Size & Copies (NUSIZ)#

There are only two players, but a single register stretches what they can do. NUSIZ0 and NUSIZ1 (one per player) set a player’s width and let the TIA stamp out multiple copies of it across the line — and the same register sizes that player’s missile. It’s the cheapest way to get more than two objects on screen at once.

Player width and copies#

The low three bits of NUSIZ choose one of eight modes:

Value	Player drawn as
0	one copy, normal width (8 px)
1	two copies, close together
2	two copies, medium gap
3	three copies, close
4	two copies, wide gap
5	double width (one copy, 16 px)
6	three copies, medium gap
7	quad width (one copy, 32 px)

Two ideas in one register: scaling (modes 5 and 7 stretch the same 8-bit bitmap to 2× or 4×) and replication (the copy modes draw the identical bitmap two or three times across the scanline, from one GRP0 write).

The copies are the trick behind rows of identical objects — the marching aliens of Space Invaders, a line of bricks, a set of pips — all from a single player you’d otherwise be able to show only once. From a single GRP0 write the copies are identical — each shares the player’s graphics, color, and any reflection. But because the copies sit at different points along the line, the beam reaches them at different moments, so rewriting GRP0 in the cycle gap between copies gives each one its own bitmap (or a blank). That mid-line trick is how Space Invaders makes its six-across aliens differ, animate, and wink out individually when shot.

Missile width#

The same register sizes the matching missile through its high bits: missile m can be 1, 2, 4, or 8 color clocks wide. A 1-clock missile is a thin bullet; an 8-clock one is a fat block. (More on missiles in Missiles & the Ball.)

In Practice#

Copies are the poor player’s sprite multiplier. Need three evenly-spaced identical shapes on a line? One player in a 3-copy mode beats juggling sprites. Their graphics can still differ via mid-line GRP0 rewrites (above), but their spacing and motion can’t — copies are locked to the fixed NUSIZ gaps and move as one. The instant the objects need independent positions or motion, you’re back to two players plus multiplexing.
Quad-width players make big, coarse shapes cheap. A 4× player is 32 pixels wide from one bitmap — good for banners, title text built from player-as-digit graphics, or a large boss, at the cost of chunky pixels.
NUSIZ changes can be timed mid-line, like any register — advanced kernels switch sizes within a frame, though the retiming has its own quirks best left until you’re comfortable with steady-state sprites.