Shader black and white threshold post-processing effect in Unity

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Preface

In the previous article, we explained Unity post-processing scripts and Shaders. In this article we implement a black and white post-processing Shader

• Post-processing scripts and Shaders in Unity

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1. Let’s first look at the effect of black and white threshold in PS

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2. Use the step(a,b) function to achieve the effect

由PS内效果可得出，使用step函数可以达到类型的效果
在PS内，黑白阀值是值越小越白，而step函数 a<b 才返回1（白色）
所以，我们让 控制变量 为 a ,颜色通道 为 b。实现出一样的效果

fixed4 frag (v2f_img i) : SV_Target
{
	fixed4 col = tex2D(_MainTex, i.uv);

	return step(0.2,col.r);
}

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3. Implement script control of black and white thresholds

1. Define the control threshold variable in the Shader property panel

_Value(“Value”,float) = 0.2

2. Change a in step to _Value

fixed4 frag (v2f_img i) : SV_Target
{
	fixed4 col = tex2D(_MainTex, i.uv);
	return step(_Value,col.r);
}

3. Set public member variables in the post-processing script, and set the range to (0, 1)

[Range(0,1)]public float Value = 0;

4. Before assigning the material to Graphics.Blit, assign a value to the _Value of the material.

private void OnRenderImage(RenderTexture source, RenderTexture destination)
{
	Mat.SetFloat("_Value",Value);
	Graphics.Blit(source,destination,Mat);
}

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4. Final code and effects

Shader:

Shader "Hidden/P2_7_4"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _Value("Value",float) = 0
    }
    SubShader
    {
        // No culling or depth
        Cull Off 
        ZWrite Off 
        ZTest Always

        Pass
        {
            CGPROGRAM
            #pragma vertex vert_img
            #pragma fragment frag

            #include "UnityCG.cginc"
            
            sampler2D _MainTex;

            fixed _Value;
            
            fixed4 frag (v2f_img i) : SV_Target
            {
                fixed4 col = tex2D(_MainTex, i.uv);

                return step(_Value,col.r);
            }
            ENDCG
        }
    }
}

C#:

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

//后处理脚本
[ExecuteInEditMode]
public class P2_7_3 : MonoBehaviour
{
    [Range(0,1)]public float Value = 0;
    
    public Shader PostProcessingShader;
    
    private Material mat;

    public Material Mat
    {
        get
        {
            if (PostProcessingShader == null)
            {
                Debug.LogError("没有赋予Shader");
                return null;
            }
            if (!PostProcessingShader.isSupported)
            {
                Debug.LogError("当前Shader不支持");
                return null;
            }
            //如果材质没有创建，则根据Shader创建材质，并给成员变量赋值存储
            if (mat == null)
            {
                Material _newMaterial = new Material(PostProcessingShader);
                _newMaterial.hideFlags = HideFlags.HideAndDontSave;
                mat = _newMaterial;
                return _newMaterial;
            }
            return mat;
        }
    }

    private void OnRenderImage(RenderTexture source, RenderTexture destination)
    {
        Mat.SetFloat("_Value",Value);
        Graphics.Blit(source,destination,Mat);
    }
}