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Polygonal objects

There are two kinds of polygonal objects. The difference between a line object and a polygon object is that the boundary of a polygon is drawn--if it is drawn--as a closed curve, while a line object has an open polygonal chain as boundary. Furthermore, line objects can have arrows, while polygons cannot. There is no difference between line and polygon objects with stroke color empty and without arrows.

  Both types of objects can be filled, but the versions of Ipe based on the GL library can only show this correctly on the screen if the polygon is simple, that is if it does not have any self intersections. In that case, use the previewer to view what you are doing, or switch to the pure X version of Ipe.

  When you create a line object, it will only have its stroke color set, even if the current fill color is not empty. (However, if the current stroke color is empty and the fill color is not, it will be filled.) If you want a filled line object, you have to do so explicitly by clicking in the color window with the left mouse button. Polygon objects are a bit more complicated. By default, when you create a polygon object, it will have both its stroke and its fill color set to the current settings. Sometimes, however, the following alternative behavior is more desirable. When the current fill color is not empty, the object is created filled, but without boundary. To draw the boundary, you have to explicitly request it by clicking with the middle mouse button in the color window. This alternative behavior can be requested by setting the button Stroke in the configuration panel to off.

  Existing polygonal objects can be edited, using Ipe's edit mode. You select the object you want to modify, and then press M-e (or select edit from the struc menu). The object will be placed in edit mode.

After selecting a polygonal object (a line or a polygon), and typing M-e, it is outlined with its vertices marked by little squares. In this mode, there is always a selected vertex, shown by a little circle around it. Using the right mouse button, a different vertex can be selected. The middle mouse button first selects and then moves a vertex. The left mouse button inserts a vertex at the mouse position. This new vertex appears in the polygonal chain after the selected vertex. Since it is not always clear how a polygonal chain is oriented, the segment of the polygonal chain where a new vertex would be inserted is shown dashed. To add vertices at the end of the polygonal chain, first select the last vertex of the chain with the right mouse button. The direction of the chain can be reversed by pressing r in edit-mode. This is useful to insert vertices in front of an existing polyline. Using the C-d or C-h key, the selected vertex can be removed. Finally, you leave the edit mode using the M-e key.


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