Masks and clipping
A layer with Mask on hides everything its children draw outside its own shape, plus Clipping Alpha, which keeps a layer's shadows and glows off the empty space around it.
Masking in Celas Studio works one way: a parent masks its own children. Nothing is clipped to the layer below it, and nothing is clipped to a sibling. If you want art confined to a silhouette, make the silhouette the parent, put the art inside it, and switch on Mask.
The mask is non-destructive. The shape keeps its own fill and stroke, the children keep their full artwork, and you can reshape the mask at any time.
Making a mask
- Nest the layers you want clipped inside the layer that will do the clipping.
- Right-click the parent in the Layers panel and choose Mask. The same toggle is the M dot on the parent's row in the Timeline.
- Everything the children draw outside the parent's shape disappears.
When several layers are selected, toggling Mask from the right-click menu applies to the whole selection.
What a mask needs to work
The Mask toggle is only offered on Shape, Raster and Pixel layers. A Shape mask has three further requirements, and all of them have to hold at once:
- The path has to be closed.
- It needs at least three points.
- The layer has to have at least one child.
A Shape mask is filled with the even-odd rule, so a hole punched by an inner contour is a hole in the mask too.
Raster and pixel masks
A Raster or Pixel layer used as a mask uses the alpha of its own painted cell rather than a path, which is how you get a soft-edged or brushed mask. Paint the mask layer, and the children show through wherever it has paint and fade where the paint is semi-transparent.
The parent's own paint is not multiplied against itself in this case, so semi-transparent brushwork stays at the opacity you painted it rather than getting twice as thin.
The parent stroke is never clipped
A masked Shape keeps its whole stroke, inside and out. The stroke is split at the mask boundary: the inner half is clipped along with the children, and the outer half is drawn underneath them. The result is one continuous stroke, and it means an Erase child inside the mask reveals the backdrop rather than eating into the parent's outline.
Where the stroke sits against the children is up to the Z-Order row in the Stroke section: Front draws it over the masked children, Inherit is the normal order, and Back puts it under the fill.
Clipping Alpha
Clipping Alpha is a different tool for a related problem. It is a switch in the Properties panel's Layer section, off by default, offered on everything except Bone and Camera layers.
With it on, the layer's outward effects (Drop Shadow, Outer Glow, and Outline when its Position is Outside) only land where the layers below it inside the same parent already have alpha. A shadow cast by an eyebrow stays on the face and stops at the edge of the head, instead of spilling onto the background.
The setting cascades: switch it on for a group and every layer inside it behaves the same way. Turning it on also puts the layer into its own isolation buffer, which is what lets the effect be masked against what is underneath.
Choosing between them
| You want | Use |
|---|---|
| Art confined to a shape | Mask on the parent |
| A soft or painted edge to the confinement | Mask on a Raster or Pixel parent |
| A shadow or glow that stops at the art below it | Clipping Alpha on the layer casting it |
| Part of a layer knocked out by another | The Erase blend mode inside a group: see Blend modes |