Corona Decal is a very convenient way of projecting textures and materials onto surfaces:
A manhole, cracks, and road signs projected onto a road using the Corona Decal object.
Note: Decals are now added to the Chaos Cosmos.
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 a surface where the normals are flipped (180 degrees compared to the decal object) is not possible any more.
"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:
Additional examples
A Corona Decal with no bump map, projected onto the asphalt material which does have a bump map:
The "Replace base bump" option in the stop sign decal makes the decal appear flat, as there is no bump used in the decal material.
Disabling the "Replace base bump" option in the decal will make the decal inherit the bump effect from the underlying asphalt material:
The stop sign decal can have its own bump map. When the "Replace base bump" option is disabled, the decal's bump will be added to the underlying material's bump:
Enabling the "Replace base bump" option again will leave only the decal's bump:
The same principle applies to Displacement:
By default, "Replace base displacement" is disabled, resulting in adding the underlying material's and the decal's displacements together. If the asphalt material has a displacement map and decals with displacement are projected on it, this is how it will look with "Replace base displacement" disabled:
Enabling "Replace base displacement" will result in the desired look in case of decals like manholes:
Overlaying many decals with varying vertical positions and options can quickly produce good-looking results:
Note: Corona Decal can be used in combination with other Corona features, for example: