Unity&Shader案例篇-镜子1

    废话不多说先上效果图，我使用的是在Unity5.3.3版本。

一、原理
1、首先要准备的素材是三个，对没错，就是三个因为镜子里面的那个物体其实是实物的复制体而已；一个Plane作为镜子，还有一个实物和虚物体。
2、新建一个材质使用下面的Shader代码，并将此材质球赋给那个虚物体

Shader "Custom/Cg shader for virtual objects in mirrors" {
        Properties{
                _Color("Virtual Object's Color", Color) = (1, 1, 1, 1)
        }
                SubShader{
                Tags{ "Queue" = "Transparent+20" }

                Pass{
                Blend OneMinusDstAlpha DstAlpha

                CGPROGRAM

#pragma vertex vert 
#pragma fragment frag

#include "UnityCG.cginc"

                uniform float4 _Color;
        uniform float4x4 _WorldToMirror;

        struct vertexInput {
                float4 vertex : POSITION;
        };
        struct vertexOutput {
                float4 pos : SV_POSITION;
                float4 posInMirror : TEXCOORD0;
        };

        vertexOutput vert(vertexInput input)
        {
                vertexOutput output;

                output.posInMirror = mul(_WorldToMirror,
                        mul(_Object2World, input.vertex));
                output.pos = mul(UNITY_MATRIX_MVP, input.vertex);
                return output;
        }

        float4 frag(vertexOutput input) : COLOR
        {
                //如果镜子里的物体出来了就剔除掉
                if (input.posInMirror.y > 0.0)
                {
                        discard;
                }
        return float4(_Color.rgb, 0.0);
        }

                ENDCG
        }
        }
}

3、另外在建一个材质使用下面的Shader代码，并将此材质球赋值给实物体

Shader "Unlit/Cg shader for Real objects"
{
        Properties{
                _Color("Virtual Object's Color", Color) = (1, 1, 1, 1)
        }
   SubShader {
      Pass {
         CGPROGRAM

         #pragma vertex vert 
         #pragma fragment frag
                uniform float4 _Color;
         float4 vert(float4 vertexPos : POSITION) : SV_POSITION 
         {
            return mul(UNITY_MATRIX_MVP, vertexPos);
         }

         float4 frag(void) : COLOR
         {
            return float4(_Color.rgb, 1.0);
         }

         ENDCG
      }
   }
}

4、建立一个镜子的材质并将下面的Shader代码赋给作为镜子的那个面板

Shader "Unlit/Mirrors"
{
Properties{
_Color("Mirrors's Color", Color) = (1, 1, 1, 1)
}
SubShader{
Tags{ "Queue" = "Transparent+10" }
// draw after all other geometry has been drawn 
// because we mess with the depth buffer
//确保在所有的真实物体渲染之后再渲染

// 1st pass: mark mirror with alpha = 0
Pass{
CGPROGRAM

#pragma vertex vert 
#pragma fragment frag

float4 vert(float4 vertexPos : POSITION) : SV_POSITION
{
return mul(UNITY_MATRIX_MVP, vertexPos);
}

float4 frag(void) : COLOR
{
return float4(1.0, 0.0, 0.0, 0.0);
// this color should never be visible, 
// only alpha is important
}
ENDCG
}

// 2nd pass: set depth to far plane such that 
// we can use the normal depth test for the reflected geometry
Pass{
ZTest Always
Blend OneMinusDstAlpha DstAlpha
//==float4 result = float4(1.0 - pixel_color.a) * fragment_output + float4(pixel_color.a) * pixel_color;

CGPROGRAM

#pragma vertex vert 
#pragma fragment frag

uniform float4 _Color;
// user-specified background color in the mirror

float4 vert(float4 vertexPos : POSITION) : SV_POSITION
{
float4 pos = mul(UNITY_MATRIX_MVP, vertexPos);
pos.z = pos.w;
// the perspective division will divide pos.z 
// by pos.w; thus, the depth is 1.0, 
// which represents the far clipping plane
return pos;
}

float4 frag(void) : COLOR
{
return float4(_Color.rgb, 0.0);
// set alpha to 0.0 and 
// the color to the user-specified background color
}
ENDCG
}
}
}

5、最后新建一个C#脚本，代码如下，将此代码赋给虚物体，并将Plane和虚物体拖动赋值给里面的对应两个变量

using UnityEngine;
using System.Collections;

[ExecuteInEditMode]
public class PlacingTheVirtualObj : MonoBehaviour {

    public GameObject objectInFrontOfMirror;
    public GameObject mirrorPlane;

    // Use this for initialization
    void Start () {

    }

    // Update is called once per frame
    void Update() {
        if (null != mirrorPlane)
        {
            //这句话决定了镜子里的物体是否可见
            GetComponent<Renderer>().sharedMaterial.SetMatrix("_WorldToMirror",mirrorPlane.GetComponent<Renderer>().worldToLocalMatrix);
            if (null != objectInFrontOfMirror)
            {
                //将实物的颜色值赋给镜中的物体
                Color realColor = objectInFrontOfMirror.GetComponent<Renderer>().material.GetColor("_Color");
                GetComponent<Renderer>().material.SetColor("_Color", realColor);

                transform.position = objectInFrontOfMirror.transform.position;
                transform.rotation = objectInFrontOfMirror.transform.rotation;
                transform.localScale =
                   -objectInFrontOfMirror.transform.localScale;
                //new Vector3(0.0f, 1.0f, 0.0f)为表面的法线方向
                transform.RotateAround(objectInFrontOfMirror.transform.position,mirrorPlane.transform.TransformDirection( new Vector3(0.0f, 1.0f, 0.0f)), 180.0f);
              Vector3  positionInMirrorSpace  =
                   mirrorPlane.transform.InverseTransformPoint(objectInFrontOfMirror.transform.position);
                positionInMirrorSpace.y = -positionInMirrorSpace.y;
                transform.position = mirrorPlane.transform.TransformPoint(
                   positionInMirrorSpace);
            }
        }
    }
}

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