Corona Decal is a very convenient way of projecting textures and materials onto surfaces:
A manhole, cracks, and road signs projected onto asphalt using Corona Decal objects.
Corona Decal - Tutorial:
Note: Ready-made decals are also available the Chaos Cosmos!
In addition to the below content, see also: Corona Decal at the Chaos Documentation Portal
How to use it?
The easiest way to create a Corona Decal is by using the dedicated Corona Toolbar icon. It can also be accessed by typing "Decal" into the 3ds Max "X" menu or from the Command Panel > Create > Geometry > Corona > CDecal:
Corona Decal toolbar icon
"Create Corona Decal" in the 3ds Max "X" menu.
Corona Decal (CDecal) in the 3ds Max Command Panel.
A Corona Decal can be created in a similar fashion as the 3ds Max plane object:
- Click and drag will create a cuboid with some relative height, edge-to-edge creation method
- Ctrl + Click and drag will create a cube centered at the creation point
Note that the Corona Decal's pivot is always placed at the creation point and there is a default pivot offset of 0.3. This is to avoid decal texture and base surface overlapping, both for viewing and projection purposes.
Let's create a simple material and apply it to a Corona Decal object:
We can see that the texture on the Decal is stretched. "Fit to Bitmap...", just like in UVW Mapping, or "Fit to assigned mtl" options can be used to quickly get the correct proportions of the texture. In case there is already a material assigned, "Fit to assigned mtl" is the faster option:
The Decal's width and height will change automatically when the "Fit to..." options are used.
Let's start Interactive Rendering in the viewport:
The Decal currently has no opacity mask and that is why we see a white square around the smiley.
The mask can be set either in the Decal material's opacity channel or as a separate map in the Decal's Mask source options:
After adding a circular mask, the Decal now appears with a transparent background.
The Corona Decal will be projected onto surfaces which intersect with its bounding box. If we move the Decal object higher, the plane won't be intersecting with it any more, resulting in no projection at all:
"Max angle limit" defines the maximum angle at which the projection occurs. If the angle between the Corona Decal and the surface is lower than the specified "Max angle limit", the surface will receive the projection. This is how the Decal is projected with default settings:
Max angle limit set to 180 degrees (the default value).
"Max angle limit" of 180 degrees means the decal will be projected even on the backface (the sphere is hidden in the below image):
Corona Decal projection visible on the backface of the plane object.
Changing the "Max angle limit" to anything below 180 degrees will result in no projection on the backside of the plane:
Max angle limit changed to less than 180 degrees. Projecting the Decal onto the backside of a surface where is not possible anymore.
"Max angle limit" of 45 degrees will result in some clipping of the Decal on the sphere:
The Decal is projected on the the sphere object only up until the specified Max angle limit.
"Max angle blur" can be used to avoid sharp clippings around the max angle limit:
With the "Max angle blur" option enabled, there is a soft transition between the areas where the Decal is projected and where it isn't.
Corona Decals can form a stack. The projection order is based on the decals' vertical position - over or under another decal:
Bringing the red smiley lower:
Vertical placement of the Decals:
Note: Corona Decal can be used in combination with other Corona features, for example:
Affect base rollout
Starting with Corona 10, you can specify which base object(s) material channels a Corona Decal should affect:
Note: Both the decal and the base material need to be CoronaPhysicalMtl in order for decal channels to work properly!
If a channel is enabled, it replaces the corresponding base object material channel where the decal is projected. If a channel is disabled, e.g. Color - base object material color will be used instead.
"STOP" decal affecting all channels:
"STOP" decal affecting all but Color channel:
Note how the roughness, specular, and other channels are still being affected, only the Decal's color is gone now.
Bump and Displacement channels have an additional option - they can be added to the base layer.
If "Add to base" is disabled for Bump or Displacement, they will replace the corresponding base layer:
Bump channel enabled, "Add to base" disabled:
Decal material has no bump. Decal appears flat as it replaces the base bump.
Bump channel enabled, "Add to base" enabled:
Decal material still has no bump. Decal appears as overlaid on top.
If the decal has no bump in its material, the above result will be the same as disabling the Bump channel. This will leave the base bump unaffected:
The Decal can also have its own bump (dotted pattern) added on top of the base bump:
The same rules apply for the Displacement channel.
"Rest" is for all the other material channels, such as translucency, refraction, anisotropy, clearcoat, etc.
Note: Corona Decal can be used in combination with other Corona features, for example: