https://docs.unity3d.com/jp/current/ScriptReference/Texture2D.SetPixel.html

capture.png

checkTexture.shader

Shader "Unlit/checkTexture"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 100

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            
            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD0;
            };

            struct v2f
            {
                float2 uv : TEXCOORD0;
                float4 vertex : SV_POSITION;
            };

            sampler2D _MainTex;
            float4 _MainTex_ST;
            
            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = TRANSFORM_TEX(v.uv, _MainTex);
                return o;
            }
            
            half4 frag (v2f i) : SV_Target
            {
                // sample the texture
                half4 col = tex2D(_MainTex, i.uv);
                col = half4(1.0 < col.r, frac(col.g), col.b < -0.1, 1);

                return col;
            }
            ENDCG
        }
    }
}

TestCode.cs

using UnityEngine;

#if UNITY_EDITOR
using UnityEditor;
#endif

public class TestCode : MonoBehaviour
{
    public TextureFormat format = TextureFormat.RGBAFloat;
    public Texture2D tex;
    public Material mat;

    // Use this for initialization
    void Start()
    {
        tex = new Texture2D(512, 512, format, false);
        for (var y = 0; y < tex.height; y++)
            for (var x = 0; x < tex.width; x++)
                tex.SetPixel(x, y, new Color((float)x / tex.width, (float)y / tex.height, (float)(x + y) / tex.width, 1) * 2.0f - Color.gray);
        tex.Apply();
        mat.mainTexture = tex;
#if UNITY_EDITOR
        AssetDatabase.CreateAsset(tex, "Assets/tex.asset");
#endif
    }
}