using System;
using UnityEngine;

[ExecuteAlways]
[AddComponentMenu("Image Effects/Blur/Blur")]
public class Blur : MonoBehaviour
{
    /// Blur iterations - larger number means more blur.
    [Range(0, 10)]
    public int iterations = 3;

    /// Blur spread for each iteration. Lower values
    /// give better looking blur, but require more iterations to
    /// get large blurs. Value is usually between 0.5 and 1.0.
    [Range(0.0f, 1.0f)]
    public float blurSpread = 0.6f;


    // --------------------------------------------------------
    // The blur iteration shader.
    // Basically it just takes 4 texture samples and averages them.
    // By applying it repeatedly and spreading out sample locations
    // we get a Gaussian blur approximation.

    public Shader blurShader {
        get { return Shader.Find("Hidden/BlurEffectConeTap"); }
    }

    static Material m_Material = null;
    protected Material material {
        get {
            if (m_Material == null)
            {
                m_Material = new Material(blurShader);
                m_Material.hideFlags = HideFlags.DontSave;
            }
            return m_Material;
        }
    }

    protected void Awake()
    {
        CameraUtility.RegisterBlur(this);
    }

    private void OnDestroy()
    {
        CameraUtility.UnRegisterBlur(this);
    }

    protected void OnDisable()
    {
        if (m_Material)
        {
            DestroyImmediate(m_Material);
        }
    }

    // --------------------------------------------------------

    protected void Start()
    {
        // Disable if we don't support image effects
        if (!SystemInfo.supportsImageEffects)
        {
            enabled = false;
            return;
        }
        // Disable if the shader can't run on the users graphics card
        if (!blurShader || !material.shader.isSupported)
        {
            enabled = false;
            return;
        }
    }

    // Performs one blur iteration.
    public void FourTapCone(RenderTexture source, RenderTexture dest, int iteration)
    {
        float off = 0.5f + iteration * blurSpread;
        Graphics.BlitMultiTap(source, dest, material,
                               new Vector2(-off, -off),
                               new Vector2(-off, off),
                               new Vector2(off, off),
                               new Vector2(off, -off)
            );
    }

    // Downsamples the texture to a quarter resolution.
    private void DownSample4x(RenderTexture source, RenderTexture dest)
    {
        float off = 1.0f;
        Graphics.BlitMultiTap(source, dest, material,
                               new Vector2(-off, -off),
                               new Vector2(-off, off),
                               new Vector2(off, off),
                               new Vector2(off, -off)
            );
    }

    // Called by the camera to apply the image effect
    void OnRenderImage(RenderTexture source, RenderTexture destination)
    {
        int rtW = source.width / 4;
        int rtH = source.height / 4;
        RenderTexture buffer = RenderTexture.GetTemporary(rtW, rtH, 0);

        // Copy source to the 4x4 smaller texture.
        DownSample4x(source, buffer);

        // Blur the small texture
        for (int i = 0; i < iterations; i++)
        {
            RenderTexture buffer2 = RenderTexture.GetTemporary(rtW, rtH, 0);
            FourTapCone(buffer, buffer2, i);
            RenderTexture.ReleaseTemporary(buffer);
            buffer = buffer2;
        }
        Graphics.Blit(buffer, destination);

        RenderTexture.ReleaseTemporary(buffer);
    }
}