[Bf-committers] Proposition: Multilayer EXR support

[Ton Roosendaal]

Hi,

It's not upside down, it's an accepted & documented option in exr that  
has issues... both directions are allowed, but when i worked on it  
there were weird things in the windows version of openexr or so... too  
long ago to recall. Investige this?

-Ton-

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Ton Roosendaal  Blender Foundation   ton at blender.org    www.blender.org
Blender Institute   Entrepotdok 57A  1018AD Amsterdam   The Netherlands

On 29 Jan, 2010, at 15:34, Jeroen Bakker wrote:

>  * Problem statement
> Multilayer EXR files are used in 2 places.
>
> 1. to temporarily store the render buffers to reduce the memory
> footprint between the render pass and the composition pass.
> 2. to store the final output image as a multilayer exr.
>
> the problem is that multilayer exr's are stored upside down. For 1  
> it is
> not a problem as the file is temporarily and used by blender renderer.
> for 2: the output image makes the file's not easilly usable. You first
> have to flip the image, before you can use it.
>
> * Expectation
> the temporarily file must still be stored in the current form (upside
> down) for performance reasons.
> the output file must not be stored upside down, but still have all
> render layers available. (open file with exrdisplay -C
> RenderLayer.Combined.R filename.exr to see problem)
>
> Identifying the problem.
> both accesses the same function in openexr_api.cpp and both are
> triggered from the pipeline.c (blender renderer), but both have
> different requirements:
>
> * Proposition/alternatives
> there are several options how we can solve this:
> 1. leave all the same, but just before writing the multilayer exr  
> output
> image, flip all render buffers. The implementation of the multilayer
> does not use the imbuf API, so will not effects other file formats and
> is easilly doable
> 2. update the imbuf api, to support multilayer images. more work, but
> more futureproof to possible other (professional, non existing) output
> formats
> 3. use the exr tiles to save the image upside down (is something in
> between solution 1 and 2)
>
> I would have chosen for option 1 as it is not that much work, and I
> don't know what the requirements are for other professional output
> formats. Solution 3
>
> Other issues in this area: the multilayer has is no default image/ 
> layer;
> all images are default black in other applications like nuke or  
> exrdisplay.
>
> What do you think what is the wise thing to do?
> @Brecht, Campbell, is it OKE to patch pipeline as you are  
> restructuring
> the renderer?
>
> Greetings,
> Jeroen Bakker.
>
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