using UnityEngine;
using System.Collections;
using UnityStandardAssets.ImageEffects;

public class Downsample : MonoBehaviour
{
    [ExecuteInEditMode]

    //The generated render texture
    RenderTexture downsampleRenderTexture;

    //One or several cameras that capture the game scene
    public Camera[] renderSourceCameras;

    //How much to downsample with
    public float downsampleFactor = 0.5f;

    //For UI renders, override with a pre-generated render texture. This is not used for the main camera.
    public RenderTexture customRenderTexture;

    //Read from playerPrefs to get specified downsample factor
    PlayerPrefsManager playerPrefsManager;

    void Start()
    {
        //Force update if the setting changes at runtime
        playerPrefsManager = PlayerPrefsManager.Instance;
        playerPrefsManager.settingsChanged.AddListener(SettingChanged);

        //Take DPI into account, and downsample more for higher DPI. Ensure that the factor is never greater than 1 and never less than 0.1.
        float dpiFactor = Mathf.Clamp((100 / (Screen.dpi + 4)), 0.1f, 1f);

        //Downsample by player pref * dpi compensation
        downsampleFactor = playerPrefsManager.resolutions[playerPrefsManager.currentResolution] * dpiFactor;

        //Update render texture dimensions and settings
        UpdateRenderTexture();
    }

    //Only runs at start or when setting changes
    void UpdateRenderTexture()
    {
        //Create a new render texture, either with screen dimensions (for main camera) or with custom dimensions for UI rendertextures
        if (customRenderTexture == null)
            downsampleRenderTexture = new RenderTexture((int)((float)Screen.width * downsampleFactor), (int)((float)Screen.height * downsampleFactor), 24, RenderTextureFormat.DefaultHDR);
        else
            downsampleRenderTexture = new RenderTexture((int)((float)customRenderTexture.width * downsampleFactor), (int)((float)customRenderTexture.height * downsampleFactor), 24, RenderTextureFormat.DefaultHDR);

        //Turn of AA and mipmapping, and use point filtering for pixelated look
        downsampleRenderTexture.antiAliasing = 1;
        downsampleRenderTexture.useMipMap = false;
        downsampleRenderTexture.filterMode = FilterMode.Point;

        //Set the actual render texture for the cameras
        for (int i = 0; i < renderSourceCameras.Length; i++)
        {
            renderSourceCameras[i].targetTexture = downsampleRenderTexture;
        }

    }

    //When setting changes, force a texture change
    private void SettingChanged()
    {
        downsampleFactor = playerPrefsManager.resolutions[playerPrefsManager.currentResolution];
        UpdateRenderTexture();
    }

    //The actual render happens here. On each render, as long as the gameobject is active, set the target texture to the generated render texture, render the scene, and perform a blit
    void OnRenderImage(RenderTexture source, RenderTexture destination)
    {
        if (gameObject.activeSelf)
        {
            //Render each camera
            for (int i = 0; i < renderSourceCameras.Length; i++)
            {
                renderSourceCameras[i].Render();
            }

            //Blit
            Graphics.Blit(downsampleRenderTexture, destination);
        }

    }

   //After each render, discard contents
   void OnPostRender()
    {
        if(downsampleRenderTexture != null)
        {
            downsampleRenderTexture.DiscardContents();
        }
    }
}