效果如下
?
原理：
????????倒影区域也用图片本体，做个镜像翻转（RectTransform中的scale的Y设为-1），然后shader对图片进行处理，达到一个透明度Y方向上渐变的效果。
实现：
????????因为是UGUI上使用，推荐直接在内置的UI-Default.shader中进行修改（官网可以下载）。
要达到Y方向上的透明度渐变，可以使用UV坐标中的v作为变化因子，通过一个衰减曲线达到效果，我这里采用的指数函数（Pow），关键代码其实就下面这一句，如下：
color.a *= pow(1 - IN.texcoord.y, _Pow);_Pow就是调节范围变化：
?
而整体透明度调整可以直接修改RawImage中的Color的Alpha即可（这里就直接修改的顶点颜色）。
完整代码：
Shader "Unlit/UIShadow"
{
Properties
{
[PerRendererData] _MainTex ("Sprite Texture", 2D) = "white" {}
[HideInInspector]_Color ("Tint", Color) = (1,1,1,1)
[HideInInspector]_StencilComp ("Stencil Comparison", Float) = 8
[HideInInspector]_Stencil ("Stencil ID", Float) = 0
[HideInInspector]_StencilOp ("Stencil Operation", Float) = 0
[HideInInspector]_StencilWriteMask ("Stencil Write Mask", Float) = 255
[HideInInspector]_StencilReadMask ("Stencil Read Mask", Float) = 255
[HideInInspector]_ColorMask ("Color Mask", Float) = 15
[HideInInspector][Toggle(UNITY_UI_ALPHACLIP)] _UseUIAlphaClip ("Use Alpha Clip", Float) = 0
_Pow("Pow",range(1,10)) = 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
{
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;
float _Pow;
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;
color.a *= pow(1 - IN.texcoord.y, _Pow);
#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
}
}
}
