Mirrors And Portals
Question submitted by (13 July 1999)

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  I recently have coded a portal engine with mirrors and all that stuff everytime i find a portal i Adjust the clipping planes to it clipping this fustrum with the previous fustrum of course. The portals have to be defined clockwise in order to create the correct fustrum the problem is that when i see trough a mirror the poligons are now anti clockwise (I use clockwise poligons) and i dont know how to solve this... i think that there sould be a good hack around but i dot get it :)

so given a portal is there a good way to generate the clipping planes for it without taking care of the clock/anticlock-wise of the portal?

  a quick hack: to set a flag to indicate which direction along the vertex array(s) you wish to traverse. if the resultant frustum is constructed from a "mirror" portal, set the flag to -1, +1 otherwise.

Response provided by Hin Jang

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