Game 2Unit 15 of 191 hr learning time
Mood through Constraint
The lighting engine is built; now compose with it. Give each room its own falloff — one byte — so the Hall reads as a broad lit chamber and the Vault as a near-black crypt lit only at the altar. Same two colours, same dither; restraint is the technique.
79% of Shadowkeep
The keep is lit and furnished — but every room is lit the same. A grand hall and a burial crypt should not feel alike, and atmosphere is as much about restraint as addition. This unit stops adding features and starts composing with the ones we have. The whole palette is still two colours a cell and a ramp of dither; the art is in how we use the limit.
The lever is a single byte per room: how fast its light fades.
What you’ll see by the end
The Vault, now: a single flame on the altar, a tight pocket of light around it, and beyond that darkness — the dither thickening to near-black across the floor, the walls swallowed. The coins and the Warden are faint shapes down in the gloom, the thief drawn toward the only light there is. Step back into the Hall and it’s the opposite: a wide, even glow, an open and unthreatening room. Two rooms, one lighting engine, two completely different feelings.
One byte of mood
Back in Unit 13 every room halved the distance to get its shade (distance >> 1). The new idea is to make that shift a property of the room — its falloff:
room_falloff:
defb 2 ; Hall — distance >> 2: a broad, soft pool
defb 1 ; Gallery — distance >> 1: medium
defb 0 ; Vault — distance : a tight pool, deep darkA bigger shift makes distance grow slowly, so the light reaches far — a generous, well-lit room. A shift of zero lets distance count cell-for-cell, so the light collapses to a tight ring and everything past it is black. shade_for_cell just reads the current room’s falloff and shifts by it:
ld a, (current_room)
; ... index room_falloff ...
ld b, (hl) ; B = this room's falloff
ld a, e ; A = distance to the torch
.sf_shift:
dec b
jr z, .sf_clamp
srl a ; shift by falloff, then clamp
jr .sf_shiftThat’s the entire mechanism. The Hall is welcoming and the Vault is oppressive because of one number each.
Composing the dark
Mood isn’t only the falloff — it’s where the light is. The Hall’s torch sits high in a wall, washing the room; the Vault has no wall torch at all. Its only flame is on the altar itself:
defb "#.............#T##.............#" ; a flame set in the altarSo in the Vault the light is born at the thing you’re meant to look at, falls off at once (falloff 0), and leaves the rest to the dark. The eye has nowhere to go but the altar — and the coins and the Warden you must read there are half-swallowed by the black, which is exactly the tension a crypt should have. That’s composition: not “make it bright” or “make it dark”, but put the one light where it means something and let the constraint do the rest. The Spectrum’s two-colour cell, which looked like a limitation in Unit 1, is now the instrument.
Milestone — a mood per room
The shift that used to be fixed (distance >> 1 everywhere) becomes a per-room
falloff byte: shade_for_cell reads the current room’s falloff and shifts the
distance by that many places. A big shift reaches far (the Hall, falloff 2); a shift
of zero collapses the light to a tight ring (the Vault, falloff 0, its only flame on
the altar). The whole composition is one number per room.
Step 1: a per-room falloff byte drives the shade ramp
+28-5
| 1 | 1 | ; Shadowkeep — Unit 15: Mood through Constraint | |
| 2 | 2 | ; Cumulative build; every step runs on its own. Narrative: the unit page. | |
| 3 | - | ; step-00 = Unit 14's end: lit and furnished, but every room lit the same. | |
| 3 | + | ; step-01 gives each room its own falloff — the Hall broad, the Vault a tight crypt. | |
| 4 | 4 | | |
| 5 | 5 | org 32768 | |
| 6 | 6 | | |
| ... | |||
| 192 | 192 | ; (lightest); far away = 4 (darkest). No torch = darkest everywhere. | |
| 193 | 193 | ; ---------------------------------------------------------------------------- | |
| 194 | 194 | shade_for_cell: | |
| 195 | + | push bc | |
| 195 | 196 | ld a, (torch_col) | |
| 196 | 197 | cp NO_TORCH | |
| 197 | 198 | jr z, .sf_dark | |
| ... | |||
| 212 | 213 | jr nc, .sf_max | |
| 213 | 214 | ld a, d | |
| 214 | 215 | .sf_max: | |
| 215 | - | srl a ; distance / 2 | |
| 216 | + | ld e, a ; E = Chebyshev distance | |
