I have been so confusing about the w component for ages, until I read this:
Explaining Homogeneous Coordinates & Projective Geometry
So I quickly made a simple to shader to test it out:
To summarize, w component is the
The W dimension is the distance from the projector to the screen(object).
when w > 1, the object looks far (smaller)
when w = 1, the size remains the same
when w = 0, it’s actually covering the whole screen
This is the reason why we have make sure the w component is correct when we are doing _Object2World and _World2Object
Also a interesting point to note from the blog post:
If W=1, then it is a point light. If W=0, then it is a directional light.
(Thanks Kemal for the tutorial links!)