Texture coordinates inconsistent

Question

I tried tiling texture coordinates on a quad in unity for some debugging.

On desktop it had no problems but on android(old tablet) I see inconsistency in texture coordinates(Image links below show the results).
As we go from 0.0,0.0 to 1.0,1.0 the texture coordinates keeps becoming inconsistent. the inconsistency increases as the tiling values go up, Results in images are for 60,160.

my device's android version is 5.0 and GPU supports opengl es 2.0 not 3.0.

So I would like to know why is this happening on my tablet but not on my desktop ,would appreciate information about what is happening in the gpu that is causing it.

Shader I used-

Shader "Unlit/uvdisplay"
{
    Properties
    {
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }

        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;
            };

            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = v.uv;
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
                // sample the texture
                fixed4 col = fixed4(frac(i.uv*fixed2(60.0,160.0)),0.0,1.0);
                return col;
            }
            ENDCG
        }
    }
}

texcoord at origin
texcoord at the opposit end

Columbo Columbo · Accepted Answer · 2018-03-13T20:42:46

Not all Android devices support highp in the fragment shader, some older devices are limited to mediump.

In Unity terms, based on these definitions, it's as if you ask for float precision in your fragment shader, but you get half precision.

Not too much you can do about it except try to keep values near the origin to minimize error.

Also, on some of the devices that only support half precision, as long as you do nothing except sample the texture (i.e. don't modify or swizzle the texture coordinates before using it), the driver/GPU is able to use the full precision for the texture sampling.

Texture coordinates inconsistent

1 Answers