-Added Mouse-based panning and changed zoom to focus on viewport center instead of top-left.
-Added Length to the first 1/8th of the circle block segments
Switched the way the grid is drawn, added panning/zoom support This fix should make this run a lot faster and also means you don't need to depend on the browser's built in zoom feature.
Slopes now mirror correctly on odd sized circles. There is still an occasional bug where the 4 "corner" slopes will draw or not draw at the wrong times.
Next step is to support exporting images to .png/.jpg and fixing that.
Mirrored the slopes around the entire circle and slightly tweaked.
Still need to fill in the "corner spots" and fix slopes mirroring on odd diameter circles.