Has anyone else discovered this with Iray trick to speed renders?
CGHipster
Posts: 241
Hi, I'm sure other people know about this, so if you do know then k, if you didn't read on. I have noticed that the first Iray render always takes the longest in any series of renders if I am rendering frames or many stills of the same set. But then I discovered something pretty interesting and it saves time in renders.
So, basically what I have been doing is once I put my first figure in I do a render just the bare figure, I drop uber shader on it and do a render. I don't close the render or save it, I leave it open and just minimized so it is out of the way.
All other renders after that just fly, but it only works if I don't close the first render. Iray doesn't waste time loading that whole initializing part and simply runs into rendering. It has worked like this for me since I first noticed it months ago.
I had loaded in a figure of M6 and of course, waited while Iray initialized and loaded everything to begin the render, and then just by chance I didn't save the render but had minimized it and then tried another render and was surprised at how fast it rendered, almost half the time as the first. I tried this several times and could repeat the same speed results, and then I basically deleted the first render as a test and also all other renders and tried it and was met again with the loading iray part and it basically took 2x wait to do a full render.
So, if you know about it already you were probably holding out on the rest of us 
or if it is already in the commons it is long buried 
. But, IF you didn't know about it I hope you give it a try and see for yourself and save time on renders in the same scenarios I have mentioned.
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Comments
This trick has actually been discussed a number of times since Iray came out, but it's always worth repeating! Keeping the window open keeps the scene database in memory, so it doesn't have to be rebuilt each time. It works as long as you don't add new geometry or textures, which then requires the scene database to be regenerated or updated. The scene database does not (generally) need to be regenerated with anything related to shaders, which includes light settings, or camera angles or settings.
Thanks, so I'm not crazy after all!
Oh, one other trick which involves a 3rd party app that dramatically improves render times is Razer Cortana's Game Booster. It is geared towards hi GPU, hi Memory and CPU usage while eliminating bloat on the system. Using Cortana to optimize my system and shut down unnecessary system services or background apps has boosted my renders about 25%.
It is free to use, just have to provide an email to setup and for those who don't like that there are disposable emails you can use online to register, just google disposable email addy.
Oh, one question then regarding the iray database being loaded. So, theoretically, if I use the Iray in the viewport scenes would render faster since they are already in the iray database?
It's often more convenient to keep the Aux Viewport in Iray mode and keep it small.
You'll get the same pre-loading boost without impacting your main viewport performance.
To paraphrase Charles Dickens, "Rendering, more mecurial, will appear in his own good time."
Or to put it less literary, rendering is a ray tracing process and performance doesn't improve in subsequent renders. There are renderers that do that (store past ray traces, usually for faster animation) but I'm not aware Iray is one of them.
What makes it faster is that the rendering engine doesn't have to build the scene, compile shaders, create all the data structures that define objects, materials and light to hand to the rendering engine. The actual process of rendering the image (calculating the interactions between light and surfaces) doesn't change. What you reduce is the prep time that occurs before rendering actually starts.Awesome sauce
OK, I understand. Is that sort of like the Octane Render where it has the option for adaptive sampling?
If you timed the event, you'd probably find that setting your Preview to Iray and letting it do the initialization and then clicking Render will take up the same amount of time as setting the Preview to OpenGL and clicking the Render button, where it has to do the initialization at that point. While you do get a faster time between clicking Render and seeing something in the pop-up window, the total time elapsed doesn't change that much.
First I have heard of it. Thanks for sharing this tip.
Not notiecably so. Rendering time is more affected by the lighting and materials than it is the size of the image. There can be a little bit of difference, but if it's just your Aux viewport, I wouldn't worry about it. There are some settings that can improve your experience. The Daz Tutorial video on Getting Started in Iray discusses some options for Draw Style, etc. which can make things more responsive for you.