How does FRUSTUM camera work?

[EriTheSwitch]

Godot Version

v4.4.1.stable.arch_linux

Question

While both PERSPECTIVE and ORTHOGONAL camera modes are pretty clear in how they work, I’m struggling to understand how do you set up a FRUSTUM camera - unfortunately, documentation does not do a good job describing how it works either.

First of all, it’s quite apparently more or less just a perspective camera with an extra feature (frustum offset) and a different way to set it up. Cool. However, I’m confused about how it’s set up: it’s evidently controlled by the near and size properties, but what exactly they specify eludes me.

First of all, unlike other camera modes, here changing the near property actually affects what the camera sees (and the result is quite something for low values). Second, size property would seem to set the size of the camera’s near plane (aka what’s seen on the screen, much like in orthogonal camera), but looking at the camera gizmo seems to imply that it changes as you change the near property. Or is the gizmo basically lying and the near plane is located right at the camera origin in this mode?

Any help with understanding this camera mode works would be greatly appreciated!

[yesko]

The near and far planes determine at what distances objects are “cut off” from the view. So, for example, with near = 1 and far = 4000, objects closer than 1 and further than 4000 aren’t visible anymore. The camera’s sides seem to be “anchored” on the near plane, so depending on its size and position they will be angled differently. As far as I know, size determines the size of the near plane (as you said) which changes the angle between the sides of the camera, aka its size. Since near controls the distance from the near plane to the origin without changing the size of the plane, this also affects the angle/size of the camera’s frustum.

That’s how I understand it, sorry if there are any mistakes.