CODEWITHSUNDEEP
opengl3dwebglprojection
Real Donald Trump
Real Donald Trump

Reputation: 422

When perspective division is necessary?

I'm very confused when it is necessary for a homogeneous coordinate (x, y, z, w) get divided by w (ie. converting to (x/w, y/w, z/w, 1)).

According to this page, when a homogeneous vertex coordinate is passed through a orthographical or projective matrix, the coordinate will be in clip coordinates. Perspective division is necessary for clip coordinates to get NDC. It will produce x, y, and z values in range (-1, 1).

I was following WebGL tutorial pages on orthographical and perspective projection. These tutorials didn't mention a single word about perspective division. I'm not sure if the division is still necessary after multiplying with projective matrix. Perhaps, the division is performed automatically during matrix multiplication?

Upvotes: 2

Views: 706

Answers (1)

Nicol Bolas
Nicol Bolas

Reputation: 474236

The perspective divide (the conversion from clip space to NDC space) is neither necessary nor unnecessary; it is a part of the graphics pipeline. It happens automatically to every vertex that passes through the system.

You can make it into a no-op by setting a vertex's W component to 1.0 (which is what the orthographic projection matrix does, assuming the input position had a W of 1.0). But the division always happens.

Upvotes: 3

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