This page provides a tutorial on using V-Ray's Resumable Rendering feature.
Resumable rendering is the ability to have incomplete renders resume where they left off from the previous session. The rendering could have stopped because of external forces, such as a power failure or having the job bumped on a render farm, or when you stopped the render manually and want to start from where you left off later.
How it works
With Bucket rendering, an additional .vrimg is written to temporarily store the data from the completed buckets. When you resume rendering, V-Ray will read the .vrimg file to determine which buckets still need to be rendered and continue to calculate what is left to complete the image.Another great ability of this feature is that the light cache is saved within the partial image file so it doesn't need to be recalculated when the render resumes.
When rendering with the Progressive image sampler, the state of the render is saved to an additional resumable .vrprog file in a similar way to the .vrimg for Bucket rendering. Enabling Autosave Interval (min) in the Frame buffer rollout (by setting it higher than 0) is highly recommended for Progressive renders so V-Ray can write out the .vrprog files during rendering in case the process is unintentionally stopped. Setting the Autosave Interval (min) value too low (below a couple of minutes for example) can slow down the render process.
If V-Ray finds a .vrprog file or partially completed .vrimg file for the current frame, the rendering will resume from where it left off. If not, V-Ray will start a new render and a resumable file is saved.
Example: Progressive Render
The images below were taken during a resumable Progressive render was stopped and restarted to complete the final image. This type of rendering can help when you need to get something reviewed, and then can continue to render for a cleaner end result.
Render Stopped after 2 passes
Render to the left Resumed, then stopped after 19 passes
Render in the middle Resumed, then stopped after 47 passes
Enable Save File from the Render Output section of the Common Parameters under the Common tab in the Render Setup window. Any of the three possible image outputs can be used (raw image file, separate render channels, Save File) for this step.
Note: Any of the acceptable file types can be used, except Bucket rendering does not support deep outputs or tiled EXRs at this time.
If you forget to set your file output, you will receive an error if you start a resumable render.
Error message if Render Output is not set
Before starting to render, enable Resumable rendering in the Frame buffer rollout under the V-Ray tab in the Render Setup window. If using the Progressive sampler, it is highly recommended to enable the Autosave Interval (min) by setting it higher than 0. This will save partial files that can be used and help prevent losing the render progress if Max crashes and a .vrprog file was not created/updated.
Start rendering your image. The passes will calculate for a Progressive render or the buckets will begin to drop for a Bucket render. The render can be stopped at any point in time and V-Ray will be able to use the .vrimg or .vrprog files to resume the render later.
If you stop the render and want to resume it on another computer or location, make sure to copy the .vrimg or .vrprog file with the rest of your project so V-Ray can pick up where the render left off. Render Settings should not be changed between stopping and resuming renders. The only settings that are acceptable to change in between stopping and resuming a render are Progressive sampling parameters (Min. subdivs, Max. subdivs, Render time, Noise threshold). Changing settings like the output resolution and render elements will cause an error and the render will not resume.
- Light Cache data is saved in the resumable files, but the Irradiance Map (or any other GI map) is not and will need to be recalculated when resuming. The rendering should still continue from where it was stopped after the GI data is recalculated.
- The Resumable Rendering option should be enabled before starting a new render, not only when resuming.
- To start a new render, the .vrimg/.vrprog file should be deleted.
- The scene should not be changed between stopping and resuming, except for the Progressive sampling options (Min. subdivs, Max. subdivs, Render time, Noise threshold).
- There are two output modes that are not currently supported for the Bucket Sampler - deep output, and tiled EXR output (without a memory frame buffer).
- On GPU, resumable rendering is only supported with Bucket sampler.