Please cache bitmaps when starting the IPR

[Art48]

I noticed this in a scene with not many but very very large bitmaps:

When I open the scene and IPR-Render directly it starts up and loads the bitmaps as usual and it takes quite a while which is also normal given the first time they are used/cached.
Now the thing is when I render with the normal production renderer it only takes this long the FIRST time. After that when I re-render it uses the cached bitmaps.
Yet when you directly press the IPR Render button it will ALWAYS load the bitmap again and not cache it. Only when I use production it gets cached and is then also available for IPR and IPR starts up fast.

Steps to reproduce:
Open scene with a material which has a large bitmap applied (say 1.5GB uncompressed file size).
Render with IPR and notice the delay.
Cancel IPR and render again with IPR. Notice the same delay.
Re-Open the scene (close 3ds max)
Render with production renderer and notice the delay
Cancel render and press render again and notice the delay is gone since the bitmap has been cached.
Now you can also use IPR without a delay.

[^Lele^]

Convert your bitmaps to VRayHDRIs (RMC, no need to convert to tiled EXRs, just the loaders), and then set the texture cache size big enough (or to 0) in the render settings.
That will load them once per session, provided they'll fit in ram (nothing that can be done using max bitmap loaders, you see.).
EDIT: the "caching" you see is read caching, system-side, likely.

[Art48]

I am not sure if I understand you correctly. The HDRI loaders seem to be a good suggestion, but won't it also take some time with the exception that the HDRI loader loads them when rendering instead of prior?
And the caching I see being system-side how come it "works" (as in one time load, then cache) when using the production renderer, but not when using IPR?

[^Lele^]

I am not sure if I understand you correctly. The HDRI loaders seem to be a good suggestion, but won't it also take some time with the exception that the HDRI loader loads them when rendering instead of prior?

VRayHDRI Loaders will indeed load bitmaps at rendertime, as needed (ie. hit by a ray), and then proceed to cache them into the Texture Cache.
Said cache will not be updated unless there is a file change in any of the textures, and it's entirely governed in behaviour by V-Ray.

And the caching I see being system-side how come it "works" (as in one time load, then cache) when using the production renderer, but not when using IPR?

I am not privy to the code, but it could be the IPR can't do anything else with max bitmaps than force a reread, or it could just be a genuine limitation, something yet to be implemented, and so on: Vlado'd know.
I can confirm that with VRayHDRI loaders, the IPR caches just fine.