Reference Talk:Camera

Aspect Ratio

Together the right (width) and up (height) vectors define the aspect ratio of the resulting image.

A Change in version 3.8 redefines how the right vector default is derived. Previously a fixed value it is now a calculated value that is based on the image width and height specified at render time. As usual, the image width and height can be specified from either the pull down menu available in GUI versions ONLY or the +Wn and +Hn command-line options available to ALL versions. This behavior is conditional upon the last effective #version directive before the camera definition. The use of the angle keyword is generally discouraged, as it defines the horizontal viewing angle and will affect the aspect ratio and appearance of the resulting image.

To retain legacy behavior see the example below:

#version X.y; // X.y is a version less than 3.8
camera {
  location <3,5,-10>
  look_at <0,2,1>
  }