Scratch Card Is not smooth using SetPixel()

Questions & Answers
1

Hi,

I want to implement a scratcher where user can scratch the foil to reveal the content on card. For the following I used unity SetPixel(). But it’s not smooth when user reveal vigorously.

My code is as follow :

public class Scratcher : MonoBehaviour
{
		public UITexture mTex;

		private Texture2D texture;
		private float erasedPixels;

		private int textureWidth = 28;
		private int textureHieght = 28;

		void  Start ()
		{
				// Create a new texture and assign it to the renderer's material
				texture = new Texture2D (textureWidth, textureHieght, TextureFormat.RGB24, true);

				GetComponent<UITexture> ().material.SetTexture ("_SliceGuide", texture);

				// Fill the texture with white (you could also paint it black, then draw with white)
				for (int y = 0; y < texture.height; ++y) {
						for (int x = 0; x < texture.width; ++x) {
								texture.SetPixel (x, y, Color.white);
						}
				}
				texture.Apply ();
		}

		void Update ()
		{
				if (Input.GetMouseButton (0) && UICamera.hoveredObject != null && UICamera.hoveredObject.tag == "ScratchFoil") {

						Vector3 localPos = transform.InverseTransformPoint (UICamera.lastHit.point);
						Vector2 uv;

						uv.x = localPos.x / (float)mTex.width;
						uv.y = localPos.y / (float)mTex.height;

						Texture2D tex = texture;

						Vector2 pixelUV = uv;

						pixelUV.x *= tex.width;
						pixelUV.y *= tex.height;

						// add black spot, which is then transparent in the shader
						tex.SetPixel ((int)pixelUV.x, (int)pixelUV.y, Color.black);
						tex.Apply ();
				}
		}
}

Now I applied this script on my NGUI UITexture which contains a material with a shader used to clip the current texture RGB value from _MainTex.

Shader As follow :

 Shader "mShaders/ScratchEffect" {
    Properties {
      _MainTex ("Base (RGB), Alpha (A)", 2D) = "black" {}
      _SliceGuide ("Slice Guide (RGB)", 2D) = "white" {}
      _SliceAmount ("Slice Amount", Range(0.0, 1.0)) = 0.9
    }

    SubShader {
      Tags {"Queue" = "Transparent" "IgnoreProjector"="True" "RenderType" = "Transparent" }
      Cull Off

      CGPROGRAM
      #pragma surface surf Lambert alpha
      struct Input {
          float2 uv_MainTex;
          float2 uv_SliceGuide;
          float _SliceAmount;
      };

      sampler2D _MainTex;
      sampler2D _SliceGuide;
      float _SliceAmount;

      void surf (Input IN, inout SurfaceOutput o) {
          clip(tex2D (_SliceGuide, IN.uv_SliceGuide).rgb - _SliceAmount);
          o.Albedo = tex2D (_MainTex, IN.uv_MainTex).rgb;
          o.Emission = tex2D (_MainTex, IN.uv_MainTex).rgb;
          o.Alpha = tex2D (_MainTex, IN.uv_MainTex).a;
      }
      ENDCG

    }
    Fallback "Diffuse"

  }

Everything working fine to it just this SetPixel() is sucking a lot of frame per second and not giving smooth scratch effect.

Anybody help me out with this trouble.

Thanks in Advance.

2

You should avoid using SetPixel() so often. It is much more efficient to use SetPixels().

Perhaps in Update() you could maintain a list of pixels you need to set. Then, after a certain threshold, apply the pixels you were recording via SetPixels() as a batch. You could play with the threshold such that it is not very noticeable.