proRender: initial render start super slow, then fast

The initial start of a ProRender View is super slow. For one specific model (32mb) it takes more than 2 minutes to actually even start the rendering process. Here is a timeline:

from shaded view ProRender is activated:

waiting for more than 2mins and as one can see the CPU/GPU are doing very little as far as I understand

then this view happens for another 10 seconds:

then finally it starts rendering, relatively fast (about 100passes per minute)

@Joshua_Kennedy, any ideas what could be the cause for this?

btw as a comparison, cycles is starting to render just after a few seconds and I don’t think that cycles is really fast yet on Mac…

Furthermore I should not, that this is happening with almost all of my larger models.

Thanks a lot,


I assume you’ve rendered before with ProRender? The first time a render occurs ProRender has to compile kernels for the GPU which is quite time consuming. This shouldn’t be causing an issue with every render though.

With large models there are a lot of meshes and materials that need to be sent to ProRender. This can be a time consuming process. ProRender also needs to set itself up internally before the rendering can begin. Two minutes is quite a wait though. It’s hard to know without seeing the model what exactly is going on. If you provide the model I can take a look.

thanks, I uploaded the exemplary file!

As an important side note/issue: proRender seems to crash a lot on my machine… happens very often, when I

a) stop a Rendering
b) switching form proRender raytraced display to shaded view (thus also stopping the rendering)

Would be cool, if you could also try rendering and stopping the rendering with the file I provided!


@Joshua_Kennedy, any updates, sir?


I’ve taken a look but couldn’t reproduce it. It’s still an open issue and I’ll continue to investigate further.

Don’t know what fixed it, but after installing the newest update the issue hasn’t happened again.
However: Rendering with 1920x1080, but once I render sth with a higher resolution, for example 3200x2400, the render image just turns black, as can be seen in the video:

Thanks for reporting. I’ll take a closer look soon but for now I’ve logged a bug.