help~~why the line not straight?

[vsolutionvs]

why should i do for this kind of problem? Thank you.

[Dariusz Makowski (Dadal)]

What are your anti aliasing settings?

[svetlozar.draganov]

This is Antialiasing Issue - you have to increase its settings depending on which type of Image Sampler you are using.
Please view the following example: http://help.chaosgroup.com/vray/help...ampler.htm#ex1