AtmosphericFog.cs

using UnityEngine;

[ExecuteInEditMode]
[RequireComponent(typeof(Camera))]
[AddComponentMenu("Image Effects/Rendering/Atmospheric Fog")]

public class AtmosphericFog : PostEffectsBase {
    private float CAMERA_NEAR = 0.5f;
    private float CAMERA_FAR = 50.0f;
    private float CAMERA_FOV = 60.0f;
    private float CAMERA_ASPECT_RATIO = 1.333333f;

    [SerializeField] private Transform _sun;
    [SerializeField] private float globalDensity = 1.0f;
    [SerializeField] private float _seaLevel = 0f;
    [SerializeField] private float heightScale = 0.001f;
    [SerializeField] private float auraPower = 8f;

    [SerializeField] private Color fogColor = Color.grey;
    [SerializeField] private Color sunColor = Color.grey;

    public Shader fogShader;
    private Material fogMaterial = null;

    public override void Start() {
        base.Start();

        if (!_sun) {
            _sun = ServiceLocator.Instance.Sun;
        }
    }

    public override bool CheckResources() {
        CheckSupport (true);

        fogMaterial = CheckShaderAndCreateMaterial (fogShader, fogMaterial);

        if(!isSupported)
            ReportAutoDisable ();

        return isSupported;
    }

    private void OnRenderImage (RenderTexture source, RenderTexture destination) {
        if (CheckResources() == false) {
            Graphics.Blit(source, destination);
            return;
        }

        CAMERA_NEAR = camera.nearClipPlane;
        CAMERA_FAR = camera.farClipPlane;
        CAMERA_FOV = camera.fieldOfView;
        CAMERA_ASPECT_RATIO = camera.aspect;

        Matrix4x4 frustumCorners = Matrix4x4.identity;

        float fovWHalf = CAMERA_FOV * 0.5f;

        Vector3 toRight = camera.transform.right * CAMERA_NEAR * Mathf.Tan (fovWHalf * Mathf.Deg2Rad) * CAMERA_ASPECT_RATIO;
        Vector3 toTop = camera.transform.up * CAMERA_NEAR * Mathf.Tan (fovWHalf * Mathf.Deg2Rad);

        Vector3 topLeft = (camera.transform.forward * CAMERA_NEAR - toRight + toTop);
        float CAMERA_SCALE = topLeft.magnitude * CAMERA_FAR/CAMERA_NEAR;

        topLeft.Normalize();
        topLeft *= CAMERA_SCALE;

        Vector3 topRight = (camera.transform.forward * CAMERA_NEAR + toRight + toTop);
        topRight.Normalize();
        topRight *= CAMERA_SCALE;

        Vector3 bottomRight = (camera.transform.forward * CAMERA_NEAR + toRight - toTop);
        bottomRight.Normalize();
        bottomRight *= CAMERA_SCALE;

        Vector3 bottomLeft = (camera.transform.forward * CAMERA_NEAR - toRight - toTop);
        bottomLeft.Normalize();
        bottomLeft *= CAMERA_SCALE;

        frustumCorners.SetRow (0, topLeft);
        frustumCorners.SetRow (1, topRight);
        frustumCorners.SetRow (2, bottomRight);
        frustumCorners.SetRow (3, bottomLeft);

        fogMaterial.SetMatrix ("_FrustumCornersWS", frustumCorners);
        fogMaterial.SetVector ("_CameraWS", camera.transform.position);
        fogMaterial.SetVector ("_SunDir", -_sun.forward);

        fogMaterial.SetFloat ("_GlobalDensity", globalDensity);
        fogMaterial.SetFloat("_SeaLevel", _seaLevel);
        fogMaterial.SetFloat("_HeightScale", heightScale);
        fogMaterial.SetFloat("_AuraPower", auraPower);
        fogMaterial.SetColor ("_FogColor", fogColor);
        fogMaterial.SetColor("_SunColor", sunColor);

        CustomGraphicsBlit (source, destination, fogMaterial);
    }

    private static void CustomGraphicsBlit(RenderTexture source, RenderTexture dest, Material fxMaterial) {
        RenderTexture.active = dest;

        fxMaterial.SetTexture("_MainTex", source);

        GL.PushMatrix();
        GL.LoadOrtho();

        fxMaterial.SetPass (0);

        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();
    }
}