mathr / blog / #

Konstrukt is an SVG + ECMAScript application for compass and straightedge construction. It's not too unintuitive to use, once you know what the controls are:

to draw a straight line through two marked points

press the v key and click on the two points

to draw a circle centered at one marked point through another

press the c key and click on the two points (the first of which is the center)

to delete a marked point and all edges through it

press the x key and click on the point (tip: you might create extra lines and circles for the purposes of deleting at an intersection)

to move the viewpoint

click on empty space to center the view on that position

to zoom in

press the PgUp key

to zoom out

press the PgDn key

Further to the basic construction commands, you can highlight parts of the drawing:

to change the highlight stroke thickness

press the - key or the + key

to change the highlight fill colour for future polygons

press the [ key or the ] key

to highlight a line segment between two marked points

press the s key and click on the two end points

to highlight an arc between three marked points

press the a key and click on the center and two end points, the arc will be drawn anti-clockwise

to highlight a filled polygon

press the f key and click on as many points as you like, then click on the first point again to finish

You can also toggle the visibility of the construction points (but not the highlights) using the h key. The image above was created in GIMP from two screenshots, one with construction lines and one with them hidden.

This version 3 is from March 2010, but I didn't get around to posting it anywhere until now. There are some internal code changes for efficiency and maintainability, too.