| 217 | + | ld a, (current_room) ; shift it by THIS room's falloff | |
| 218 | + | ld c, a | |
| 219 | + | ld b, 0 | |
| 220 | + | ld hl, room_falloff | |
| 221 | + | add hl, bc | |
| 222 | + | ld b, (hl) ; B = this room's falloff | |
| 223 | + | ld a, e | |
| 224 | + | inc b | |
| 225 | + | .sf_shift: | |
| 226 | + | dec b | |
| 227 | + | jr z, .sf_clamp | |
| 228 | + | srl a | |
| 229 | + | jr .sf_shift | |
| 230 | + | .sf_clamp: | |
| 216 | 231 | cp MAX_SHADE + 1 | |
| 217 | 232 | jr c, .sf_done | |
| 218 | 233 | ld a, MAX_SHADE | |
| 219 | 234 | .sf_done: | |
| 235 | + | pop bc | |
| 220 | 236 | ret | |
| 221 | 237 | .sf_dark: | |
| 222 | 238 | ld a, MAX_SHADE | |
| 239 | + | pop bc | |
| 223 | 240 | ret | |
| 224 | 241 | | |
| 225 | 242 | draw_room: | |
| ... | |||
| 741 | 758 | defb %01111110 | |
| 742 | 759 | defb %00111100 | |
| 743 | 760 | defb %00000000 | |
| 761 | + | | |
| 762 | + | ; One byte of mood per room: how slowly its light fades. | |
| 763 | + | room_falloff: | |
| 764 | + | defb 2 ; Hall — broad, soft pool | |
| 765 | + | defb 1 ; Gallery — medium | |
| 766 | + | defb 0 ; Vault — tight pool, deep dark | |
| 744 | 767 | | |
| 745 | 768 | ; The shade ramp: lightest (lit) to darkest (deep shadow), all blue/black dither. | |
| 746 | 769 | shade_tiles: | |
| ... | |||
| 1147 | 1170 | ; The Vault — a great altar of stone in the middle, south door (column 15) | |
| 1148 | 1171 | ; down to the Gallery. | |
| 1149 | 1172 | room2_template: | |
| 1150 | - | defb "###############T################" | |
| 1173 | + | defb "################################" | |
| 1151 | 1174 | defb "#..............................#" | |
| 1152 | 1175 | defb "#..............................#" | |
| 1153 | 1176 | defb "#..............................#" | |
| ... | |||
| 1157 | 1180 | defb "#..............................#" | |
| 1158 | 1181 | defb "#..............................#" | |
| 1159 | 1182 | defb "#..............................#" | |
| 1183 | + | defb "#.............#T##.............#" | |
| 1160 | 1184 | defb "#.............####.............#" | |
| 1161 | - | defb "B.............####.............#" | |
| 1162 | - | defb "#.............####.............B" | |
| 1185 | + | defb "#.............####.............#" | |
| 1163 | 1186 | defb "#.............####.............#" | |
| 1164 | 1187 | defb "#..............................#" | |
| 1165 | 1188 | defb "#..............................#" |
The complete program
; Shadowkeep — Unit 15: Mood through Constraint
; Cumulative build; every step runs on its own. Narrative: the unit page.
; step-01 gives each room its own falloff — the Hall broad, the Vault a tight crypt.
org 32768
WALL_ATTR equ %01001000
FLOOR_ATTR equ %00001000
MARK_ATTR equ %00001111
TORCH_ATTR equ %01001110 ; BRIGHT, blue paper, yellow ink — a lit sconce
STATUE_ATTR equ %01001111 ; BRIGHT white on blue — pale stone (solid)
BANNER_ATTR equ %01001011 ; BRIGHT magenta on blue — a hanging (solid)
RUBBLE_ATTR equ %00001000 ; dim, like floor — walkable broken stone
NO_TORCH equ $FF
MAX_SHADE equ 4
THIEF equ %01001010
GOLD_ATTR equ %00000110 ; yellow ink, no BRIGHT -> walkable gold
TOTAL_GOLD equ 6
WARDEN equ %01000101 ; BRIGHT cyan on black — the sentinel
WARDEN_COL0 equ 26 ; the Hall's gold column
WARDEN_ROW0 equ 11
WARDEN_SPEED equ 10 ; frames between patrol steps
WARDEN_GATHER equ 50 ; a beat before it begins to move
AXIS_HORIZ equ 0 ; the Warden varies its column (walks a row)
AXIS_VERT equ 1 ; the Warden varies its row (walks a column)
WALL_BIT equ 6
START_COL equ 15
START_ROW equ 11
NO_EXIT equ $FF
KEYS_OP equ $DFFE
KEYS_Q equ $FBFE
KEYS_A equ $FDFE
KEYS_SPACE equ $7FFE
start:
ld a, 0
out ($FE), a
im 1
; --- TITLE -> PLAY -> WIN -> TITLE ------------------------------------------
main_title:
call show_title ; returns (interrupts off) when SPACE pressed
call new_game ; reset the keep, place the gold, draw
ei
.game_loop:
halt
ld a, (won)
or a
jr nz, .won
call player_step
call warden_step ; every room has its Warden now
ld a, (caught)
or a
jr nz, .lost
call mark_step
jr .game_loop
.lost:
call show_lose ; "THE KEEP SLEEPS", the sting, wait for SPACE
jr main_title
.won:
call show_win ; "THE KEEP STANDS", flourish, wait for SPACE
jr main_title ; round again
; new_game — copy the room templates back into working state (so collected gold
; returns), reset the thief, the gold counter and the win flag, draw the keep.
new_game:
ld hl, room0_template
ld de, room0_state
ld bc, 768
ldir
ld hl, room1_template
ld de, room1_state
ld bc, 768
ldir
ld hl, room2_template
ld de, room2_state
ld bc, 768
ldir
xor a
ld (current_room), a
ld (won), a
ld (caught), a
ld a, TOTAL_GOLD
ld (gold_remaining), a
ld a, START_COL
ld (thief_col), a
ld a, START_ROW
ld (thief_row), a
call draw_room
call save_under
call draw_thief
call warden_enter ; this room's Warden, from the table
call save_warden
call draw_warden
ret
mark_step:
ld bc, KEYS_SPACE
in a, (c)
bit 0, a
ret nz
call cell_state_addr
ld (hl), '+'
ld hl, mark_tile
ld de, under_thief
ld bc, 8
ldir
ld a, MARK_ATTR
ld (under_thief + 8), a
ret
cell_state_addr:
call room_entry_addr
ld a, (hl)
inc hl
ld h, (hl)
ld l, a
push hl
ld a, (thief_row)
ld l, a
ld h, 0
add hl, hl
add hl, hl
add hl, hl
add hl, hl
add hl, hl
ld a, (thief_col)
ld e, a
ld d, 0
add hl, de
pop de
add hl, de
ret
room_entry_addr:
ld a, (current_room)
ld l, a
ld h, 0
ld d, h
ld e, l
add hl, hl
add hl, de
add hl, hl
ld de, rooms
add hl, de
ret
; ----------------------------------------------------------------------------
; find_torch — scan the current room's map for 'T', remember where it is (or
; NO_TORCH if the room is unlit).
; ----------------------------------------------------------------------------
find_torch:
ld a, NO_TORCH
ld (torch_col), a
ld (torch_row), a
call room_entry_addr
ld a, (hl)
inc hl
ld h, (hl)
ld l, a
ld b, 0
.ft_row:
ld c, 0
.ft_col:
ld a, (hl)
cp 'T'
jr nz, .ft_skip
ld a, c
ld (torch_col), a
ld a, b
ld (torch_row), a
.ft_skip:
inc hl
inc c
ld a, c
cp 32
jr nz, .ft_col
inc b
ld a, b
cp 24
jr nz, .ft_row
ret
; ----------------------------------------------------------------------------
; shade_for_cell — row in B, column in C. Returns a shade 0..4 in A: the
; Chebyshev distance to the torch, halved and clamped. Near the flame = 0
; (lightest); far away = 4 (darkest). No torch = darkest everywhere.
; ----------------------------------------------------------------------------
shade_for_cell:
push bc
ld a, (torch_col)
cp NO_TORCH
jr z, .sf_dark
ld a, b
ld hl, torch_row
sub (hl)
jr nc, .sf_rpos
neg
.sf_rpos:
ld d, a ; |row - torch_row|
ld a, c
ld hl, torch_col
sub (hl)
jr nc, .sf_cpos
neg
.sf_cpos:
cp d ; A = |dc|; max(|dc|, |dr|)
jr nc, .sf_max
ld a, d
.sf_max:
ld e, a ; E = Chebyshev distance
ld a, (current_room) ; shift it by THIS room's falloff
ld c, a
ld b, 0
ld hl, room_falloff
add hl, bc
ld b, (hl) ; B = this room's falloff
ld a, e
inc b
.sf_shift:
dec b
jr z, .sf_clamp
srl a
jr .sf_shift
.sf_clamp:
cp MAX_SHADE + 1
jr c, .sf_done
ld a, MAX_SHADE
.sf_done:
pop bc
ret
.sf_dark:
ld a, MAX_SHADE
pop bc
ret
draw_room:
call find_torch
call room_entry_addr
ld a, (hl)
inc hl
ld h, (hl)
ld l, a
ld (map_ptr), hl
ld b, 0
.room_row:
ld c, 0
.room_col:
ld hl, (map_ptr)
ld a, (hl)
cp '.'
jr nz, .not_floor
call shade_for_cell
add a, a
ld e, a
ld d, 0
ld hl, shade_tiles
add hl, de
ld e, (hl)
inc hl
ld d, (hl)
ld (tile_ptr), de
ld a, FLOOR_ATTR
ld (tile_attr), a
call draw_tile
jr .cell_done
.not_floor:
call lookup_tile
call draw_tile
.cell_done:
ld hl, (map_ptr)
inc hl
ld (map_ptr), hl
inc c
ld a, c
cp 32
jr nz, .room_col
inc b
ld a, b
cp 24
jr nz, .room_row
ret
lookup_tile:
ld hl, palette
.scan:
cp (hl)
jr z, .found
inc hl
inc hl
inc hl
inc hl
jr .scan
.found:
inc hl
ld e, (hl)
inc hl
ld d, (hl)
ld (tile_ptr), de
inc hl
ld a, (hl)
ld (tile_attr), a
ret
draw_tile:
push bc
call attr_addr_cr
ld a, (tile_attr)
ld (hl), a
call scr_addr_cr
ld de, (tile_ptr)
ld b, 8
.tile_row:
ld a, (de)
ld (hl), a
inc de
inc h
djnz .tile_row
pop bc
ret
player_step:
ld a, (thief_col)
ld (tcol), a
ld a, (thief_row)
ld (trow), a
ld bc, KEYS_OP
in a, (c)
bit 1, a
jr z, .left
bit 0, a
jr z, .right
ld bc, KEYS_Q
in a, (c)
bit 0, a
jr z, .up
ld bc, KEYS_A
in a, (c)
bit 0, a
jr z, .down
ret
.left:
ld hl, tcol
dec (hl)
jr .move
.right:
ld hl, tcol
inc (hl)
jr .move
.up:
ld hl, trow
dec (hl)
jr .move
.down:
ld hl, trow
inc (hl)
.move:
ld a, (trow)
ld b, a
ld a, (tcol)
ld c, a
call wall_at
ret nz
call restore_under
ld a, (tcol)
ld (thief_col), a
ld a, (trow)
ld (thief_row), a
call collect_gold ; the new cell might be gold — lift it first
call save_under
call draw_thief
call check_exit
ret
wall_at:
call attr_addr_cr
bit WALL_BIT, (hl)
ret
check_exit:
ld a, (thief_col)
or a
jr z, .west
cp 31
jr z, .east
ld a, (thief_row)
or a
jr z, .north
cp 23
jr z, .south
ret
.east:
call room_entry_addr
ld de, 4
add hl, de
ld a, (hl)
cp NO_EXIT
ret z
ld (current_room), a
ld a, 1
ld (thief_col), a
jr .enter
.west:
call room_entry_addr
ld de, 5
add hl, de
ld a, (hl)
cp NO_EXIT
ret z
ld (current_room), a
ld a, 30
ld (thief_col), a
jr .enter
.north:
call room_entry_addr
inc hl
inc hl
ld a, (hl)
cp NO_EXIT
ret z
ld (current_room), a
ld a, 22
ld (thief_row), a
jr .enter
.south:
call room_entry_addr
inc hl
inc hl
inc hl
ld a, (hl)
cp NO_EXIT
ret z
ld (current_room), a
ld a, 1
ld (thief_row), a
.enter:
call draw_room
call save_under
call draw_thief
call warden_enter ; this room's Warden, clear of the entry cell
call save_warden
call draw_warden
ret
pos_bc:
ld a, (thief_row)
ld b, a
ld a, (thief_col)
ld c, a
ret
save_under:
call pos_bc
call scr_addr_cr
ld de, under_thief
ld b, 8
.save_row:
ld a, (hl)
ld (de), a
inc de
inc h
djnz .save_row
call pos_bc
call attr_addr_cr
ld a, (hl)
ld (under_thief + 8), a
ret
restore_under:
call pos_bc
call scr_addr_cr
ld de, under_thief
ld b, 8
.restore_row:
ld a, (de)
ld (hl), a
inc de
inc h
djnz .restore_row
call pos_bc
call attr_addr_cr
ld a, (under_thief + 8)
ld (hl), a
ret
draw_thief:
call pos_bc
call attr_addr_cr
ld (hl), THIEF
call pos_bc
call scr_addr_cr
ld de, thief
ld b, 8
.thief_row:
ld a, (de)
ld (hl), a
inc de
inc h
djnz .thief_row
ret
; ----------------------------------------------------------------------------
; The Warden — something shares the keep. A second mover, drawn exactly like the
; thief: a private under-buffer and its own save / draw, a spectral hooded
; sentinel. First we simply give it a body (it neither moves nor harms yet).
