Help with understanding basic surface shader - UV to Albedo

Unity Engine
,
1

Hello,

I am new to shader coding and I am trying to make sense of some of the basics. In particular I am trying to better understand uv coordinates by visualising them.

I am using a basic surface shader and I am assigning the i.uv.x and i.uv.y floats to o.Albedo in order to see what they look like.

I would expect the result to be exactly the same as in my understanding both i.uv.x and i.uv.y range from 0 to 1 and should be float numbers.

However, when I assign them to o.Albedo I get different results. See pictures.

7613974--946093--UV X.jpg
7613974--946093--UV X.jpg2299×1376 281 KB
7613974--946090--UV Y.jpg
7613974--946090--UV Y.jpg2299×1386 285 KB

Here is the code, extremely simple and standard:

Shader "Custom/MyFloorShader"
{
    Properties
    {
        _Color ("Color", Color) = (1,1,1,1)
        _MainTex ("Albedo (RGB)", 2D) = "white" {}
        _Glossiness ("Smoothness", Range(0,1)) = 0.5
        _Metallic ("Metallic", Range(0,1)) = 0.0
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 200

        CGPROGRAM
        // Physically based Standard lighting model, and enable shadows on all light types
        #pragma surface surf Standard fullforwardshadows

        // Use shader model 3.0 target, to get nicer looking lighting
        #pragma target 3.0

        sampler2D _MainTex;

        struct Input
        {
            float2 uv_MainTex;
        };

        half _Glossiness;
        half _Metallic;
        fixed4 _Color;

        // Add instancing support for this shader. You need to check 'Enable Instancing' on materials that use the shader.
        // See https://docs.unity3d.com/Manual/GPUInstancing.html for more information about instancing.
        // #pragma instancing_options assumeuniformscaling
        UNITY_INSTANCING_BUFFER_START(Props)
            // put more per-instance properties here
        UNITY_INSTANCING_BUFFER_END(Props)

        void surf (Input IN, inout SurfaceOutputStandard o)
        {
            float2 uv = IN.uv_MainTex;
            /*Albedo comes from a texture tinted by color */
            fixed4 c = tex2D (_MainTex, IN.uv_MainTex) * _Color;
            o.Albedo = uv.x; //uv.y;
            //Metallic and smoothness come from slider variables
            o.Metallic = _Metallic;
            o.Smoothness = _Glossiness;
            o.Alpha = c.a;
        }
        ENDCG
    }
    FallBack "Diffuse"
}

Can anybody help me understand?

2

UVs are a position within a texture where (0.0, 0.0) is the bottom left corner and (1.0, 1.0) is the top right. The uv.x is horizontal position, and uv.y is the vertical position, which when you visualize individually will show a gradient going from black to white across those directions.