Instancing geometry and mattes

[Russle]

Hello Odforce!

 

I have found mantra to behave quite weird when it comes to instancing and mattes. I have a simple example scene where I want to render the instanced geometry with a matte. When rendering with the physically based engine it starts rendering after 2 or 3 seconds. When rendering with the micropolygon engine, mantra needs more than 15 seconds before it starts rendering. Now this can become troublesome if for example you have 5000 medium stones you want to scatter across a landscape and want another 10000 small stones. 

I am asking this because I have the my actual scene where rendering time won't start until 45 seconds with the micropolygon engine. The problem is that I have to use micropolygon because I'm rendering volumes and want to matte out geometry.

I have included a demo file to show you the problem.

Thank you in advance for your suggestions!

 

Shadow_Matte.hip

Edited September 19, 2016 by Russle

[davpe]

whart is the problem then? 45 sec startup time? how long does your render take? have you tried simply raytrace it?

[TheDude]

"I have to use micropolygon because I'm rendering volumes and want to matte out geometry." Raytracing / pbr works fine for this

JG_Shadow_Matte.hip

[Russle]

On 22-9-2016 at 8:16 PM, davpe said:

whart is the problem then? 45 sec startup time? how long does your render take? have you tried simply raytrace it?

The problem is that 45 seconds on 432 frames is 5.4 hours of extra startup time. Not to mention that I have 2 volumes that need separated rendering, plus the shadows that need to be rendered. Doing this seperated is faster then in one PBR render. Plus this gives nice control in comp too.

On 23-9-2016 at 10:10 PM, TheDude said:

"I have to use micropolygon because I'm rendering volumes and want to matte out geometry." Raytracing / pbr works fine for this

JG_Shadow_Matte.hip

Thank you for your example file, I have not tried ray tracing because recommendations are that you use micropolygon when rendering volumes (in my case an explosion and fire). I found that here (scroll all the way down).

Quote

Rendering Pyro effects

• You may want to decrease the division size (that is, increase the resolution) of your containers before rendering.

• Render Pyro effects using the micropolygon engine (Mantra render node > Properties tab > Render tab >Rendering Engine).

I have also tried upping the number of stones in the scene. When you add for example 10000 stones the time to fire up micropolygon is 120 seconds plus. In my case I have 30840 instance points to render. That would take more time to start the micropoly engine then it would to render the frame.

Edited September 27, 2016 by Russle

[davpe]

yeah... well choosing render engine for volumes is not that straightforward as documentation suggests. I find myself using micropoly only for very large volumes for which raytracing it is not reasonable for time/sampling reasons. Working with micropolygon is less straightforward and generally more hassle than raytracing. Many times, using raytrace (with raytraced lights) gives better looking results and better motion blur with similar or faster render time. Using PBR can make your render much slower without noticeable visual difference, but may be an advantage if you want to sample indirect volume rays.

So which render engine to use very much depends on the individual situation. Try experimenting with all render engines and with render settings and you will see what gives you the best results. You are able to matte out the geometry with any engine. It is not something that only micropoly can do.

In any way, if your renders are so fast that 45 sec before actual rendering makes a noticeable difference then I presume you are storing much more volume data than your renderer is actually sampling (either due to render settings or huge empty bounding box that needs to be clamped). If the bounding box seems to be fine then you may want to downsample the volume first to something that is adequate to your render settings (so it won't take 45 sec to load).