Corona Decal is a very convenient way of projecting textures and materials onto your scene objects: graphics, surface imperfections, potholes, all within the 3D viewport and without UVW mapping.
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Ready-made decals are available the Chaos Cosmos browser!
Mask Source – Source of Decal alpha (blending) mask.
From Material – Assigned material's opacity channel will be used.
Map – Allows selected another, independent map to act as a mask.
Size:
Lock – Toggle constraint of aspect ratio between width and height.
Width – Decal width.
Height – Decal height.
Bend - Width [°]– Specifies bend angle of the decal in the width direction.
Bend - Height [°] – Specifies bend angle of the decal in the height direction.
Fit To Bitmap... – Fits the decal aspect ratio to match selected texture node or a texture inside selected material (use drag and drop) or a bitmap file (use drag and drop or click to select from HDD). The overall area of the decal is preserved.
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This does not set the decal material, only changes the dimensions.
Fit To Assigned Mtl – Fits the decal aspect ratio to match one of the textures of the currently assigned material.
Projection
Depth Limit – Limits the depth into which this decal is projected. Any surface beyond this distance will not receive the decal.
Max Angle Limit – Maximum angle deviation between the surface normal and the decal direction for which the decal will be used. This can limit the projection to only facing surfaces. A value of 90 degrees will remove projection from backfaces, while 180 degrees will project on all backfaces.
Max Angle Blur – Optional fuzziness (blending) on the edge of the max angel limit.w
Viewport:
Show Material Preview – Shows material preview on top of the decal in the 3ds Max viewport when a material is assigned.
Pivot Offset – Changing this value shifts the decal in its Z axis by changing the relative position of its projection start and its pivot. With value 0 the decal projection starts at the pivot and with value 1 it ends there.
UVW mapping
Real-world map size – Enables real-world size mapping for the textures used in the Corona Decal material.
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Affect Base
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Color – When enabled, the color of base material is replaced with decal material color on geometry where decal is projected. If disabled, the color of base material is unaffected.
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This only works when both the base material and the decal material are Corona Physical materials.
Specular – When enabled, the specular (IOR, metalness) layer of base material is replaced with decal material specular layer on geometry where the decal is projected. If disabled, the specular layer of base material is unaffected.
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This only works when both the base material and the decal material are Corona Physical materials.
Roughness – When enabled, the roughness of base material is replaced with decal material roughness on geometry where the decal is projected. If disabled the roughness of base material is unaffected.
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This only works when both the base material and the decal material are Corona Physical materials.
Opacity – When enabled, the opacity of base material is replaced with decal material opacity on geometry where the decal is projected. If disabled, the opacity of base material is unaffected.
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If source of decal alpha is set to be "From material", setting this property to enabled may lead to unexpected results.
Mask ID – When enabled, the decal will be visible in CMasking_ID render element (only if instance ID option is used).
Emission – When enabled, the emission of base material is replaced with decal material emission on geometry where the decal is projected. If disabled, the emission of base meterial is unaffected .
Bump – When enabled, the bump of base material is replaced with decal material bump on geometry where the decal is projected. If disabled, the bump of base material is unaffected.
Add To Base – When enabled, the decal material bump is added on top of the base material bump on geometry where the decal is projected. If disabled, the bump of base material is replaced with decal material bump.
Displacement – When enabled, the displacement of base material is replaced with decal material displacement on geometry where the decal is projected. If disabled, the displacement of base material is unaffected.
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The advanced displacement parameters (water level, vector displacement) are always taken only from the base object.
Add To Base – When enabled, the decal displacement is added on top of the base material displacement on geometry where the decal is projected. If disabled, the displacement of base material is replaced with decal material displacement.
Rest – When enabled, the rest of base material properties (those not specified in this rollout) are replaced with decal material properties on geometry where the decal is projected. If disabled, these properties of base material are unaffected.
Check All – Enables all checkboxes.
Check None – Disables all checkboxes.
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Creating a Corona Decal
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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:
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The Decal can also have its own bump (dotted pattern) added on top of the base bump:
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Example
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Bending
Bending gives you better control over projecting decals on cylindrical surfaces such as bottles or glasses, or even on spheres thanks to bending in two axes:
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Stacking Decals
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Overlaying many decals with varying vertical positions and options can quickly produce good-looking results:
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Affect Base
Only “Displacement” is enabled under the “Affect Base” section. This way, only the displacement map of the decal affects the base object's material. Otherwise, we would be also affecting other channels such as diffuse color or reflectivity.
By the way, the ripples on the water surface are also achieved with a decal using a procedural gradient map.
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Real-world map size
With the "Real-world map size" option enabled, the size of the textures used in the Corona Decal can be precisely controlled using real-world units such as centimeters or inches. In the below example, the size of the hole texture (opacity) is set to exactly 1.5m x 1.5m and the bricks have a realistic scale as well:
