the input value for geometryshader

I'm trying to write a shader to get the wireframe without diagonal of model . I use lineadj as the value for input and hope to get four point to check it is a diagonal or not. However the point p[3](the fourth point) is always zero and when i draw it in my screen ,it stays at the center of my screen. Is the point data is right or I get some wrong code in my shader [maxvertexcount(12)] void geom(lineadj v2g p[4], inout LineStream<g2f> lineStream) { // float4x4 vp = UnityObjectToClipPos(unity_WorldToObject); float4 pos0 = mul(unity_ObjectToWorld, p[0].pos); float4 pos1 = mul(unity_ObjectToWorld, p[1].pos); float4 pos2 = mul(unity_ObjectToWorld ,p[2].pos); float4 pos3 = mul(unity_ObjectToWorld ,p[3].pos); g2f pIn0; pIn0.pos =mul(UNITY_MATRIX_VP, pos0); pIn0.col = float4(0,0,0,1); g2f pIn1; pIn1.pos = mul(UNITY_MATRIX_VP, pos1); pIn1.col = float4(1,0,0,1); g2f pIn2; pIn2.pos = mul(UNITY_MATRIX_VP, pos2)}; pIn2.col = float4(0,1,0,1); g2f pIn3; pIn3.pos = mul(UNITY_MATRIX_VP, pos3); pIn3.col = float4(0,0,1,1); lineStream.Append(pIn0); lineStream.Append(pIn2); lineStream.RestartStrip(); lineStream.Append(pIn1); lineStream.Append(pIn2); lineStream.RestartStrip(); lineStream.Append(pIn0); lineStream.Append(pIn3); lineStream.RestartStrip(); }