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Scene Troubleshooting

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This article covers information on how to troubleshoot a scene and determine the cause of its issue. 

 

Overview

You may come across various types of issues when working with or rendering a scene. Such could be artifacts, slow rendering, large memory consumption, crashing, stalling, incorrect geometry and/or lighting, etc.

Such issues are usually caused by something within the scene, for instance: 

  • Render settings

  • Material/Map

  • Geometry

  • Light

  • 3rd party plugin

  • Imported assets (from a library or other software)

  • Rarely,  Hardware malfunctioning

  • etc.

In order to find a solution, it’s necessary to isolate the culprit and deal with it properly.

Since a scene usually contains thousands of objects, this process may not be as easy as it sounds. It’s important to streamline the troubleshooting method to quickly narrow down the problematic area of the scene. Reducing the suspects accelerates the debugging procedure significantly.

 

Adjust Settings for Quick Rendering

Scene debugging requires a lot of re-renderings. To speed up this process it’s important to tweak the scene to render as quickly as possible. The following options could be used to speed up the rendering.

  • Tweak Render Settings for faster rendering:

    • Use small image resolution or a region render;

    • Use Bucket Sampler with Min/Max subdivs of 1;

    • Disable global features like GI, Displacement, Subdivision and etc.;

    • Remove unneeded Objects, Materials, Maps

Note: the changes mentioned above might prevent the issue from reproducing.
In such cases follow the bullet points individually and track which one resolves the
problem to investigate further.

 


Check Render Settings (Resetting V-Ray Render Settings)

Resetting the V-Ray settings to their defaults is a simple step to determine whether the issue lies in the setting values or status.

Oftentimes parameters are wrongly interpreted or exaggerated. It is recommended to start the debugging process by restoring to the Default Render Settings. This is a quick and effective step to save troubleshooting time. If the issue persists, continue the investigation elsewhere. 

 

Comparе Current Render Settings with the Defaults

Should reverting to the default render settings resolve the issue, you might not understand which particular parameter/s caused the problem. To find out, the previous and current render settings should be compared. This can be done in several ways.

 

Compare Render Settings in the V-Ray Frame Buffer (3Ds Max)

By using the Compare V-Ray Settings feature in the V-Ray Frame Buffer (VFB) you can compare the current render settings to the render settings of an image stored in the History. It can be used to quickly compare the Scene Render Settings to the Default ones. To do that:

  1. Render the scene with the original settings.
  2. Save the output in the VFB History.
  3. Reset the Render Settings ().
  4. Right-click on the image in the History window and select Compare V-Ray Settings.
  5. A new window pops up and displays the Settings with the altered values.

compare_vray_settings_3dsmax.gif

 

Compare Render Settings Using the Technical Documentation

The Default Render Settings are displayed as screenshots on their relevant page in the Chaos Documentation. Use the values as a comparison reference.

 

Compare Render Settings Using a .vrscene File

You can manually compare the render settings of several scenes via export to a .vrscene file.

To check the differences in the render settings, compare the troublesome scene with a default (empty) scene. Text editors like Notepad++ (Compare plugin) or Online text editors could be used for this purpose. Here is a step-by-step guide:

  1. Export the original scene to .vrscene file: 3ds Max / SketchUp / Rhino / Maya/ Revit / Unreal / Cinema 4D / Modo / Nuke / Houdini / Blender.
  2. Export a new empty scene to a .vrscene file.
  3. Open both files into a text editor and start the Comparing mode.
  4. Look for sections starting with Settings, for example:
      • SettingsOutput vraySettingsOutput {
      • SettingsOptions vraySettingsOptions { 
      • SettingsImageSampler vraySettingsImageSampler {

compare_vray_settings_notepad.gif

 

5. By comparing both .vrscenes you could quickly find the differences between the parameters. These are the potential suspects.

6. To find out if a specific parameter causes the issue, restore it to its default value and render the scene.

 

Check Materials/Maps (Override the materials)

Another method for narrowing down the cause of an issue is overriding the scene materials with a default V-Ray material. If the issue is resolved by doing so, it means it lies in the scene shading.

