Unity3d实现窗体透明效果

发表于2018-07-26

偶然在国外网站上看到的一个脚本，通过纯色背景抠像的方法，把windows的窗体透明化，可以用来做无背景的小头像、桌面精灵等。

首先新建一个叫TransparentWindow的CS脚本，输入如下代码：

using System;
using System.Runtime.InteropServices;
using UnityEngine;
public class TransparentWindow : MonoBehaviour
｛
    [SerializeField]
    private Material m_Material;
    private struct MARGINS
    ｛
        public int cxLeftWidth;
        public int cxRightWidth;
        public int cyTopHeight;
        public int cyBottomHeight;
    ｝
    // Define function signatures to import from Windows APIs
    [DllImport("user32.dll")]
    private static extern IntPtr GetActiveWindow();
    [DllImport("user32.dll")]
    private static extern int SetWindowLong(IntPtr hWnd, int nIndex, uint dwNewLong);
    [DllImport("Dwmapi.dll")]
    private static extern uint DwmExtendFrameIntoClientArea(IntPtr hWnd, ref MARGINS margins);
    // Definitions of window styles
    const int GWL_STYLE = -16;
    const uint WS_POPUP = 0x80000000;
    const uint WS_VISIBLE = 0x10000000;
    void Start()
    ｛
#if !UNITY_EDITOR
        var margins = new MARGINS() ｛ cxLeftWidth = -1 ｝;
        // Get a handle to the window
        var hwnd = GetActiveWindow();
        // Set properties of the window
        // See: https://msdn.microsoft.com/en-us/library/windows/desktop/ms633591%28v=vs.85%29.aspx
        SetWindowLong(hwnd, GWL_STYLE, WS_POPUP | WS_VISIBLE);
        // Extend the window into the client area
        //See: https://msdn.microsoft.com/en-us/library/windows/desktop/aa969512%28v=vs.85%29.aspx 
        DwmExtendFrameIntoClientArea(hwnd, ref margins);
#endif
    ｝
    // Pass the output of the camera to the custom material
    // for chroma replacement
    void OnRenderImage(RenderTexture from, RenderTexture to)
    ｛
        Graphics.Blit(from, to, m_Material);
    ｝
｝

然后新建一个叫ChromakeyTransparent的Shader：

Shader "Custom/ChromakeyTransparent" ｛
    Properties｛
        _MainTex("Base (RGB)", 2D) = "white" ｛｝
        _TransparentColourKey("Transparent Colour Key", Color) = (0,0,0,1)
        _TransparencyTolerance("Transparency Tolerance", Float) = 0.01
    ｝
    SubShader｛
        Pass｛
            Tags｛ "RenderType" = "Opaque" ｝
            LOD 200
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "UnityCG.cginc"
            struct a2v
            ｛
                float4 pos : POSITION;
                float2 uv : TEXCOORD0;
            ｝;
            struct v2f
            ｛
                float4 pos : SV_POSITION;
                float2 uv : TEXCOORD0;
            ｝;
            v2f vert(a2v input)
            ｛
                v2f output;
                output.pos = UnityObjectToClipPos(input.pos);
                output.uv = input.uv;
                return output;
            ｝
            sampler2D _MainTex;
            float3 _TransparentColourKey;
            float _TransparencyTolerance;
            float4 frag(v2f input) : SV_Target
            ｛
                // What is the colour that *would* be rendered here?
                float4 colour = tex2D(_MainTex, input.uv);
                // Calculate the different in each component from the chosen transparency colour
                float deltaR = abs(colour.r - _TransparentColourKey.r);
                float deltaG = abs(colour.g - _TransparentColourKey.g);
                float deltaB = abs(colour.b - _TransparentColourKey.b);
                // If colour is within tolerance, write a transparent pixel
                if (deltaR < _TransparencyTolerance && deltaG < _TransparencyTolerance && deltaB < _TransparencyTolerance)
                ｛
                    return float4(0.0f, 0.0f, 0.0f, 0.0f);
                ｝
                // Otherwise, return the regular colour
                return colour;
            ｝
            ENDCG
        ｝
    ｝
｝

新建一个材质，选择我们刚刚写好的Shader，将TransparentWindow挂载到摄像机上，摄像机的Clear Flags选择Solid Color，Background选择和材质的Transparent Color Key相同的颜色（建议选择与模型边缘颜色相近的颜色，不然会出现较明显的毛边），将材质拖拽给TransparentWindow的Material变量。