(vposx - _TransParentVPosLeft) / _TransParentWidth
					+ step(_TransParentVPosLeft + _TransParentWidth, vposx)*(_TransParentVPosRight - vposx) / _TransParentWidth), 0, 1)
				, clamp(step(_TransParentVPosDown, vposy)*step(vposy, _TransParentVPosUp)
					*(step(vposy, _TransParentVPosUp - _TransParentHeight)*(vposy - _TransParentVPosDown) / _TransParentHeight
						+ step(_TransParentVPosDown + _TransParentHeight, vposy)*(_TransParentVPosUp - vposy) / _TransParentHeight), 0, 1))
			;

#ifdef UNITY_UI_CLIP_RECT
		color.a *= UnityGet2DClipping(IN.worldPosition.xy, _ClipRect);
#endif

#ifdef UNITY_UI_ALPHACLIP
		clip(color.a - 0.001);
#endif

			return color;
	}
		ENDCG
	}
	}
}