Unity shader pixel manipulation - unity3d

Question

I'm studying shaders in unity and I'm trying to achieve the below image. But I can't seem to make my code produce my target output. My end goal is to divide the whole image depending on the size of my array. Any idea how to correct my code?
Target output:
Code:Shader "Custom/PassArray"
{
Properties
{
_MainTex ("Texture", 2D) = "white" {}
}
SubShader
{
Tags {"Queue"="Transparent"}
Blend SrcAlpha OneMinusSrcAlpha
Pass
{
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#include "UnityCG.cginc"
uniform float4 _Test [3];
struct appdata
{
float4 vertex : POSITION;
float2 uv : TEXCOORD0;
};
struct v2f
{
float2 uv : TEXCOORD0;
float4 vertex : SV_POSITION;
};
v2f vert (appdata v)
{
v2f o;
o.vertex = mul(UNITY_MATRIX_MVP, v.vertex);
o.uv = v.uv;
return o;
}
sampler2D _MainTex;
fixed4 frag (v2f i) : SV_Target
{
fixed4 col;
_Test[0] = fixed4(0,0,1,1);
_Test[1] = fixed4(1,0,0,1);
_Test[2] = fixed4(0,1,0,1);
//Test1: This code block produces output1 image.
int index = round(i.uv.x*_Test.Length);
col = _Test[index];
//Test2: This codeblocks outputs pure green.
//if(i.uv.x < 1/3){
// col = _Test[0];
//}
//else if(i.uv.x < 2/3){
// col = _Test[1];
//}
//else if(i.uv.x < 3/3){
// col = _Test[2];
//}
return col;
}
ENDCG
}
}
}
Actual output:
If I understood it correctly, it's giving me black pixels because of the max i.uv.x is 1. Thus making the index 3 (based on the computation i.uv.x/_Test.Length). But I don't have index 3 in my array though.

Answer 1

Change round to floor. Because you're rounding, values greater than 2.5 get rounded to 3. As you probably know, an array of 3 elements has no index 3, hence the black bar.

Answer 2

I've figured it out. Here's the updated code for anyone who may find it useful. I changed the formula from int index = round(i.uv.x_Test.Length); to int index = ceil(i.uv.x/1_Test.Length)-1;
Shader "Custom/PassArray"
{
Properties
{
_MainTex ("Texture", 2D) = "white" {}
}
SubShader
{
Tags {"Queue"="Transparent"}
Blend SrcAlpha OneMinusSrcAlpha
Pass
{
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#include "UnityCG.cginc"
uniform float4 _Test [3];
struct appdata
{
float4 vertex : POSITION;
float2 uv : TEXCOORD0;
float4 color : COLOR;
};
struct v2f
{
float2 uv : TEXCOORD0;
float4 vertex : SV_POSITION;
float4 color : COLOR;
};
v2f vert (appdata v)
{
v2f o;
o.vertex = mul(UNITY_MATRIX_MVP, v.vertex);
o.uv = v.uv;
return o;
}
sampler2D _MainTex;
fixed4 frag (v2f i) : SV_Target
{
fixed4 col;
_Test[0] = fixed4(0,0,1,1);
_Test[1] = fixed4(1,0,0,1);
_Test[2] = fixed4(0,1,0,1);
//Test1:
int index = ceil(i.uv.x/1*_Test.Length)-1;
col = _Test[index];
return col;
}
ENDCG
}
}
}