Voxel Mask

A voxel mask marks part of the model so you can cut along it: take the marked region away, keep only that region, or split the model in two. Open the Modify accordion in the Voxel sidebar and click Mask. Its tools open in the Numeric window (the window opens if it was closed); click Mask again to put them away. Mask, Cut and Add share the Numeric window, so only one of them is open at a time.

Mask tools

The top row of the Numeric window holds the mask tools. Click one to arm it, then work in any view; click the lit icon again to disarm it. Every tool masks normally and unmasks while you hold Ctrl.

Tool	What it does
Mask Paint	Paint the mask onto the model with a brush.
Mask Lasso	Draw round the area to mask.
Mask Box	Drag a rectangle to mask.
Mask Circle	Drag out from the centre to mask a circle.
Mask Poly	Click the corners of a polygon; close it on the first corner or with Enter.
Fill	The last icon is a button, not a tool: it masks everything at once.

While Mask Paint is armed, two sliders appear under the icons: Size, the brush in screen pixels (2 to 400, 40 to begin with), and Strength (0.05 to 1.00, full strength to begin with). A lower strength builds the mask up over several strokes.

Front Face or Volume

The two buttons under the icons decide how deep Lasso, Box, Circle and Poly reach. Front Face, the starting choice, masks only the surface the view can see. Volume masks straight through the model at every depth, hidden surfaces and the inside included — use it when the cut should go right through, for example to take the whole end off an arm from a side view.

Editing the mask

Control	What it does
Show mask	Shows or hides the mask's tint on the model.
Clear	Removes the whole mask.
Invert	Swaps masked and unmasked.
Grow	Spreads the mask outward.
Shrink	Pulls the mask in.
Blur	Softens the mask's edge.

Cutting with the mask

The three buttons at the bottom of the panel turn the mask into a cut. The masked region becomes a new node in the Voxel Tree, so the cut is part of the scene's recipe like any other shape: delete that node and the cut is gone. With nothing masked, they tell you to paint a mask first.

Button	What it does
Cut Away	Cuts the masked region out of the whole model. The cut appears at the top of the Voxel Tree as Mask cut.
Keep Only	Keeps only the masked region of the model. It appears at the top of the tree as Mask keep.
Split	Splits the model in two along the mask: a Masked group and an Unmasked one, ready to move apart.

Split is the one to use when you want both halves — a lid and its box, a head and its body. The Unmasked group holds the model with the region cut away and the Masked group holds a separate copy of the model with only the region kept, so each can be moved, turned and edited on its own.

Select (Face)

Select (Face), the wide button under Mask, Cut and Add in the Modify accordion, selects a flat surface for you. Click the model and the connected surface facing the same way is selected. The selection is the mask: it shows in the mask's tint, and the Mask panel's buttons use it.

Clicking the button arms the pick and opens its settings in the Numeric window. Click the model to select a surface; hold Shift to add to the selection, or Ctrl to remove from it.

Control	What it does
Pick a surface	Arms or disarms the pick. While armed it reads Picking: click a surface.
Angle tolerance	How far a point's surface may turn from the one you clicked and still be selected, from 0 to 90 degrees. The starting 5 degrees takes a flat face; more takes a gently curved one.
Follow curves	Compares each point with its neighbour instead of the point you clicked, so a surface that curves gradually is selected however far it turns. Off to begin with.
Show selection	Shows or hides the selection's tint (the same switch as Show mask).
Clear, Invert, Grow	The same as in the Mask panel.