Known bugs and limitations


This article lists bugs and limitations in Corona Renderer which we are aware of, and which we are planning to fix in the future. If you have encountered any of the issues listed below, there is no need to report it to us.


For bugs and limitations related to volumetric FX (Phoenix FD, FumeFX, CoronaVolumeGrid, CoronaVolumeMtl), see this separate article.




Known Bugs / Problems


  • Light transport issues
    These issues are some of the most commonly encountered by the users, yet they are extremely hard to fix for our development team. Corona Renderer is intended for realistic, physically-based rendering, and the following issues usually appear if non-physical ("fake") properties are used for objects and materials. Such properties include, but are not limited to: 
    • Refractive materials with disabled caustics
    • Objects which do not cast shadows
    • Lights with "emit light" option disabled



Sometimes "black highlights" or other artifacts may appear on objects with reflection glossiness level lower than 1. Example cases:

"Black highlights":
- Black reflection of sunlight may be visible on materials with glossiness lower than 1, if sunlight is passing through a Corona Light material with "emit light" option disabled:

Correct result - the plane uses a Corona Light material with "emit light" option enabled:

Incorrect result - the plane uses a Corona Light material with "emit light" option disabled:


- Lights may produce incorrect results (for example will be visible in reflections as dark spots) if they are behind objects with "cast shadows" object property disabled:

Correct result - the blue plane casts shadows:
 
Incorrect result - the blue plane has "cast shadows" property disabled:


- Reflections of lights may appear dark under specific conditions (e.g. if they have "visible in reflections" option disabled):

Correct result - the light is visible directly, in reflections, and in refractions.

Incorrect result - the light has visibility in reflections disabled:


Other:
- Reflection environment override may not work correctly on materials with reflection glossiness lower than 1 (directly visible environment will be incorrectly reflected):

Correct result - HDRI is used as scene environment:

Incorrect result - HDRI is used as scene environment, however black reflections override has been enabled, so the expected result would be complete lack of reflections on the teapot:


- Using reflection/refraction environment overrides with HDR images may result in persistent fireflies:
Solution: use low dynamic range images as environment overrides (e.g. convert from .HDRI to .JPG).


- Reflections in solid glass may look different when caustics are disabled and enabled when reflection glossiness lower than 1 (e.g. 0,99):

Reflection glossiness 0,99, caustics disabled:

Reflection glossiness 0,99, caustics enabled:

Solution: use a rayswitch material. Plug the glass material with caustics disabled into the Global illumination slot of the rayswitch material, and plug the glass material with caustics enabled into all other slots:


- Reflection of solid glass appears "bent" or "skewed" even if seen on a flat surface.

- Appearance of refractive materials changes when reflection glossiness other than 1 is used (even if it's set to 0,999). The workaround here is to enable caustics for the refractive material.



  • Transparent materials seen through global volume material (volumetric fog) may look incorrect.
    Solution: increase Enviro distance value in Development/Experimental Stuff rollout (3ds Max | C4D).




  • Material Library 
    Undo history (moving, scaling, rotating, changing properties, etc) is cleared after dragging and dropping a material from the library onto any scene object in the viewport. Using the undo icon or pressing Ctrl+Z will only undo the most recent action, which is assigning the material to the object.
    This is a 3ds Max issue, and it appears in the native material editor as well. An example report about it from 2008 can be found on the Autodesk forums




Interactive rendering limitations


  • Resetting the scene or closing 3ds Max during rendering (regular or interactive) may sometimes cause a crash. This is a 3ds Max limitation, and we do our best to prevent it, however we cannot guarantee 100% stability.



  • Multitexture in BerconTile mode is not supported.



  • Using the experimental Bidir/VCM render engines with interactive rendering may result in black screen or even crashes.



  • Selection marquee and region selection frame may be invisible when using IR.



  • 3ds Max atmospheric effects - using them while IR is running may lead to instability (lags, freezing, incorrect output).



  • Velocity render element cannot be previewed in the interactive rendering VFB.





