Usage:

• Use the command /portalgun to give yourself a portal gun
• Left click with the portal gun to shoot a blue portal
• Right click with the portal gun to shoot an orange portal

Rotation and momentum change direction relative to the angle you enter a portal. If you walk into a blue portal while facing it, you will walk out the orange portal while facing away.

Note: momentum is kind of conserved unless you enter a portal too quickly, after which you will come out of the other portal with no velocity. However, you can bounce up and down between two floor portals if you fall from the right height.