Stippled Shader?

I am trying to generate a stippled texture with a shader. My goal is that every second pixel is transparent. Unfortunatly my result looks like this:

My shader is applied on a fullscreen quad. I was wondering how I could achive stippling and furthermore define the boarder around a stippled pixel. Anyone has a hint?

 Shader "IndieEffects/Alpha-Blended Motion Blur Stippling" {
     Properties {
         _MainTex ("Texture(RGB)", 2D) = "black" {}
         _FrameAccumulation ("Accumulation", float) = 0.65
     }
     
     SubShader {
     
         ZTest Always Cull Off ZWrite Off
         Pass {
             Blend SrcAlpha OneMinusSrcAlpha
             //ColorMask RGB
             
                         CGPROGRAM
             #include "UnityCG.cginc"
             #pragma vertex vert
             #pragma fragment frag
             //#pragma fragmentoption ARB_precision_hint_fastest
             #pragma target 3.0
             
             struct v2f {
                 float4 pos : POSITION;
                 float2 uv : TEXCOORD0;
             };
 
             v2f vert (appdata_img v)
             {
                 v2f o;
                 o.pos = mul (UNITY_MATRIX_MVP, v.vertex);
                 o.uv = v.texcoord.xy;
                 
                 return o;
             }
             
             sampler2D _MainTex;
             float _FrameAccumulation;
             
             float4 col;
             
             half4 frag (v2f i) : COLOR
             {
                 col = tex2D(_MainTex, i.uv);
 
             
                 if((int(i.uv.x + i.uv.y)/i.uv.x == i.uv.y))
                     discard;
                 else
                     col.a = _FrameAccumulation;
                     
                 col.r = 1.0;
                 col.g = 1.0;
                 col.b = 1.0;
                     
 
                 return col;
             }
             
             
             ENDCG
             /*
             SetTexture [_MainTex] {
                 ConstantColor(1,1,1,[_FrameAccumulation])
                 Combine texture, constant
             }*/
         }
         Pass {
             Blend One Zero
             ColorMask A
             SetTexture [_MainTex] {
                 Combine texture
             }
         }
     }
     Fallback off
 }