Gosh.

I wanted this feature for years and never realised (till now) that is was
there from the beginning. The problem : to achieve what some real-world
cameras can do : displace the film from its
central-and-parrallel-to-the-lens typical position. Solution : using non
perpendicular camera vectors. Thanks to MR for his "vanishing point??"
question in p.newuser that made me think (at last).

So, what are the practical implications ?

A typical problem : a scene with an "horizontal camera", that is camera
location.y and look_at.y are identical. The horizon is in the middle of the
image. If you want it somewhere else, you have to change the camera - which
you might not want to -, or render a bigger image and crop it in a drawing
software (partial render helps). OR use non orthogonal camera vectors ;-)

Another use : render a tall building as seen from sidewalk height without
having a vertical vanishing point.

Camera code for the example :
----
// Do not forget to switch vista buffers off (-uv) or it won't work.

#include "transforms.inc"

camera{

  #declare Cam_location=<0,.25,-1.5>;
  #declare Cam_Horizontal_look_at=<0,.25,0>;
  #declare Cam_Real_look_at=<0,1.125,0>;

  location 0
  direction .4*z

  #switch (clock)

  #case(0)  // horizontal cam
    look_at Cam_Horizontal_look_at-Cam_location
  #break

  #case(1)  // usual rotated cam, vertical vanishing point
    look_at Cam_Real_look_at-Cam_location
  #break

  #case(2) // sheared cam
    look_at Cam_Horizontal_look_at-Cam_location
    Shear_Trans(x, y, z+Cam_Real_look_at-Cam_Horizontal_look_at)
  #break
  #end

  translate Cam_location
}
---


Povingly,

Philippe

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