Not getting uniform thickness in wireframe shader - unity3d

Question

Shader "Custom/Geometry/Wireframe"
{
Properties
{
_MainTex ("Texture", 2D) = "white" {}
_WireframeVal ("Wireframe width", Range(0.000, 0.035)) = 0.05
_Color ("color", color) = (1, 1, 1, 1)
_BackColor ("Back color", color) = (1, 1, 1, 1)
}
SubShader
{
Tags { "RenderType"="Opaque" "Glowable" = "True" }
Pass
{
Cull Back
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#pragma geometry geom
#include "UnityCG.cginc"
struct v2g {
float4 pos : SV_POSITION;
};
struct g2f {
float4 pos : SV_POSITION;
float3 center : TEXCOORD0;
};
v2g vert(appdata_base v) {
v2g o;
o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
return o;
}
[maxvertexcount(3)]
void geom(triangle v2g IN[3], inout TriangleStream<g2f> triStream) {
float2 p0 = IN[0].pos.xy / IN[0].pos.w;
float2 p1 = IN[1].pos.xy / IN[1].pos.w;
float2 p2 = IN[2].pos.xy / IN[2].pos.w;
float2 edge0 = p1 - p0;
float2 edge1 = p2 - p1;
float2 edge2 = p0 - p2;
float area = abs(edge1.x * edge2.y - edge1.y * edge2.x);
g2f o;
o.pos = IN[0].pos;
o.center = float3(area/length(edge1) , 0, 0);
triStream.Append(o);
o.pos = IN[1].pos;
o.center = float3(0, 0, area/length(edge2) );
triStream.Append(o);
o.pos = IN[2].pos;
o.center = float3(0, area/length(edge0), 0);
triStream.Append(o);
}
float _WireframeVal;
fixed4 _BackColor;
float4 _Color;
fixed4 frag(g2f i) : SV_Target
{
if(min(i.center.x ,(min(i.center.y,i.center.z))) > _WireframeVal)
{
discard;
}
return _BackColor;
}
ENDCG
}
}
}
Here is my wireframe shader code
i am not getting uniform edges throughout
Also when i reduce the width almost to zero (0.0001) the some pixels of wires are not drawn what can i do for that ? I want to make the wireframe shader as unity's built it wireframe mode how can i achieve that ?

Answer 1

Actually, that is uniform thickness. You're just thinking about what "thickness" is in this context, due to how the object is being drawn.
On the edge of the cube facing the camera where it looks like it's thicker than the other edges. Well, you're half right. There is more white pixels drawn there.
But the reason for that is because there are two edges there! And each one is contributing the desired value towards the thickness of the wireframe.
Both the blue outlined face and the red outlined face are contributing to the thickness of that edge, whereas on a corner where the adjacent face is pointing away from the camera (say, the bottom edge of the blue outlined face), only one face contributes to the overall effect.
This isn't noticeable when the thickness is very small or very far away (because 0.2 pixels + 0.2 pixels = 0.4 pixels, round up: 1 pixel), but does become apparent at higher thickness values, or if you non-uniformly scale the object. For example, I have this in a project I was working on a few weeks ago (mind, mine draws the backfaces too and the alpha depth sorting is off):
The reason for this is because where the "edges" are is done through computing the barycentric coordinates of the triangle, which are just an approximation, and will give skewed results if the triangles aren't equilateral.