using UnityEngine;

// This class implements simple ghosting type Motion Blur.
// If Extra Blur is selected, the scene will allways be a little blurred,
// as it is scaled to a smaller resolution.
// The effect works by accumulating the previous frames in an accumulation
// texture.
[ExecuteInEditMode]
[AddComponentMenu("Image Effects/Blur/Motion Blur (Color Accumulation)")]
[RequireComponent(typeof(Camera))]

public class MotionBlur : ImageEffectBase
{
	public float blurAmount = 0.8f;
	public bool extraBlur = false;
	
	private RenderTexture accumTexture;
	
	override protected void Start()
	{
		if(!SystemInfo.supportsRenderTextures)
		{
			enabled = false;
			return;
		}
		base.Start();
	}
	
	override protected void OnDisable()
	{
		base.OnDisable();
		DestroyImmediate(accumTexture);
	}

	// Called by camera to apply image effect
	void OnRenderImage (RenderTexture source, RenderTexture destination)
	{
		// Create the accumulation texture
		if (accumTexture == null || accumTexture.width != source.width || accumTexture.height != source.height)
		{
			DestroyImmediate(accumTexture);
			accumTexture = new RenderTexture(source.width, source.height, 0);
			accumTexture.hideFlags = HideFlags.HideAndDontSave;
			Graphics.Blit( source, accumTexture );
		}
		
		// If Extra Blur is selected, downscale the texture to 4x4 smaller resolution.
		if (extraBlur)
		{
			RenderTexture blurbuffer = RenderTexture.GetTemporary(source.width/4, source.height/4, 0);
			accumTexture.MarkRestoreExpected();
			Graphics.Blit(accumTexture, blurbuffer);
			Graphics.Blit(blurbuffer,accumTexture);
			RenderTexture.ReleaseTemporary(blurbuffer);
		}
		
		// Clamp the motion blur variable, so it can never leave permanent trails in the image
		blurAmount = Mathf.Clamp( blurAmount, 0.0f, 0.92f );
		
		// Setup the texture and floating point values in the shader
		material.SetTexture("_MainTex", accumTexture);
		material.SetFloat("_AccumOrig", 1.0F-blurAmount);
		
		// We are accumulating motion over frames without clear/discard
		// by design, so silence any performance warnings from Unity
		accumTexture.MarkRestoreExpected();

		// Render the image using the motion blur shader
		Graphics.Blit (source, accumTexture, material);
		Graphics.Blit (accumTexture, destination);
	}
}