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 caustics disabled, objects which do not cast shadows, lights with "emit light" 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:

    -Reflection environment override may not work correctly on materials with reflection glossiness lower than 1 (directly visible environment will be 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 lack of reflections on the teapot:

    -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).

  • LightMix (3ds Max | C4D) may produce unexpected results when using it with lights having "fake" (non-physical) properties enabled, such as "occlude other lights" option disabled:

  • LightMix (3ds Max | C4D) does not interactively update shadow catcher material shading results.
    Solution: use the ">Scene" button in LightMix to bake light properties into scene objects.

    Beauty render element:

    LightMix result:

  • 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

  • Multitexture in BerconTile mode is not supported.

  • Using Bidir/VCM render engine with IR 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.

  • 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: 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.

3rd party software issues

  • 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 - 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.