; ----------------------------------------------------------------------------
wpos_bc:
ld a, (warden_row)
ld b, a
ld a, (warden_col)
ld c, a
ret
save_warden:
call wpos_bc
call scr_addr_cr
ld de, under_warden
ld b, 8
.svw_row:
ld a, (hl)
ld (de), a
inc de
inc h
djnz .svw_row
call wpos_bc
call attr_addr_cr
ld a, (hl)
ld (under_warden + 8), a
ret
draw_warden:
call wpos_bc
call attr_addr_cr
ld (hl), WARDEN
call wpos_bc
call scr_addr_cr
ld de, warden_glyph
ld b, 8
.drw_row:
ld a, (de)
ld (hl), a
inc de
inc h
djnz .drw_row
ret
; A spectral hooded sentinel: a cowl with dark eye-slits over a robe that frays
; at the hem. Cold, faceless, unmistakably a figure.
warden_glyph:
defb %00111100
defb %01111110
defb %01100110
defb %01111110
defb %00111100
defb %01111110
defb %01111110
defb %01011010
restore_warden:
call wpos_bc
call scr_addr_cr
ld de, under_warden
ld b, 8
.rsw_row:
ld a, (de)
ld (hl), a
inc de
inc h
djnz .rsw_row
call wpos_bc
call attr_addr_cr
ld a, (under_warden + 8)
ld (hl), a
ret
; warden_step — the patrol. Walks its column one cell every WARDEN_SPEED frames,
; after a WARDEN_GATHER beat, reversing at walls. Deterministic: a route you learn
; and time. It reads the thief's cell as a wall (his attribute has WALL_BIT set),
; so it turns aside at him for now — the catch is Unit 11.
warden_step:
ld a, (warden_timer)
dec a
ld (warden_timer), a
ret nz
ld a, WARDEN_SPEED
ld (warden_timer), a
; propose the next cell along the patrol axis, in the current dir
ld a, (warden_axis)
or a
jr nz, .ws_vert
.ws_horiz:
ld a, (warden_row)
ld b, a ; B = row (fixed)
ld a, (warden_dir)
ld hl, warden_col
add a, (hl)
ld c, a ; C = next col
jr .ws_have
.ws_vert:
ld a, (warden_col)
ld c, a ; C = col (fixed)
ld a, (warden_dir)
ld hl, warden_row
add a, (hl)
ld b, a ; B = next row
.ws_have:
ld a, b ; the thief there? caught — check BEFORE
ld hl, thief_row ; wall_at, because his own cell reads as wall
cp (hl)
jr nz, .ws_wall
ld a, c
ld hl, thief_col
cp (hl)
jr nz, .ws_wall
ld a, 1
ld (caught), a
ret
.ws_wall:
push bc
call wall_at
pop bc
jr z, .ws_commit ; floor ahead — step onto it
ld a, (warden_dir) ; wall ahead — reverse, wait a beat
neg
ld (warden_dir), a
ret
.ws_commit:
push bc ; keep the proposed (row B, col C)
call restore_warden
pop bc
ld a, c
ld (warden_col), a
ld a, b
ld (warden_row), a
call save_warden ; photograph the new cell's ground
call draw_warden
ret
; ----------------------------------------------------------------------------
; warden_enter — instantiate the current room's Warden from warden_table: place
; it at the route-start (chosen clear of the entry cell), set its axis, and start
; its gather. Called on new_game and on every room change. A second mover is a
; table entry — like the torches and the gold.
; ----------------------------------------------------------------------------
warden_enter:
ld a, (current_room)
add a, a
add a, a ; * 4 bytes per table row
ld e, a
ld d, 0
ld hl, warden_table
add hl, de
ld a, (hl)
ld (warden_col), a
inc hl
ld a, (hl)
ld (warden_row), a
inc hl
ld a, (hl)
ld (warden_dir), a
inc hl
ld a, (hl)
ld (warden_axis), a
ld a, WARDEN_GATHER
ld (warden_timer), a
ret
; warden_table — one row per room: start col, start row, dir (+1/-1), axis.
; Each route crosses that room's gold and starts clear of the entry cell.
warden_table:
defb WARDEN_COL0, WARDEN_ROW0, -1, AXIS_VERT ; Hall — the gold's column
defb 24, 15, -1, AXIS_VERT ; Gallery — column 24, lower chamber
defb 15, 20, -1, AXIS_HORIZ ; Vault — row 20, between the coins
; ----------------------------------------------------------------------------
; The gold — the keep's goal. Step onto a coin and it lifts: the map cell turns
; to floor (gone for good), the cell repaints as plain floor (no lighting yet),
; a chime sounds, and the counter ticks down.
; ----------------------------------------------------------------------------
collect_gold:
call cell_state_addr ; HL -> map cell at the thief's position
ld a, (hl)
cp 'G'
ret nz
ld (hl), '.' ; the gold is taken — floor from now on
call pos_bc ; B = row, C = col
call draw_floor_cell ; repaint the cell as plain floor
call sfx_pickup
ld hl, gold_remaining
dec (hl)
ld a, (hl)
or a
call z, win ; the last coin — the keep stands
ret
; draw_floor_cell — paint the floor tile at (row B, col C). Lighting (Unit 13)
; will replace this with a shade chosen by distance from the nearest torch.
draw_floor_cell:
call shade_for_cell
add a, a
ld e, a
ld d, 0
ld hl, shade_tiles
add hl, de
ld e, (hl)
inc hl
ld d, (hl)
ld (tile_ptr), de
ld a, FLOOR_ATTR
ld (tile_attr), a
call draw_tile
ret
; ----------------------------------------------------------------------------
; beep — the one tone primitive (the tiny game's blip, reused). B = cycles,
; C = the delay between speaker toggles (the pitch; larger C = lower).
