using UnityEngine;
using UnityEngine.Rendering;
using System.Collections;

[ImageEffectAllowedInSceneView]
[ExecuteInEditMode, RequireComponent(typeof(Camera))]
public class ScreenTexture : MonoBehaviour
{
    public string textureSemanticName = "_GlobalScreenTexture";

#if UNITY_EDITOR
    public bool reset;
#endif

    private RenderTexture screenRenderTexture;
    private CommandBuffer commandBuffer;
    private Camera cameraComponent;


    void OnEnable()
    {
        cameraComponent = GetComponent<Camera>();
        SetupCommandBuffer();
    }

    void OnDisable()
    {

        cameraComponent.RemoveCommandBuffer(CameraEvent.BeforeForwardAlpha, commandBuffer);

#if UNITY_EDITOR
        if (UnityEditor.SceneView.currentDrawingSceneView != null && UnityEditor.SceneView.currentDrawingSceneView.camera != null)
        {
            UnityEditor.SceneView.currentDrawingSceneView.camera.RemoveCommandBuffer(CameraEvent.BeforeForwardAlpha, commandBuffer);
        }
#endif

        ReleaseCommandBuffer();
    }

    void SetupCommandBuffer()
    {
        commandBuffer = new CommandBuffer();
        cameraComponent.AddCommandBuffer(CameraEvent.BeforeForwardAlpha, commandBuffer);

        //old version, fine for getting screen texture but doesn't preserve opaque alpha
        //commandBuffer.SetGlobalTexture(textureSemanticName, BuiltinRenderTextureType.CurrentActive);
        // commandBuffer.SetGlobalTexture("_GlobalStencil", BuiltinRenderTextureType.CurrentActive);
        // cameraComponent.AddCommandBuffer(CameraEvent., commandBuffer);

        // copy screen into temporary RT - this stops transparent effects interfering with the alpha buffer
        var screenCopyID = Shader.PropertyToID("_GrabTexture");
        commandBuffer.GetTemporaryRT(screenCopyID, Screen.width, Screen.height, 0, FilterMode.Bilinear, RenderTextureFormat.ARGB32, RenderTextureReadWrite.Linear, QualitySettings.antiAliasing > 0 ? QualitySettings.antiAliasing : 1);//-1 gets full screen size RTs | -2 get half screen | -4 screen  / 4
        commandBuffer.Blit(BuiltinRenderTextureType.CurrentActive, screenCopyID);
        commandBuffer.SetGlobalTexture(textureSemanticName, screenCopyID);
        commandBuffer.ReleaseTemporaryRT(screenCopyID);

//make the effect work with editor mode
#if UNITY_EDITOR
        if (UnityEditor.SceneView.currentDrawingSceneView != null && UnityEditor.SceneView.currentDrawingSceneView.camera != null)
        {
            UnityEditor.SceneView.currentDrawingSceneView.camera.AddCommandBuffer(CameraEvent.BeforeForwardAlpha, commandBuffer);
        }
#endif

    }

    void Update()
    {
#if UNITY_EDITOR
        if (reset)
        {
            OnDisable();
            OnEnable();
            reset = false;
        }
#endif
    }

    void ReleaseCommandBuffer()
    {
        commandBuffer.Clear();
    }
}