Function viewBasis

The orthonormal camera basis lookAt builds, exposed on its own.

Extracted so the only other place that reconstructs a screen basis — CameraProjection.unprojectToRay's orthographic branch, which turns a cursor position into a picking/measurement ray — derives it from this function instead of recomputing cross(forward, up) itself (#2467). The duplicate was not merely a second copy: it had none of the degeneracy handling below, so a non-finite camera.up returned a ray whose origin was (NaN, NaN, NaN) while the rendered frame was perfectly fine. A NaN origin does not throw; it makes every t < tMin / dist < tolerance hit test false, so picking reports "clicked empty space" and a measurement silently refuses to snap.

That is also what settles what an unprojection should return when the basis is unusable, which is otherwise a matter of taste. It should return the ray for the basis the user is actually looking at: when up carries no usable orientation this function substitutes a deterministic hint and the view matrix — hence the rendered image — is built from that substitute. Deriving the ray from the same substitute makes picking agree with the picture. Returning null instead would fail a pick on a frame the user can see and interact with, and push a branch onto every caller of a published API.

eye is returned alongside the axes because it is scrubbed here too, and a ray origin must come from the same scrubbed eye the view matrix's translation row does.

All four vectors are always finite. right/up are unit length; forward points from eye towards target (the negation of lookAt's third row, which is the camera's backward axis).