Selection & mask painting

Masks tell the simplifier where detail matters, what to protect and what may be removed. You can paint them directly on the mesh, or select triangles and UV islands first and turn the selection into a mask.

On this page

Selection
Highlight colours
Create Mask from Selection
Paint tab
Mask layer types

Selection

Menu item	Purpose
Enable Selection	Turns picking and highlighting on. Turn it off to hide the selection overlay (for example after you created a mask from it).
Triangle / Island	Pick single triangles, or whole UV islands (connected pieces of the texture layout).
Refine within selected islands	Limit triangle picking — and Select All / Clear / Invert — to the islands that are currently selected.
Lock Selection	Keep the current selection from changing.
Select All, Clear Selection, Invert Selection	As named.
Create Mask from Selection	Turn the selection into a new mask layer.

Selecting works in both the 3D viewports and the Atlas Editor. Hovering or clicking in one highlights the same triangles in the other, which makes it easy to reach geometry that is hidden on the model (inside the mouth, under clothing) but easy to find in the texture layout.

Island mode: click an island; Ctrl+click adds more islands.
Triangle mode: Shift+drag paints a selection over the surface.
Clicking empty space in the atlas clears the selection. Orbiting the camera may also clear it — frame your view first, then select.

Two islands selected, shown in the atlas and on the mesh — Two islands selected (green) in the Atlas Editor; the same islands light up on the mesh.

Triangle selection painted on the chest — Triangle mode: a patch painted with `Shift`+drag…

The same triangles in the atlas — …and the same triangles in the atlas.

Highlight colours

Colour (default)	Meaning
Magenta	Hover — a click would add this
Orange	Hover — a click would remove this
Teal	Hover on geometry hidden behind other geometry
Green	Selected
Dark green	Selected, but hidden behind other geometry

The colours can be changed in Settings > Selection highlight.

Create Mask from Selection

Selection > Create Mask from Selection adds a mask layer of type Remove made of the selected triangles. The confirmation shows how many triangles the mask would free at every LOD level, measured against the LODs you have now.

Paint tab

Brush

Control	Purpose
Navigate / Paint / Erase / Smooth	Navigate the camera without painting; add mask; remove mask; smooth the mask values.
Undo / Redo	`Ctrl`+`Z` / `Ctrl`+`Y`
Radius, Strength	Brush size and how strongly a stroke changes the mask. Small radii (around 1) are useful for precise corrections.
Falloff	Smooth, Linear or Constant towards the brush edge.
Mirror	Paint symmetrically.
X-ray	Paint through to geometry behind the visible surface.

Layers and the selected layer

The Layers list shows each layer's on/off state, name, type and weight. The buttons below it add, duplicate and remove layers.
Selected Layer: rename, change the Type and the Weight (0–100). The buttons Fill, Clear and Invert act on the whole layer.
Masks take effect when Apply mask layers is on in the Decimate tab and you generate (or refine) the LODs.

Layer list with a new Remove layer — A Remove layer created from a selection, next to three painted importance layers.

Mask layer types

Type	Effect on the LODs
Protect	Keep the painted area from being simplified.
Geometry importance	Spend relatively more triangles on the painted area (by its weight) — e.g. face and hands.
UV importance	Preserve the texture layout more carefully in the painted area — e.g. where texture detail matters, like hair.
Remove	Drop the painted triangles from the generated LODs — for geometry that is never visible. Removed geometry does not count towards the measured error.

For a worked example see Removing geometry that is never visible.