unity 内置渲染管线URP写个平面反射的shader

### 如何在 Unity URP 中创建平面反射 Shader #### 创建着色器文件 为了实现在Unity Universal Render Pipeline (URP)中的平面反射效果，需要先定义一个自定义的Shader文件。这个Shader应该能够接收来自场景的信息，并基于这些信息计算出正确的反射。 ```hlsl Shader "Custom/PlaneReflection" { Properties { _MainTex ("Texture", 2D) = "white" {} _ReflectColor ("Reflection Color", Color) = (1,1,1,0.5) } SubShader { Tags { "RenderType"="Opaque" } Pass { Name "ForwardLit" HLSLPROGRAM #pragma vertex vert #pragma fragment frag struct Attributes { float4 positionOS : POSITION; float3 normalOS : NORMAL; float2 uv : TEXCOORD0; }; struct Varyings { float4 posHCS : SV_POSITION; float3 viewDirWS : TEXCOORD0; float3 worldPos : TEXCOORD1; float3 normalWS : TEXCOORD2; float2 uv : TEXCOORD3; }; sampler2D _CameraReflectionTexture; float4 _CameraReflectionTexture_ST; CBUFFER_START(UnityPerMaterial) float4 _MainTex_TexelSize; half4 _ReflectColor; CBUFFER_END TEXTURE2D(_MainTex); SAMPLER(sampler_MainTex); Varyings vert(Attributes input) { Varyings output; VertexPositionInputs vertexInput = GetVertexPositionInputs(input.positionOS.xyz); output.posHCS = vertexInput.positionCS; output.worldPos = mul(GetObjectToWorldMatrix(), float4(input.positionOS.xyz, 1)).xyz; output.normalWS = TransformObjectToWorldNormal(input.normalOS); output.viewDirWS = normalize(WorldSpaceViewDir(output.worldPos)); output.uv = TRANSFORM_TEX(input.uv, _MainTex); return output; } half4 frag(Varyings input) : SV_Target { // 计算反射方向 float3 reflectDir = reflect(-input.viewDirWS, input.normalWS); // 将反射方向转换到屏幕空间坐标系中 float4 clipSpaceReflectedRay = mul(UNITY_MATRIX_VP, float4(reflectDir, 0)); // 获取反射纹理坐标的偏移量 float2 screenUV = input.worldPos.xy * (_ScreenParams.zw - 1.0f) + 0.5f; float2 reflectionOffset = clipSpaceReflectedRay.xy / clipSpaceReflectedRay.w * 0.5f + 0.5f; float2 finalUV = screenUV + reflectionOffset; // 折射处理防止超出边界 finalUV = saturate(finalUV); // 采样反射贴图并应用颜色混合 half4 col = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, input.uv); half4 reflCol = SAMPLE_TEXTURE2D(_CameraReflectionTexture, sampler_CameraReflectionTexture, finalUV); return lerp(col, reflCol * _ReflectColor.a, _ReflectColor.rgb); } ENDHLSL } } } ``` 上述代码片段展示了如何构建一个基本的平面反射Shader[^1]。注意这里假设已经有一个名为`_CameraReflectionTexture`的纹理作为输入参数传递给Shader程序；这通常通过脚本来完成配置。 #### 编写 C# 脚本以支持反射功能 为了让上面编写的Shader正常工作，还需要编写一段C#脚本来管理摄像机捕捉以及提供必要的数据给Shader使用： ```csharp using UnityEngine; using UnityEngine.Rendering.Universal; public class PlaneReflectionManager : MonoBehaviour { public Camera mainCam; private RenderTexture reflectionRT; void OnEnable() { var volumeStack = VolumeManager.instance.stack; if (!mainCam.GetComponent<UniversalAdditionalCameraData>().renderingLayerMask.HasFlag(RenderingLayer.Reflection)) { Debug.LogError("The camera must have the 'Reflection' layer enabled."); return; } CreateReflectionTexture(); } void Update() { if (reflectionRT != null && !reflectionRT.IsCreated()) { DestroyImmediate(reflectionRT); CreateReflectionTexture(); } } void LateUpdate() { if(mainCam == null || reflectionRT == null) return; Graphics.Blit(null, reflectionRT, mainCam); } void CreateReflectionTexture() { int resWidth = Screen.width >> 1; int resHeight = Screen.height >> 1; reflectionRT = new RenderTexture(resWidth, resHeight, 24, RenderTextureFormat.ARGBHalf); reflectionRT.enableRandomWrite = true; reflectionRT.Create(); Shader.SetGlobalTexture("_CameraReflectionTexture", reflectionRT); } private void OnDestroy() { if (reflectionRT != null) { DestroyImmediate(reflectionRT); } } } ``` 这段脚本负责初始化和更新用于存储反射图像的`RenderTexture`对象，并将其设置为全局材质属性以便于Shader访问[^2]。