; ----------------------------------------------------------------------------
beep:
.bp_cycle:
ld a, %00010000
out ($FE), a
ld e, c
.bp_hi:
dec e
jr nz, .bp_hi
xor a
out ($FE), a
ld e, c
.bp_lo:
dec e
jr nz, .bp_lo
djnz .bp_cycle
ret
; sfx_pickup — a bright two-blip chime: the sound of gold.
sfx_pickup:
ld b, 8
ld c, 20
call beep
ld b, 8
ld c, 14
call beep
ret
gold_tile:
defb %00000000
defb %00111100
defb %01111110
defb %01111110
defb %01111110
defb %01111110
defb %00111100
defb %00000000
; One byte of mood per room: how slowly its light fades.
room_falloff:
defb 2 ; Hall — broad, soft pool
defb 1 ; Gallery — medium
defb 0 ; Vault — tight pool, deep dark
; The shade ramp: lightest (lit) to darkest (deep shadow), all blue/black dither.
shade_tiles:
defw shade0_tile
defw shade1_tile
defw shade2_tile
defw shade3_tile
defw shade4_tile
shade0_tile: ; lit — nearly all blue
defb %00000000
defb %00100010
defb %00000000
defb %00000000
defb %00000000
defb %10001000
defb %00000000
defb %00000000
shade1_tile:
defb %00100010
defb %00000000
defb %10001000
defb %00000000
defb %00100010
defb %00000000
defb %10001000
defb %00000000
shade2_tile: ; the half-and-half slate from Unit 2
defb %10101010
defb %01010101
defb %10101010
defb %01010101
defb %10101010
defb %01010101
defb %10101010
defb %01010101
shade3_tile:
defb %10101010
defb %11111111
defb %01010101
defb %11111111
defb %10101010
defb %11111111
defb %01010101
defb %11111111
shade4_tile: ; deep shadow — nearly all black
defb %11111111
defb %11101110
defb %11111111
defb %10111011
defb %11111111
defb %11101110
defb %11111111
defb %10111011
torch_tile: ; a flame in its sconce
defb %00010000
defb %00111000
defb %00111000
defb %01111100
defb %01111100
defb %01111100
defb %00111000
defb %00010000
statue_tile:
defb %00111100
defb %01111110
defb %00111100
defb %00011000
defb %00011000
defb %00111100
defb %01111110
defb %01111110
banner_tile:
defb %01111110
defb %01111110
defb %01011010
defb %01011010
defb %01111110
defb %01111110
defb %00111100
defb %00011000
rubble_tile:
defb %00000000
defb %01100000
defb %01100000
defb %00000110
defb %00000110
defb %00011000
defb %00011000
defb %00000000
; ----------------------------------------------------------------------------
; show_title — black screen, the keep's name and a prompt; wait for SPACE (and
; release). Silent for now — the composed theme arrives in Unit 18. Words use the
; ROM's own 8x8 font at $3D00.
; ----------------------------------------------------------------------------
show_title:
di
call clear_screen
ld hl, str_title
ld b, 8
ld c, 11
call print_string
ld hl, str_prompt
ld b, 16
ld c, 6
call print_string
.tt_wait:
ld bc, KEYS_SPACE
in a, (c)
bit 0, a
jr nz, .tt_wait
.tt_rel:
ld bc, KEYS_SPACE
in a, (c)
bit 0, a
jr z, .tt_rel
ret
; show_win — the keep is cleared. Black screen, the words, the flourish, then
; wait for SPACE (and release) to return to the title.
show_win:
di
call clear_screen
ld hl, str_won
ld b, 9
ld c, 8
call print_string
ld hl, str_again
ld b, 15
ld c, 5
call print_string
call sfx_win
.sw_wait:
ld bc, KEYS_SPACE
in a, (c)
bit 0, a
jr nz, .sw_wait
.sw_rel:
ld bc, KEYS_SPACE
in a, (c)
bit 0, a
jr z, .sw_rel
ret
; win — the last coin is gone. Flourish, and raise the flag the loop watches.
win:
ld a, 1
ld (won), a
call sfx_win
ret
; sfx_win — an ascending flourish: a low note climbing in steps to a high one.
sfx_win:
ld c, 60
.swf_loop:
ld b, 12
push bc
call beep
pop bc
ld a, c
sub 8
ld c, a
cp 16
jr nc, .swf_loop
ret
; clear_screen — fill bitmap and attributes with zero: a black screen.
clear_screen:
ld hl, $4000
ld (hl), 0
ld de, $4001
ld bc, 6911
ldir
ret
; print_string — HL -> zero-terminated text, B = row, C = col.
