Relief only. Displays relief maps only, in the viewport.
Flat shade. Displays a flat shaded view, in the viewport.
Specular only. Displays only your specular maps, in the viewport.
Show displaced mesh. Show actual mesh displacement - vertices of the mesh will be displaced along the normal in correspondence with the displacement map.
Wireframe. Show wireframe of the model.
Low-poly. View and edit low-poly model with normal map.
Smooth Shade. Smooth shade (hotkey “5”).
Low Smooth Shade. Low Smooth Shade (hotkey “7”).
Environment Shade. This is default. It will display all maps you have applied, in the viewport.
Grid. Turn on/off 3D-grid plane in 3D viewport.
Axis. Show/hide axis.
Grid 2D mode. Turn on/off 2D grid of screen.
Snap to low-poly vertices. Snaps your pen to low-poly vertices. Sometimes helpful when you are etopologizing, or texturing.
Orthographic Projection. Toggle perspective/orthogonal projection.
Adjust subpatching. You can improve the visual appearance of mesh displacement using subpatches. Subpatching is a grid NxN over every face. Use this options only is you are sure that your video card is strong enough.