[key]: function (default)  // comment

-------------------------------------
[space]: Color Selector (off)  // just like the one in "Processing->Tools"
	[space]: OK
	[delete]: Cancel
[a]: Anti-aliasing (off)  // utilizing Anti-aliasing Lines algorithm in the lecture slides

[l]: Poly-line (on)  // drag mouse to simulate, and release mouse to draw
	[r]: Reset
	[c]: Encircle  // draw a line between the first and last points of the current poly-line
[p]: Pencil (off)  // draw by dragging mouse
[b]: Airbrush (off)  // utilizing Flood Fill algorithm in the lecture slides (please test it on small area since recursion takes time...)
[k]: Pick Color (off)  // pick color from canvas

[1]: Pen Size--1px (on)
[2]: Pen Size--3px (off)   
[3]: Pen Size--5px (off)
[4]: Pen Size--7px (off)
[9]: Pen Type--project (off)
[0]: Pen Type--round (on)

[w]: Rainbow (off)  // change color automatically when drawing
[i]: Invert  // invert every pixel's color on canvas

[h]: Help (off)
[n]: New
[s]: Save  // save to Sun_HW1.png
[o]: Open  // open Sun_HW1.png
[q]: Quit
-------------------------------------

Everything is drawn by point(). Enjoy it!