Persp/Ortho 

Switch between Perspective and Orthographic projection.

Up X/Y/Z/Free 

Select the "Up" axis for the loaded mesh. By default its Z-up, which is standard among CAD applications, but many popular animation programs use Y-up. So if you load your mesh and its lying on its side, try the Y-up or X-up options to get it up the right way. The Free option turns on free rotation; UVLayout won't try and keep the object upright, and so you can tumble the view beyond the normal camera lock points.

Light Slider 

Move the slider to move the light source from right to left. Click the gray Light button to cycle between four different levels of ambient lighting, from none to full and a couple of levels in between. The default is a small amount of ambient lighting.

X-Ray Slider 

Move the slider to the left to make the mesh more and more transparent. You can use this see, and pick, obscured edges that might be hard to access normally.

View UV/Ed/3D 

Switch between UV edit, 3D edit and 3D textured views. Use the ? hotkey to find out what other hotkeys are available in each mode.

Color Error / 4/5 / Local 

Switch between "flattening error" and 4/5 keys or Local "rescale" coloring of polys when in the UV view.

Scale 

Adjust this to make the error and scaling coloring more or less visible.

Trace 

Click the Trace button to show an image in the background when editing UVs. Use the first slider to fade the background in and out, and the second slider to change the transparency of the flattened geometry. The loaded image will also display mapped onto the mesh in the 3D view as one of the T hotkey texture cycles. Once loaded, click Trace to toggle the texture on and off.

To change the loaded image, move the mouse pointer to the top right of the 0 to 1 tile and a checker icon and the name of the loaded file will appear. Click the checker icon to select a different file.

You can also move the mouse pointer to the top right of any other tile to load an additional image into just that single tile.

Show Repeats 

Ticking this will draw ghost copies of the visible shells into surrounding tiles. It will also change the behavior of the Render tool, outputting just the single 0 to 1 tile, but wrapping the graphics around for shells that extend beyond that tile. And finally the tile coverage feedback operates in the same way, showing the stats for just the 0 to 1 tile, but accounting for shells that wrap around.

Show Poly Outlines 

Shows the polygon outlines when the mesh is drawn in the T hotkey textured 3D views.

Hide Seams in 3D 

Hides the green UV seam lines when the mesh is drawn in the 3D view.

Cull Backfaces 

Hides backfacing polys from the 3D views. For example, if you are editing a scene that consists of geometry inside a closed room, ticking this option will allow you to see the internal geometry easily (i.e. the front walls will be hidden).

Fade Short Edges 

Fade out then hide the wire lines for very short edges. Especially useful when editing dense meshes, as it allows you to see more clearly the color feedback shading on polygons.

Sync Ed & 3D Views 

If you move the camera in an Ed or 3D view, then all other cameras to these spaces will move as well.

Normals Smooth/OBJ 

When shading the mesh with the T hotkey texturing, use average smooth normals, or normals imported from the OBJ file (if any are defined).

Show Udim / U,V 

Ticking either of these will display the tile numbers in the UV view.

Max U 

Where tile udims are displayed or used in any way, this preference selects how those tile numbers are calculated. The first setting is the maximum number of columns, and the default of 10 is the industry standard. The second setting is the number of the first unit tile, and 1001 again is the standard value, but can be changed if required.

1st UV 

Where tile U and V values are displayed or used, this preference selects what numbers are given to the first unit tile.

Go To 

Type a Udim value or U and V value here, followed by the Enter key, and the view will zoom to that tile.

Panes

Split Pane 

This splits the current pane into two. If you only have the single view window up, it'll create two equal sized panes within that space. Initially the newly split panes have the exact same view, but you can use the 1, 2 or 3 hotkey at any time to change a pane's view mode. The view mode of each pane is shown in the title bar.

Kill All Panes 

You can kill individual panes by clicking on the X at the top right of the pane frame, but if you want to get rid of them all at once, click this button. It will take you back to the default single view window.

Moving and Resizing 

To move a pane within the window, LMB click'n'drag any part of the pane frame or title bar. To resize a pane, LMB click'n'drag either of the bottom left or right corners. To make a pane temporarily full size, click the square icon towards the top right of the pane frame.

Saving Panes 

If you have an arrangement of panes that you would like to use every time you run UVLayout, click the grey "pin" button to the left of the main GUI window About UVLayout button. This will save the pane positions and view modes, any they will be restored whenever you load a new object into UVLayout.