print_string:
.ps_loop:
ld a, (hl)
or a
ret z
push hl
call print_char
pop hl
inc hl
inc c
jr .ps_loop
; print_char — A = character (32..127), B = row, C = col. Copies the ROM font
; glyph at $3D00 + (char-32)*8 to the screen, bright white.
print_char:
push bc
sub 32
ld l, a
ld h, 0
add hl, hl
add hl, hl
add hl, hl
ld de, $3D00
add hl, de
push hl
call scr_addr_cr
pop de
ld b, 8
.pc_row:
ld a, (de)
ld (hl), a
inc de
inc h
djnz .pc_row
pop bc
call attr_addr_cr
ld (hl), %01000111
ret
str_title:
defb "SHADOWKEEP", 0
str_prompt:
defb "PRESS SPACE TO ENTER", 0
str_won:
defb "THE KEEP STANDS", 0
str_again:
defb "PRESS SPACE TO RETURN", 0
; ----------------------------------------------------------------------------
; show_lose — the mirror of show_win. Black screen, the words, the freezing
; sting, then wait for SPACE (and release) to return to the title.
; ----------------------------------------------------------------------------
show_lose:
di
call clear_screen
ld hl, str_lost
ld b, 9
ld c, 8
call print_string
ld hl, str_again
ld b, 15
ld c, 5
call print_string
call sfx_caught
.slo_wait:
ld bc, KEYS_SPACE
in a, (c)
bit 0, a
jr nz, .slo_wait
.slo_rel:
ld bc, KEYS_SPACE
in a, (c)
bit 0, a
jr z, .slo_rel
ret
; sfx_caught — the plunge into stasis: a quick fall, then a deep, long toll as
; the stone closes over you. The opposite of the win flourish.
sfx_caught:
ld c, 16
.sca_fall:
ld b, 5
push bc
call beep
pop bc
ld a, c
add a, 7
ld c, a
cp 100
jr c, .sca_fall
ld b, 60
ld c, 130
call beep
ret
str_lost:
defb "THE KEEP SLEEPS", 0
scr_addr_cr:
ld a, b
and %00011000
or %01000000
ld h, a
ld a, b
and %00000111
rrca
rrca
rrca
or c
ld l, a
ret
attr_addr_cr:
ld a, b
ld l, a
ld h, 0
add hl, hl
add hl, hl
add hl, hl
add hl, hl
add hl, hl
ld de, $5800
add hl, de
ld a, c
ld e, a
ld d, 0
add hl, de
ret
palette:
defb '.'
defw floor_tile
defb FLOOR_ATTR
defb '#'
defw wall_tile
defb WALL_ATTR
defb '+'
defw mark_tile
defb MARK_ATTR
defb 'G'
defw gold_tile
defb GOLD_ATTR
defb 'T'
defw torch_tile
defb TORCH_ATTR
defb 'S'
defw statue_tile
defb STATUE_ATTR
defb 'B'
defw banner_tile
defb BANNER_ATTR
defb 'o'
defw rubble_tile
defb RUBBLE_ATTR
; ----------------------------------------------------------------------------
; The keep: three rooms. Hall -east-> Gallery -north-> Vault, and back.
; entry: map ptr, North, South, East, West
; ----------------------------------------------------------------------------
rooms:
defw room0_state
defb NO_EXIT, NO_EXIT, 1, NO_EXIT ; Hall: east -> Gallery
defw room1_state
defb 2, NO_EXIT, NO_EXIT, 0 ; Gallery: north -> Vault, west -> Hall
defw room2_state
defb NO_EXIT, 1, NO_EXIT, NO_EXIT ; Vault: south -> Gallery
; The Great Hall — four pillars, east door at row 11.
room0_template:
defb "###############T################"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "B..............S...............B"
defb "#.............ooo.........G....#"
defb "#..............................#"
defb "#........##..........##........#"
defb "#........##..........##........#"
defb "#..............................#"
defb "#..............................."
defb "#..............................#"
defb "#..............................#"
defb "#........##..........##........#"
defb "#........##..........##........#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#.........................G....#"
defb "#..............................#"
defb "#..............................#"
defb "################################"
; The Gallery — a dividing wall with one gap (column 15). West door (row 11)
; back to the Hall; north door (column 15) up to the Vault.
room1_template:
defb "###############.################"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "###############.################"
defb "#..............................#"
defb "#..............................#"
defb "........................G......#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "B..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#........................ooo...#"
defb "#..............................#"
defb "#.......................G......#"
defb "#..............................#"
defb "#..............................#"
defb "###############T################"
; The Vault — a great altar of stone in the middle, south door (column 15)
; down to the Gallery.
