[Visualpython-users] Pitfall with 'forward' and 'up'

[Thomas P. <tp...@gm...>]

Hi,
I'm still working with version 3.2.1, but judging from the
changelogs, the pitfall should still be present in the
current release.

I tried to setup a scene such that the z axis is pointing
upwards and the camera is looking along the y axis:
#####################################################
from visual import *

# 1 / does not work
scene = display(up=(0, 0, 1), forward=(0, 1, 0))

# 2 / does not work
scene = display(forward=(0, 1, 0), up=(0, 0, 1))

# 3 / works
scene = display(forward=(1, 0, 0), up=(0, 0, 1))
scene.forward = (0, 1, 0)

arrow(pos=(0,0,0), axis=(0,1,0))
#####################################################

The canonical solutions 1 and 2 both do not work, because
the new up direction is colinear with the default forward
direction (1) or the new forward direction is colinear with
the default up direction (2).

Solution 3 works, but it's not really easy to come up with
this solution for a beginner.

A simple fix would be to wait with the colinearity check until
all keywords have been processed.

Cheers,
Tom

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