The round button, only available in physical mode, will create a disk object. The number of sides 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 objects to be generated.
The Ctrl key also provides useful constraints. Pressing and holding the Ctrl key when defining the radius 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.
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 with the edge snapping menu in the Cursor Modes panel, or by setting the EdgeSnapMode variable.
If the SpotSize variable is set to a value (with the !set command), the figure is constructed somewhat differently. With the SpotSize variable set to a positive value, objects created with the round and donut buttons will be created 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. This conditioning, with SpotSize set nonzero, applies only to objects created with the round and donut commands, and not the arc command or general polygons.