Advanced Mesh Hiding
The Advanced Mesh Hiding is a feature implemented in UMA 2.7 to allow a wardrobe recipes to specify exactly which triangles of a given slot will be hidden during generation. This is to allow much more freedom over when and which parts of a mesh are hidden.
Mesh Hide Asset
To create a new Mesh Hide Asset, right mouse click in your project folders, select Create -> UMA -> Misc -> Mesh Hide Asset.
Once a new Mesh Hide Asset is created it takes a slot as an input. Selecting a slot will display the slot and it's current triangle mask in the model viewer and allow you to select the "Begin Editing" button to go to the editing scene.
Adding to Wardrobe Recipe
Once a Mesh Hide Asset is created and ready, to use it, it will need to be added to a wardrobe recipe. It is simply added to the "Mesh Hide Assets" list found in wardrobe recipes. This effectively means, when this wardrobe recipe is active on the UMA and the slot in the Mesh Hide Asset is found, then apply the triangle masking set up in the Mesh Hide Asset.
Once you are ready to create the masking selection for a Mesh Hide Asset, select the asset and click "Begin Editing". A pop-up warning will let the user know to save the current save and change to a new empty scene with just the slot from the Mesh Hide Asset.
The editing scene will present a mesh of the intended slot for the user to select ("Colored red") triangles that indicate to be hidden at runtime. There are several options to aid the user in making these selections.
Clear: clear the entire selection.
Select All: select all triangles.
Invert: invert the current selection.
The user can also click and drag to select multiple triangles with a selection box, hold shift and left click to "paint" selecting and hold alt to orbit.
Choose "Select" or "UnSelect" to change what mode of selection you are in.
Show Wireframe: Toggle wireframe on or off.
Backface Cull: Toggle whether to select or unselect triangle facing away from the camera or not.
Focus Mesh: Focus the camera on the mesh.
Save & Return: Save the current selection and return to the previous scene.
Cancel Edits: Don't save the changes to the selection and return to the previous scene.
In the inspector are a couple advanced tools.
First is an optional occlusion slot. Select another slot and the wireframe mesh will be shown over the current mesh. You can scale it outwards along it's normal using the "occluder offset".
Select "Raycast Hidden Faces" to have the system attempt to automatically figure out with triangles are occluded by the selected occlusion slot.
The second option is to set selected triangles from a grayscale image of the uv map. For each triangle's center pixel, if the grayscale value is above 0.5 then the triangle is selected otherwise it is set as not selected.