room2_template:
defb "################################"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#.............#T##.............#"
defb "#.............####.............#"
defb "#.............####.............#"
defb "#.............####.............#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#..............................#"
defb "#.........G.........G..........#"
defb "#..............................#"
defb "#..............................#"
defb "###############.################"
floor_tile:
defb %10101010
defb %01010101
defb %10101010
defb %01010101
defb %10101010
defb %01010101
defb %10101010
defb %01010101
wall_tile:
defb %00010001
defb %00000000
defb %01000100
defb %00000000
defb %00010001
defb %00000000
defb %01000100
defb %00000000
mark_tile:
defb %00000000
defb %00011000
defb %00011000
defb %01111110
defb %01111110
defb %00011000
defb %00011000
defb %00000000
thief:
defb %00011000
defb %00111100
defb %01111110
defb %01111110
defb %01111110
defb %01111110
defb %00111100
defb %00100100
current_room:
defb 0
thief_col:
defb START_COL
thief_row:
defb START_ROW
tcol:
defb 0
trow:
defb 0
map_ptr:
defw 0
tile_ptr:
defw 0
tile_attr:
defb 0
under_thief:
defb 0, 0, 0, 0, 0, 0, 0, 0, 0
gold_remaining:
defb TOTAL_GOLD
won:
defb 0
under_warden:
defb 0, 0, 0, 0, 0, 0, 0, 0, 0
warden_col:
defb WARDEN_COL0
warden_row:
defb WARDEN_ROW0
warden_dir:
defb -1
warden_axis:
defb AXIS_VERT
warden_timer:
defb WARDEN_GATHER
caught:
defb 0
torch_col:
defb NO_TORCH
torch_row:
defb NO_TORCH
room0_state:
defs 768
room1_state:
defs 768
room2_state:
defs 768
end start
Walk the keep end to end and feel the rooms change under you — the broad light of the Hall, the medium Gallery, and the tight, fearful pocket of the Vault where the thief steps from black into a ring of altar-light:
Try this: re-light a room
Change a room’s room_falloff and watch its character flip. Give the Hall a 0 and the welcoming chamber becomes a cramped, shadowed box. Give the Vault a 3 and the crypt floods with light and loses all its menace. You’re not redrawing anything — you’re tuning a feeling with a single digit.
Try this: a pitch-black room with one candle
Build a small room, no wall torches, a single T in a far corner, falloff 0. Almost the whole room is black; one corner glows. Drop a coin or a doorway just at the edge of the light, so the player has to step into the dark on faith to reach it. Darkness you have to enter is one of the oldest tricks in the genre.
Try this: contrast by neighbour
Put a bright room next to a dark one and a dark next to bright. Walking from the lit Hall into the black Vault feels darker than the Vault would on its own, because your eye arrives expecting light. Mood is relative — you compose the journey, not just the room.
When it’s wrong, see why
- Every room looks the same.
shade_for_cellisn’t readingroom_fallofffor the current room — check the index iscurrent_roomand the shift loop runs that many times. - A room is all black. Its falloff is low and its torch is far from the floor (or missing). With falloff 0 the light barely reaches; make sure there’s a flame where you want the pool.
- A room is flatly bright. Falloff is too high for the room’s size, so even the far corners clamp to the lightest shades. Lower it, or move the torch.
- The thief gets darker/lighter as he moves — flickering. Shade is baked per draw, not per frame; if it flickers, something is redrawing the room every frame. It should only redraw on entry.
- The pool is square, not round. Still the Chebyshev distance — fine and characterful. Sum the axes for a diamond, or their squares for a circle, if you want softer pools.
Before and after
You started with a keep where every room was lit alike and finished with three rooms that feel different — the Hall open and welcoming, the Vault a tight, fearful crypt — without adding a thing. The lighting engine is exactly Unit 13’s; the change is one falloff byte per room and the choice of where each flame sits. That’s composition: not more features but restraint, using the Spectrum’s two-colour cell and a dither ramp — the same limit that looked like a wall in Unit 1 — as the instrument. The keep stopped being uniformly lit and started having moods.
What you’ve learnt
- Mood is a parameter. One byte of falloff per room turns the same lighting engine into welcoming, neutral, or fearful — composition, not new code.
- Place the light with intent. Where the flame sits, and how fast it fades, decides where the eye goes. In the Vault the light is the altar; everything else is permission to be dark.
- The constraint is the vocabulary. Two colours a cell and a dither ramp — the same limit that defined Unit 1 — is enough to make a room feel like somewhere. Restraint, not richness.
- Atmosphere is relative. Rooms read against their neighbours; you compose the walk through the keep, not just each screen.
What’s next
Each room can now hold a mood — but they were composed one at a time. In Unit 16, “A Keep with Character,” we pull back and treat the whole keep as one composition: a room can hold more than one flame, each floor cell lit by its nearest, so the three chambers read as parts of a single place with a single atmosphere. It’s the unit that turns “rooms with lighting” into “a keep you believe in” — the close of the Mood and Light sub-arc.