The polyg button is used to create and modify polygons. In electrical mode, this functionality is available from the poly menu selection brought up by the shapes button. A polygon is created by clicking the left mouse buton on each vertex location in sequence. The vertices can be undone and redone with the Tab key and Shift-Tab combination, which are equivalent to the Undo and Redo commands. Vertex entry is terminated, and a new polygon potentially created, by clicking on the initial point (marked with a cross), or double-clicking the last point, or by pressing the Enter key. At least three distinct vertices must have been defined, and the polygon must pass some ``normality'' tests, for successful object creation.
The PixelDelta variable can be set to alter the value, in pixels, of the snap distance to the target when clicking to terminate. By default, the snap distance is 3 pixels, so clicking within this distance of the initial point will terminate entry rather than add a new vertex.
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 is also applied to the first vertex of polygons being created, facilitating point list termination. This feature can be controlled from the Edge Snapping group in the Snapping page of the Grid Setup panel.
When adding vertices during polygon creation, the angle of each segment can be constrained to a multiple of 45 degrees with the Constrain angles to 45 degree multiples check box in the Editing Setup panel from the Edit Menu, in conjunction with the Shift and Ctrl keys. There are three modes: call them ``no45'' for no constraint, ``reg45'' for constraint to multiples of 45 degrees with automatic generation of the segment from the end of the 45 section to the actual point, and ``simp45'' that does no automatic segment generation. The ``reg45'' algorithm adds a 45 degree segment plus possibly an additional Manhattan segment to connect the given point. The ``simp45'' adds only the 45 degree segment. The mode employed at a given time is given by the table below. The Constrain45 boolean variable tracks the state (set or not set) of the check box.
|Constrain45 not set|
|Shift up||Shift pressed|
|Shift up||Shift pressed|
In physical mode, a new polygon is tested for reentrancy and other problems, and a warning message is issued if a pathology is detected. The new polygon is not removed from the database if such an error is detected. It is up to the user to make appropriate changes.
In electrical mode, if the current layer is the SCED layer, the polygon will be created using the ETC2 layer, otherwise the polygon will be created on the current layer. It is best to avoid use of the SCED layer for other than active wires, for efficiency reasons, though it is not an error. The Change Layer command in the Modify Menu can be used to change the layer of existing objects to the SCED layer, if necessary. The outline style and fill will be those of the rendering layer. Polygons have no electrical significance, but can be used for illustrative purposes.