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Pixelation Shader - Unity Shader


Pixelation Shader

This is the correct way (one of many) of showing pixelation as a post-processing effect.
This effect will work in any aspect ratio without any pixel size scaling issues as well as it is very minimal in terms of coding it up.
image effect that pixelates the screen
pixelate image effect in action

In order to get this to work 2 components have to be set up:
1) The pixelation image effect
2) The script - which will be attached to the camera

So let's get started by creating a new image effect shader.
We will take a look at our Shaderlab properties :
_MainTex("Texture", 2D) = "white" {}
That's it, Everything else will be private and not shown in the editor.
Now we will see what are defined along with the _MainTex but are private.
sampler2D _MainTex;
int _PixelDensity;
float2 _AspectRatioMultiplier;
We will pass _PixelDensity & _AspectRatioMultiplier values from the script.
As this is an image effect there is no need to play around with the vertex shader.
Let's take a look at our fragment shader:
fixed4 frag (v2f i) : SV_Target
{
   float2 pixelScaling = _PixelDensity * _AspectRatioMultiplier;
   i.uv = round(i.uv * pixelScaling)/ pixelScaling;
   return tex2D(_MainTex, i.uv);
}
That's it ? 😒
Well.... ya... But still, let me break it down.
Firstly let us take out the aspect ratio correction stuff :
i.uv = round(i.uv * 100.0)/ 100.0;
If you replace the previous i.uv statement with this one you will still see that the image is pixelated but if your game aspect ratio is anything other than a square then it will stretch horizontally if the game window width is more than it's height and vise-versa.
Now let's get into the meat of it :
The round function basically converts a float like 0.6 to 1 and 0.4 to 0; It converts a float with a decimal point to the closest integer.
The uv.x & uv.y values go from 0 to 1. So if you multiply uv co-ordinate (0.125, 0.125) by 100 then you will end up with (12.5, 12.5) and then round it, you will get (12, 12) then you bring it back into the 0 to 1 range by dividing by the same amount; Now it's (0.12, 0.12). These same result will be for uv co-ordinates (0.126, 0.126), (0.129, 0.129) etc...
So the output color will keep taking color input from the same uv co-ordinate. That's how the pixelation effect is achieved.
We will now see how the aspect ratio is corrected in the C# script.
using UnityEngine;

[ExecuteInEditMode, RequireComponent(typeof(Camera))]
public class PixelateImageEffect : MonoBehaviour
{
    public Material material;
    public int pixelDensity = 80;

    private void OnRenderImage(RenderTexture source, RenderTexture destination)
    {
        Vector2 aspectRatioData;
        if (Screen.height > Screen.width)
            aspectRatioData = new Vector2((float)Screen.width / Screen.height, 1);
        else
            aspectRatioData = new Vector2(1, (float)Screen.height / Screen.width);
        material.SetVector("_AspectRatioMultiplier", aspectRatioData);
        material.SetInt("_PixelDensity", pixelDensity);
        Graphics.Blit(source, destination, material);
    }
}
You might be familiar with the OnRenderImage function if you have been following the blog for a while.
This function runs after everything on screen is rendered and two render textures are passed into it, source & destination.
the source is the input RenderTexture and destination is the output RenderTexture. You perform some changes to the source and apply it on the destination. The Graphics.Blit(source, destination, material) is basically doing just that.

'material' property is the post-porcessing material that was made with the shader.
We pass in the values for the pixel-density and aspect-ratio multiplier with the material.SetInt() & material.SetVector() methods.
Now we determine the value of 'aspectRatioData' which is a Vector2.
The x component of aspectRatioData is the multiplier for x-axis of uv and y component is for y-axis of uv.
if (Screen.height > Screen.width)
    aspectRatioData = new Vector2((float)Screen.width / Screen.height, 1);
else
    aspectRatioData = new Vector2(1, (float)Screen.height / Screen.width);
So if the height was greater then the x component was the ratio between width and the height and the y component was 1 ( when multiplied will remain same ).
If the width is greater then the y component will be the ratio between height & width and x component will be 1.
I hope you learned something today. Do not forget to share this if you liked it.
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