How to use Interactive Rendering?



What is Interactive Rendering?


Interactive Rendering automatically updates the rendered image in real time as you make changes in your scene. It is a great aid in modifying and transforming objects, tweaking and creating materials, adjusting environment, lights, camera, and virtually any part of the rendered scene. All of this can be done while rendering, without any kind of limitations. There is no need to manually restart or update the rendering, as it happens automatically usually within less than a second. It runs completely on the CPU, so it has no limitations and does not require any special hardware.


Any kind of rendering done in Corona, including IR, is solely CPU-based. 



Are there any differences between regular and interactive rendering?


In Corona Renderer, final frame rendering and Interactive Rendering (IR) are handled by the same engine. In fact, final frame rendering is exactly the same as Interactive Rendering, only with scene updates disabled. The outputs of IR and final rendering are not visually different, as they are both capable of producing exactly the same effects, support the same features, and even use the same GI solvers. IR, just like regular VFB rendering, will react to exposure controls and other post-processing effects in real-time. The only differences are:


  1. When rendering, IR gives immediate response, while regular rendering is faster in the long run. This means that Interactive Rendering should not be used to produce finals. 
  2. IR internally uses slightly different render settings than regular rendering (for example lowered GI vs. AA balance). This is done to achieve best responsiveness, and does not affect the image quality or appearance in any way. 
  3. By default, IR does not use all CPU threads, so it is slightly slower in the long run than regular rendering. This is to allow for viewport navigation and other background activities to run smoother. This can be changed under system tab > system settings. 



How to use Interactive Rendering?


Note: Interactive Rendering in Corona Renderer cannot be enabled using the 3ds Max "Active Shade" option!



There are two Interactive Rendering modes in Corona:


1. Docked in viewport

To enable it, right-click on the name of a viewport of your choice (for example [top], [left] or [perspective]) and select Extended Viewports > Corona Interactive.




This will set your current viewport as an Interactive Rendering window. To start rendering, simply left-click anywhere inside that window. You can resize your interactive window's size by resizing the viewport layout. 


To stop the Interactive Rendering, click on the "Options" button in the top right corner of the IR view, and select "Stop":




To disable Interactive Rendering completely in the current viewport, either right-click inside it, or left-click inside it and press "V" key, and then pick any item from the drop-down menu:




Note: you can also left-click inside Interactive Rendering window and press "C" key to copy the content of Interactive Window into 3ds Max VFB - this is useful for example when you want to save the image generated in the Interactive View.



2. Undocked (floating window)

To enable it, go to Render Setup > Scene > General Settings and press the "Start interactive" button. This will open Corona VFB with Interactive Rendering running. To resize it, simply resize the VFB window - Interactive Rendering window is independent from output size specified in render setup, but its proportions are locked based on that. 




To stop rendering, simply close the VFB or use the built-in VFB controls:





Troubleshooting


1. Interactive rendering changes viewing angle each time I pick another viewport!
 

To lock interactive rendering to specific viewport, so that it does not change when you switch to another viewport, go to Render Setup and with the viewport of your choice selected, press the small lock button at the very bottom of the window. 

Note: this will not lock IR to your currently selected camera, so if you switch to another camera or perspective view within one viewport, IR will update anyway. This only locks IR to a single viewport. 




2. IR is rendering black screen only!

This could mean there is no light in your scene. Make sure you have added at least one light source.



3. Interactive rendering does not work!

Please see this guide for a possible solution: I cannot see Corona VFB!



4. How to optimize CPU usage when using interactive renderer?

Interactive rendering utilizes a lot of computing power which may sometimes result in increased heating and CPU fan noise. To reduce these, you can use "# of threads override" and "Max passes" options which are available in Render Setup > Performance > Performance Settings > Interactive rendering.
"# of threads override" 
is the number of cores to use for interactive renering. Positive values work in straightforward way. Value of 0 means that all system cores will be used. Negative values will use all cores but the number specified (-1 means all cores but 1).
"Max passes" 
limits the number of passes rendered in the interactive mode.