"sumdumguy" <nomail@nomail> wrote:
> 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?

Depending on what changes and what else is in the scene, you could render the
static background, then render the animated part without anything else around
and use the alpha channel to composite.  You may also be able to achieve this
even if there is some degree of scene interaction (such as reflections or cast
shadows) by using the no_image, no_shadow, and no_reflection modifiers.

Of course, if a 'background' object occludes the animated object at some point,
it would need to be re-rendered with it and composited also.  Furthermore,
using radiosity in your scene will depend on the locations of all objects
present, which means that trying this technique with radiosity will not look
like it should.  There is also the issue of shadows cast by your object...

Some of the above issues can be worked around by clipping the entire scene into
a small box that moves with the moving object and having the background alpha'd
for compositing.  If you lengthen this box along the axis of the camera, toward
the camera, this could also ease occlusion problems.  It may take some work to
get such a thing going, you may still save some time.


-Reactor

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