The donut button appears only in physical mode. It is used to create a ring-like polygon. The number of segments used to approximate a circle can be altered with the sides command.
If the user presses and holds the Shift key after the center location is defined, and before the perimeter is defined by either lifting button 1 or pressing a second time, the current radius is held for x or y. The location of the Shift press defines whether x is held (pointer closer to the center y) or y is held (pointer closer to the center x). This allows elliptical donuts to be generated. This similarly applies when defining the outer radii, so that the inner and outer surfaces can have different elliptical aspect ratios, though the outer radius must be larger than the inner radius at all angles.
The Ctrl key also provides useful constraints. Pressing and holding the Ctrl key when defining the radii produces a radius defined by the pointer position projected on to the x or y axis (whichever is closer) defined from the center. Otherwise, off-axis snap points are allowed, which may lead to an unexpected radius on a fine grid.
When the command is expecting a mouse button press to define a radius, the value as defined by the mouse pointer (in microns) is printed in the lower left corner of the drawing window, or the X and Y values are printed if different. Pressing Enter will cause prompting for the value(s), in microns. If one number is given, a circular radius is accepted, however one can enter two numbers separated by space to set the X and Y radii separately.
While the command is active in physical mode, the cursor will snap to horizontal or vertical edges of existing objects in the layout if the edge is on-grid, when within two pixels. When snapped, a small dotted highlight box is displayed. This makes it much easier to create abutting objects when the grid snap spacing is very fine compared with the display scaling. This feature can be controlled from the Edge Snapping group in the Snapping page of the Grid Setup panel.
If the SpotSize variable is set to a positive value, or the MfgGrid has been given a positive value in the technology file, tiny round and donut figures are constructed somewhat differently. the figure is constructed somewhat differently. Objects created with the round and donut buttons will be constructed so that all vertices are placed at the center of a spot, and a minimum number of vertices will be used. The sides number is ignored. This applies only to figures with minimum radius 50 spots or smaller; the regular algorithm is used otherwise. An object with this preconditioning applied should translate exactly to the e-beam grid. See E.11 for more information.