CPU

Pico-8 keeps track of CPU usage using two values: a Lua instruction usage, and a system usage.

The function stat(1) returns the total (Lua + system) usage for the current frame, and stat(2) returns the system usage.

Only a few functions have a system usage, measured in ticks. There are 4194304 ticks in a second (2^22), so about 69905 ticks per frame at 60 FPS.

Functions with a system cost

Function	Ticks	Notes
cls()	1024	same cost as rectfill of same size
print()	2+n*8	n is the number of characters in the string, even those not rendered spaces, newlines, and double-width glyphs each count as one character
spr()	n	n is the number of pixels drawn, including transparent pixels (width × height of the sprite rectangle) cost is 0 if first argument is outside the [0, 255] range
sspr()	n	n is the number of pixels drawn, including transparent pixels (width × height of the destination rectangle)
rect()	max(1,2*ceil(a/4)) + max(0,2*ceil(b/2-1))	Where: w,h = abs(x2-x1),abs(y2-y1) a,b = max(w,h),min(w,h)
rectfill()	max(1,flr(n/16))	n is the number of pixels drawn (width × height)
circ()	2+n*4	warning: that formula is incomplete for clipped circles
circfill()	n*flr((n+9)/4)	warning: that formula is incomplete for clipped circles
line()	ceil(n/2)	n is the number of pixels drawn; there is an additional cost of 1 if at least one pixel had to be clipped
map() / mapdraw()	max(1,n*64)	n is the number of sprites rendered; only cells that are not zero in the map are considered
music()	16	no cost if no argument
sfx()	16	no cost if no argument
memcpy()	n+1	n is the number of bytes copied
memset()	max(1,ceil(n/2))	n is the number of bytes set
reload()	max(1,n*8)	n is the number of bytes reloaded
btn()	4	no cost if no argument
btnp()	4	no cost if no argument
rnd()	4
sqrt()	24	only 16 if argument is zero
stat()	16