How to use PLink
PLink draws piecewise linear link projections. Components may be
points, PL arcs, or PL circles. Line segments are oriented consistently in
each component. Different components are different colors.
Drawing Basics
- When using the mouse to draw a link with PLink, you should always
click-and-release. Do not hold the mouse button down while drawing.
PLink requires only the left mouse button.
- The default state of the editor is indicated by the arrow cursor.
In this state, click-and-release the left mouse button on the
background to place a starting vertex and begin drawing. The vertex
will be connected to the pencil cursor by a thin red line.
Click-and-release to place a second vertex. The two vertices will
then be joined by an edge. Continue to draw other vertices and edges
to your heart’s content.
- To stop drawing, either click twice on the same vertex to create an
arc, or click on an endpoint vertex. The latter operation will
either create a circle component or join together two arc
components.
- When the cursor hovers over a vertex it changes to the pointing
finger. From this state you can drag a vertex to a new location
with a click-and-release on the vertex. The vertex will become
enclosed in a circular cursor. Move it to where you want it to go
and click the left (or middle) button to place it. If you drag one
endpoint on top of another, they will meld.
- When the cursor hovers over an edge, not too close to a vertex or
crossing, it changes to the push-me-pull-you cursor. Clicking in
this state will change the orientation of the component containing
the edge.
- When the cursor hovers over a crossing it changes to the yin-yang
recycling cursor. Clicking while in this state changes the the
handedness of the crossing.
- Double-clicking on an endpoint vertex will restart drawing from
that vertex. Double-clicking on a non-endpoint vertex will break
the link at that point and begin drawing with the old incoming edge.
- You will not be allowed to create edges that pass too close to a
vertex or a crossing, or to place vertices too close to edges or to
crossings or to other vertices. If you attempt to do any of these
things, PLink will beep at you.
Miscellaneous Features
The window can be resized to allow for different sizes of link
projections, and the arrow keys can be used to slide the projection
around in order to make more room on one side or another.
The “Tools” menu can be used to make the projection alternating
(provided that all components are circles), or to clear the screen,
or to reflect the projection in the xy-plane, changing all crossings.
The “File” menu can be used to save the projection as a SnapPea
link projection file. (This can be done from the drawing state as
well, in which case the “hot vertex” is remembered in the file!). The
“File->Open File” command will read a SnapPea link projection file,
and restart drawing if the projection was saved while drawing. The
“Info” menu allows an encoding of the link projection to be printed
in the info line at the bottom. Various encoding schemes for link
projections are supported. Cutting and pasting from the info line
is possible.
If you are running PLink from inside SnapPy, closing the
window or exiting the program will pass your projection to SnapPy to
have its complement triangulated.