###########################################
#
#  Keyboard Test
#
#  A simple live display of which CHIP-8
#  keys appear to be held down at any given time.
#  useful for testing alternative Keyboard
#  layouts or input routines.
#
###########################################

: held    0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
: keymap  0x1 0x2 0x3 0xC 0x4 0x5 0x6 0xD 0x7 0x8 0x9 0xE 0xA 0x0 0xB 0xF
: button  0x7E 0xFF 0xFF 0xFF 0xFF 0xFF 0x7E

: main
	:const cell 8
	:calc start-x { 2 + 32 - ( cell * 4 ) / 2 }
	:calc start-y { 1 + 0 }
	:calc end-x   { start-x + cell * 4 }
	:calc end-y   { start-y + cell * 4 }
	
	v1 := start-x
	v2 := start-y
	v3 := 0
	loop
		i := keymap
		i += v3
		load v0
		i := hex v0
		sprite v1 v2 5
		v1 += cell
		if v1 == end-x then v2 += cell
		if v1 == end-x then v1 := start-x
		v3 += 1
		if v3 != 16 then
	again
	
	loop
		# unroll this loop fully to try to
		# minimize input lag:
		:macro scan {
			:calc keycode  { @ keymap + CALLS }
			:calc heldaddr { held + CALLS }
			:calc kx       { -2 + start-x + cell * floor CALLS % 4 }
			:calc ky       { -1 + start-y + cell * floor CALLS / 4 }
			v1 := keycode
			v2 := kx
			v3 := ky
			i  := heldaddr
			load v0
			if v0 == 0 begin
				if v1 key begin
					v0 := 1
					i := button
					sprite v2 v3 7
				end
			else
				if v1 -key begin
					v0 := 0
					i := button
					sprite v2 v3 7
				end
			end
			i := heldaddr
			save v0
		}
		scan scan scan scan
		scan scan scan scan
		scan scan scan scan
		scan scan scan scan
	again