Unity Shader：在Unity中使用GlobalFog
发表于2018-03-20
全局雾 (globalfog) 图像效果可创建基于相机的指数雾，而Unity自带的 GlobalFog 通过一个屏幕特效实现了全局雾效，本篇文章就基于此给大家介绍下在Unity中使用GlobalFog。
Camera cam = GetComponent<Camera>(); Transform camtr = cam.transform; float camNear = cam.nearClipPlane; float camFar = cam.farClipPlane; float camFov = cam.fieldOfView; float camAspect = cam.aspect; Matrix4x4 frustumCorners = Matrix4x4.identity; float fovWHalf = camFov * 0.5f; Vector3 toRight = camtr.right * camNear * Mathf.Tan (fovWHalf * Mathf.Deg2Rad) * camAspect; Vector3 toTop = camtr.up * camNear * Mathf.Tan (fovWHalf * Mathf.Deg2Rad); Vector3 topLeft = (camtr.forward * camNear - toRight + toTop); float camScale = topLeft.magnitude * camFar/camNear; topLeft.Normalize(); topLeft *= camScale; Vector3 topRight = (camtr.forward * camNear + toRight + toTop); topRight.Normalize(); topRight *= camScale; Vector3 bottomRight = (camtr.forward * camNear + toRight - toTop); bottomRight.Normalize(); bottomRight *= camScale; Vector3 bottomLeft = (camtr.forward * camNear - toRight - toTop); bottomLeft.Normalize(); bottomLeft *= camScale; frustumCorners.SetRow (0, topLeft); frustumCorners.SetRow (1, topRight); frustumCorners.SetRow (2, bottomRight); frustumCorners.SetRow (3, bottomLeft);
首先 Unity 通过上面一大堆代码算出了相机在远截面的四个角的位置，实际上用下面的函数可以代替：
Vector3[] corners = new Vector3[4]; cam.CalculateFrustumCorners(new Rect(0, 0, 1, 1),cam.farClipPlane , Camera.MonoOrStereoscopicEye.Mono, corners);
接下来的 CustomGraphicsBlit 函数就是核心所在
static void CustomGraphicsBlit (RenderTexture source, RenderTexture dest, Material fxMaterial, int passNr)
｛
RenderTexture.active = dest;
fxMaterial.SetTexture ("_MainTex", source);
GL.PushMatrix ();
GL.LoadOrtho ();
fxMaterial.SetPass (passNr);
GL.Begin (GL.QUADS);
GL.MultiTexCoord2 (0, 0.0f, 0.0f);
GL.Vertex3 (0.0f, 0.0f, 3.0f); // BL
GL.MultiTexCoord2 (0, 1.0f, 0.0f);
GL.Vertex3 (1.0f, 0.0f, 2.0f); // BR
GL.MultiTexCoord2 (0, 1.0f, 1.0f);
GL.Vertex3 (1.0f, 1.0f, 1.0f); // TR
GL.MultiTexCoord2 (0, 0.0f, 1.0f);
GL.Vertex3 (0.0f, 1.0f, 0.0f); // TL
GL.End ();
GL.PopMatrix ();
｝利用 GL 库绘制了一个四边形，在 XY 平面，四边形刚好覆盖整个屏幕，Z 坐标则对应了 frustumCorners 矩阵中的行，并在 vertex shader 中赋值
o.interpolatedRay = _FrustumCornersWS[(int)index]; o.interpolatedRay.w = index;
于是，经过光栅化的插值以后 interpolatedRay 则是由相机出发射向远截面的每一像素的向量，乘上深度纹理的值后，通过脚本传入的相机世界坐标，便可得到屏幕上每个像素点的世界坐标
float rawDepth = SAMPLE_DEPTH_TEXTURE(_CameraDepthTexture, UnityStereoTransformScreenSpaceTex(i.uv_depth)); float dpth = Linear01Depth(rawDepth); float4 wsDir = dpth * i.interpolatedRay; float4 wsPos = _CameraWS + wsDir;
至此，该有的条件都有了，便可以计算雾了，距离雾的计算较为简单，高度雾的计算则完全采用了 论文中的方法，连变量名都没改。
2、修改
根据论文的计算方法，在高度计算中加入了噪声，这里就没有考虑效率了，并且只是简单的将原本高度替换为交电处的噪声采样高度
//custom
if(FdotC * FdotP < 0.0)
｛
float x = FdotC/V.y * V.x;
float z = FdotC/V.y * V.z;
float2 spos = C.xz + float2(x,z);
spos *= 0.1;
float NH = tex2D(_NoiseTex, spos + float2(_Time.x,0.0)).r * _NoiseScale;
float differ = NH - FH;
FdotC += differ;
FdotP += differ;
if(FdotC <= 0.0)
k = 1.0;
else
k = 0.0;
｝效果如下：
同样的在距离雾中加入了噪声
float3 wpos = camDir/dist; float ND = tex2D(_NoiseTex, wpos.xy + float2(_Time.x,0.0)).r; dist -= pow(ND,5) * _NoiseScaleDis; return max(dist,0.0);
效果如下：
两者一起效果如下：
3、天空盒 Blend
改进的全局雾效果