Thorsten Froehlich wrote:
> It is a necessity because "look_at" is just a simplified way to modify those
> vectors.

Yes, but why ? To my non-programmer's ears, it does not sound more 
complicated to rotate the vectors instead of defining new ones. But I 
suppose that even a tad more complicated would imply a noticeable 
slowdown if the function is called for each ray. Right ?


> And it is well documented in 3.5 as well...

As I wrote earlier, I was posting from memory without access to pov nor 
the doc. Now I checked some, but I did not find any reference of look_at 
redefining perpendicular up and right. However, I found some references 
that could be corrected because they talk about a rotation of the 
camera, which is not what is happening - although I agree it is the 
easiest explanation, as few user would specify non-normal 
direction/right/up on purpose.

---
3.1.3
Also look_at <0,1,2> rotates the camera to point at the coordinates 
<0,1,2>.


6.4.1.1
The look_at vector tells POV-Ray to pan and tilt the camera until it is 
looking at the specified x, y, z coordinates.


6.4.1.2
Normally POV-Ray pans left or right by rotating about the y-axis until 
it lines up with the look_at point and then tilts straight up or down 
until the point is met exactly.
[...] Then it uses the sky vector as the axis of rotation left or right 
and then to tilt up or down in line with the sky until pointing at the 
look_at point.
[...]
The sky vector does nothing on its own. It only modifies the way the 
look_at vector turns the camera. The default value is sky<0,1,0>.


6.4.1.5
The primary purpose of the up and right vectors is to tell POV-Ray the 
relative height and width of the view screen.
[...]
In the default perspective camera, these two vectors also define the 
initial plane of the view screen before moving it with the look_at or 
rotate vectors.

----

BTW, is anybody up to patching pov for using vista buffers with 
non-perpendicular direction/right/up ? I guess it should not be too 
hard, but what do I know ?


Povingly,

Philippe

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