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 turn the directional light source on and off. When off, all faces are equally lit, making details in previously dark areas more visible.

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.

Trace 

Select Trace to load 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. Select Trace a second time to turn the background image off.

Smooth SUBD UVs  [Professional Version Only]  

When turned off, UVs are linearly subdivided when SUBD surfaces are displayed in smooth shading mode. When turned on, UVs are smoothly subdivided; this is equivalent to Renderman's Smooth UVs option. This toggle only applies to the display of textures, and doesn't affect the flattening in any way.

Show Repeats 

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. 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 box 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.