Draw:

• Left Mouse -> Draw
• Right Mouse -> Erase
• Shift + Left Mouse -> Draw Line
• Ctrl + Left Mouse -> Draw Rectangle
• G + Left Mouse -> Draw Grid
• 1/2/3/4/5/6/7 -> White/R/G/B/C/Y/M

Camera:

• Scroll -> Zoom
• Shift Scroll -> Zoom + Change brush size
• Ctrl Scroll -> Change brush size
• Middle Mouse or Space -> Pan

Other:

• Z -> Undo
• R -> Reset
• Grag & drop images