Known limitations and unfinished features


  • Bidir/VCM- experimental render engines (3ds Max | C4D)

    Many advanced or fake features are not supported (image filters, blend material, enviro overrides, invisible to camera, …):

    Progressive render engine:




    The same scene, with the same materials render using Bidir/VCM render engine:




  • [3ds Max] Falloff map in Shadow/Light mode is not supported:





  • [3ds Max] "Lock sampling pattern" option does not work when using Corona's distributed rendering.



  • [3ds Max] Multi/Sub-Object material is currently not supported when nested inside Blend, Double-sided, and Top/Bottom materials



  • [3ds Max] Particle Motion Blur Map (Particle MBlur) is not supported. It may render incorrectly or cause crashes.
    Solution: use Corona's native motion blur with particles - it should not introduce significant speed penalty.



  • Geometry Motion Blur does not work for geometry with changing topology (changing number of faces, vertices, or normals).



  • Motion Blur does not work on objects scattered with Corona Scatter.


  • Corona AO (Ambient Occlusion) map cannot be used in Corona Scatter (for example as a distribution mask). This is because Corona AO can only work during the rendering, and using it as a mask for Corona Scatter would require it to work before the rendering is started. 


  • There are differences between how geometry is created with different 3ds Max versions. Currently we are aware of Teapot and Circle objects (differences between 3ds Max 2019 and 2020) and Sphere object (differences between 3ds Max 2016 and 2017). This may result in Corona Scatter rendering differently in different versions of 3ds Max if instances are scattered on those offending objects (and possibly some other object types which we have not identified yet).

    Some cases where this can happen include:
    • Opening a scene created with an older version of 3ds Max in a newer version of 3ds Max and re-rendering (the scattering may be different, for example the instances may be aligned in a different pattern).
    • Rendering a scene using distributed / network rendering where some render nodes are running an older version of 3ds Max and some nodes are running a newer version of 3ds Max (in this case different computers may render different scattering, which can result in scattered objects appearing and disappearing in animations, or showing half-transparent). 
      Note: it is generally not recommended to mix different versions of 3ds Max when using distributed / network rendering!


Possible workaround: open your scene in the version of 3ds Max it was originally created in, convert the offending objects to editable poly, save your scene, and only then re-render it with the newer version of 3ds Max.
Note: unfortunately this is a 3ds Max-related issue, so we might never be able to guarantee identical rendering between different versions of 3ds Max.


  • Instancing is disabled when applying CoronaLightMtl to instances with "emit light" enabled. This may lead to long scene pre-processing and excessive memory usage.
    Solution: use self illumination if possible. (3ds Max | C4D)



  • Light emitters cannot be ray-switched (example impossible setup: light material which is directly visible as black, but emits blue light).
    See:"Light material in Ray-Switch" forum thread



  • 3ds Max Projection modifier is not yet supported for the Render To Texture feature.



  • Limitations of the new caustics solver (Corona Renderer 4 and newer) - see: How to render with the new caustics solver? 








  • In 3ds Max 2016, when changing the frequency of an instanced object in a Corona Scatter, it causes the list to scroll immediately to the top, and the selected object no longer appears to be selected. This is a 3ds Max issue, and it also happens in other parts of the UI, even when Corona Renderer is not installed.



  • Corona MultiMap cannot be used with the 3ds Max native BlendedBoxMap (only one map will be projected onto all axes).
    Solution: use the Corona TriplanarMap instead of the 3ds Max BlendedBoxMap.



  • Corona EXR (.CXR) is not supported by some 3rd party software and service providers. It may not work properly with region/tile/strip rendering.



  • 3ds Max native photometric lights do not scale well with multi-processor systems and therefore may introduce significant performance drop.
    Solution: remove the photometric lights, or replace them with Corona lights.



  • It is not recommended to use objects, modifiers, or materials which are native to other renderers than Corona, unless they are officially listed as compatible - this can lead to hard to diagnose problems, even if initially everything appears to work correctly.



  • Itoo ColorEdge is no longer supported by developers and frequently causes 3ds Max crashes.



  • Message “Error Creating File Output”: caused by 3dsmax bug that adds non-existing paths to render elements.
    Solution: go through your render elements and delete all non-existing output paths, or fix render element paths in the asset tracker (Shift+T).