Overriding all scene materials can be done by:

Note: for scenes where illumination comes through transparent materials, it is advisable to exclude
those shaders. You can quickly do that by selecting the transparent materials and adding them
to a new layer. Exclude this newly created layer from the material override settings.

If the issue disappears when all materials are replaced with the default V-Ray Material, the narrowing down continues to the specific material/s or map/s causing it. This could be achieved in the same way, but rather than replacing materials globally, you replace them individually. To speed up the process use the following approaches:

  • Replace non-V-Ray Materials/Map - the issue may be caused by an unsupported Material/Map of another render engine.

  • Replace Materials/Maps of imported objects/libraries - imported assets from 3rd party libraries/software are sometimes questionable.

  • (3ds Max) Run the V-Ray Scene Converter. Make sure all material checkboxes are enabled. 

  • (Maya) Run the Convert Scene for V-Ray tool.

  • Replace multiple materials at once. A good strategy is to replace half of the materials and check for the issue. If it’s still there, continue replacing materials until it disappears, When the issue disappears, undo the last replacement and focus on those materials.

Once the problematic Material/Map is found it could be replaced with similar material or it could be recreated from scratch. The troubleshooting process could dive deeper by going through the parameters of the problematic Material but in most cases, this is not needed.

 

Check Geometry

If the issue is not found in the render settings or materials, it could be caused by the geometry. The possible origin could be:

  • Imported geometry from a third party software/library (not self-made geometry);

  • Overlapping faces/edges/vertices;

  • Inverted/manipulated normals;

  • Options in the Object Properties and V-Ray Properties sections;

  • Other

To find the corrupt geometry start deleting parts of the scene until the issue stops reproducing.

if you have lots of geometry in the scene delete the objects that are not in the view first. Afterward, begin removing the visible ones half by half, rendering after each removal, until you find the culprit.


Check Lights

You can quickly test whether the lights are causing issues by disabling all of them in the Light lister and creating a dome light or a directional light instead. This should give you good overall lighting of the scene, which serves as a good basis for comparison and/or drawing conclusions. 

If the issue is with specific light, you have to track it down and start testing with it. Refraction, reflection, specular render elements can tell with which part of the output image the lights have problems with.

 

Convert Scene (3dsMax)

V-Ray for 3ds Max has a very handy feature called V-Ray Scene Converter for converting non-V-Ray objects like materials/cameras to V-Ray ones. It’s recommended to run it with all checkboxes enabled and see if it resolves the issue or not.

 

Fast Pre-check

  • Third-party plugins - Issues may occur due to incompatibility or lack of support for a third-party plugin. Disable all other add-ons to determine if the issue is related to them;

  • Render with VRayStandalone (this way you find if the issue is V-Ray related);

  • Camera - you can remake the camera if you think it is the culprit;

  • Volume rendering, effects, simulations, displacement - remove/ disable those for faster preview if they are not the case for the search;

  • Render the scene with an older V-Ray Version if you are sure it worked differently before. Check the new and the unsupported features.

  • Check the render elements - they are great tools for tracking down issues as they help you specify their source. For example, you can check whether it is in the reflections, lighting, GI, SSS materials, etc.

  • Reproduce the issue on a simple scene instead - sometimes a scene is hefty and cumbersome to debug and takes too much time. This is the case where you can try the basic functionality of an idea on a simple scene to make sure that it generally works this way.

  • Lookup for the same issue on Chaos Group Forums. A lot of the issues have been already discussed and the solutions can be found there.

  • If you are experiencing a crash, check the Memory consumption and V-Ray log files for errors. 

  • Memory stats / Rays Stats;

  • What has been changed since the last working state of the scene?

 

Conclusion

If you can't determine what is going on with your scene, please reach us using the Support Form and send it along with a report of all of the above-mentioned findings.

If the issue is scene-specific, it would be best to send us the scene and the accompanying assets. Please note that stripped-down scenes work best due to the low file size and faster testing times.

 
 
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