In the past, we uses
mul(UNITY_MATRIX_MVP, v.vertex) to convert vertex position from local to world space. v.vertex is float4 which has w component.
But in most cases w is = 1. To make vertex shader run faster, Unity replaced it with
UnityObjectToClipPos(float3 pos), which ignores w component even you pass a float4 position instead of float3.
For some advanced users who still need the w component in their custom shaders, here is a cheaper UnityObjectToClipPos() function which respects the w component!😄
// More efficient than computing M*VP matrix product
inline float4 UnityObjectToClipPosRespectW(in float4 pos)
return mul(UNITY_MATRIX_VP, mul(unity_ObjectToWorld, pos));