Re: [Openexr-devel] Appending to a partially rendered image

[Piotr Stanczyk]

Hey -

There is not an open mechanism to do that sort of thing right now. 
If you are willing to look at the source code then the Preview Image attribute is handled in just such a way. I presume that having something like this refactored into an open API would be useful?

- Piotr

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From: openexr-devel-bounces+address@hidden [openexr-devel-bounces+address@hidden on behalf of Richard Hadsell address@hidden
Sent: 17 June 2013 15:33
To: David Aguilar
Cc: address@hidden
Subject: Re: [Openexr-devel] Appending to a partially rendered image

On 06/17/2013 06:10 PM, David Aguilar wrote:

Not necessarily, but my answer is not strictly an "append" operation.

Here's one way that might work.  EXR files have a notion of a
"dataWindow" which is separate from the display window; they can be
different.

I'm imagining that you could set the data window to be just the region
that does exist; later you can "append" to the image by reading in the
current data (as defined by the data window) and filling in the
missing regions; eventually the data window will be equal to the
display window size, and the image will be complete.

This implies that you (or one of the apps you use, e.g. Nuke) is not
already using the dataWindow header for something else.  The absolute
safest thing is to invent your own custom header, e.g.
"completedScanlines" or whatever you want to call it, and manage the
custom EXR header yourself.

Can one modify the header of an output file after opening the file and writing some of the data?  I would want to modify the "completedScanLines" attribute after every scanline, before my app has to close or gets killed.  I also want to update some other attributes in the header, such as how long it took to render the image so far.

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