The term "magic box" refers to one of the less-known peculiarities of StarCraft's game engine that allows for high level execution when understood properly. In StarCraft, a group of units will maintain formation depending on how far apart they are from each other. Said simply, if you keep your units close enough, they will stay in formation, move in formation, and cast spells in formation. If your units are too far apart, they will lose formation, converge onto one location, and try to cast spells on the same location.
Sometimes you want a group of units to stay in formation, such as when blanketing the screen with Psionic Storms or when laying fields of Spider Mines. In other occasions, it may be optimal for units to clump as closely as possible -- for example, Mutalisk harassment.
How it works
The following will explain how to keep your units and cast spells in formation.
Fixed magic box
The fixed magic box is the maximum distance your units can be from each other and still stay in formation when you issue an order. The size of this box is hardcoded into StarCraft and varies for air and ground units.
- Ground - 195 x 195 pixels
- Air - 255 x 255 pixels
Use the picture for reference.
Note that not all the units have to fall entirely within the magic box, they just have to able to be selected within the magic box.
Minimum unit selection box
This box is the smallest possible rectangle that can select all your units. In order for units to stay in formation, you must issue an order outside the minimum unit selection box. If, for example, a move command is issued inside this minimum unit selection box, the units will break formation and form into a tighter ball.
Note that the box does not necessarily have to be a square. Once again not all units have to entirely fall within the box, just enough so the units can be selected.
- Make sure your units lie within the fixed magic box.
- Issue your command outside the minimum unit selection box.
Staying in formation
- Casting Psionic Storm
- Casting Disruption Web
- Laying Spider Mines
- Multiple transport drop
- Mutalisk harass
- Wraith harass