"sumdumguy" <nomail@nomail> wrote in message 
news:web.4927c762fb7773f43b34ecfe0@news.povray.org...
>I have a scene where only a small part gets changed frame to frame so I 
>want to
> render the first frame fully and then the following frames only for a 
> selection
> of rows and columns, automatically keeping the rest of the pixel values
> unchanged from first frame. How do I do this?

I don't think there's a straightforward way of doing this. If your desire to 
do this is to save render time you may well find you expend more time 
developing a technique to glue all the bits together than you save when 
rendering. However, if you're driven by some other motive then there are a 
variety of approaches that spring to mind (all of which involve some 
external post-processing).

You don't say whether each of the subsequent frames would be an identical 
selection of rows and columns. If you want different rows and columns in 
each frame then you'd need to invoke POV-Ray from the command-line (e.g from 
a script) with different command-line options for each frame. Otherwise you 
could use one POV-Ray render for the first frame and an animation sequence 
(e.g. +kfi1 +kff100) to generate all the other frames.

There are partial animation command-line options, which may be of value to 
you (see +sc in the help). If the rows and columns you want to render from 
frame 2 are centred on the middle of frame 1, then you may find it easier to 
adjust the width and height (+w +h) and compensate using the up and right 
camera vectors (or the angle attribute), because then you don't have the 
post-processing effort required to isolate the rendered sections from the 
rest of the images.

Assembling the images into a single animation is always done outside of 
POV-Ray using whichever tool serves you best. The technique you develop 
would need to correspond with the capabilities of the utility you plan to 
use and the format you wish to generate. For example, the GIF constructor 
set (to build animated GIFs) allows you to retain a previous image and 
overlay a new partial image at a particular location, so this would probably 
lend itself to the technique of adjusting the width and height with the up 
and right vectors.

Regards,
Chris B.

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