using UnityEngine;

// from https://wiki.unity3d.com/index.php/CameraGradientBackground
public class GradientBackground : MonoBehaviour {
    Camera _camera;
    public Shader shader;
    public Color topColor = Color.blue;
    public Color bottomColor = Color.white;
    public int gradientLayer = 7;
    public Transform attachPoint;

    void Awake() {
        _camera = GetComponent<Camera>();
        gradientLayer = Mathf.Clamp(gradientLayer, 0, 31);
        if (!_camera) {
            Debug.LogError("Must attach GradientBackground script to the camera");
            return;
        }

        _camera.clearFlags = CameraClearFlags.Depth;
        _camera.cullingMask = _camera.cullingMask & ~(1 << gradientLayer);
        Camera gradientCam = new GameObject("Gradient Cam", typeof(Camera)).GetComponent<Camera>();
        if (attachPoint != null)
            gradientCam.transform.SetParent(attachPoint);
        gradientCam.depth = _camera.depth - 1;
        gradientCam.cullingMask = 1 << gradientLayer;
        gradientCam.backgroundColor = Color.black;

        exprivia.ui.CameraIntoSafeArea.ResizeCameraIntoSafeArea(gradientCam);

        Mesh mesh = new Mesh();
        mesh.vertices = new Vector3[4]
                        {new Vector3(-100f, .577f, 1f), new Vector3(100f, .577f, 1f), new Vector3(-100f, -.577f, 1f), new Vector3(100f, -.577f, 1f)};
        //mesh.vertices = new Vector3[4]
        //                {new Vector3(-100f, .577f, 1f), new Vector3(100f, .577f, 1f), new Vector3(-100f, -.577f, 1f), new Vector3(100f, -.577f, 1f)};

        mesh.colors = new Color[4] { topColor, topColor, bottomColor, bottomColor };

        mesh.triangles = new int[6] { 0, 1, 2, 1, 3, 2 };

        Material mat = new Material(shader);
        GameObject gradientPlane = new GameObject("Gradient Plane", typeof(MeshFilter), typeof(MeshRenderer));
        if (attachPoint != null)
            gradientPlane.transform.SetParent(attachPoint);

        ((MeshFilter)gradientPlane.GetComponent(typeof(MeshFilter))).mesh = mesh;
        gradientPlane.GetComponent<Renderer>().material = mat;
        gradientPlane.layer = gradientLayer;
    }
}