create repository with functional basic implementation

This commit is contained in:
2026-04-24 07:13:59 +02:00
commit 7014692d71
24 changed files with 1265 additions and 0 deletions

9
src/consts/colors.asm Normal file
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pub const colors.black = 0b000_000_00
pub const colors.blue = 0b000_000_11
pub const colors.green = 0b000_111_00
pub const colors.gray = 0b010_011_10
pub const colors.red = 0b111_000_00
pub const colors.pink = 0b111_000_11
pub const colors.orange = 0b111_100_00
pub const colors.yellow = 0b111_110_00
pub const colors.white = 0b111_111_11

17
src/consts/game.asm Normal file
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pub const game.direction_up = 0
pub const game.direction_right = 1
pub const game.direction_down = 2
pub const game.direction_left = 3
pub const game.direction_still = 4
; 1_000_000_000 nano second = 0x0000_0000_3B9A_CA00
; pub const game.tick_duration_0 = 0xCA00
; pub const game.tick_duration_1 = 0x3B9A
; pub const game.tick_duration_2 = 0x0000
; pub const game.tick_duration_3 = 0x0000
; 0.5 second = 500_000_000 nano second = 0x0000_0000_1DCD_6500
pub const game.tick_duration_0 = 0x6500
pub const game.tick_duration_1 = 0x1DCD
pub const game.tick_duration_2 = 0x0000
pub const game.tick_duration_3 = 0x0000

12
src/consts/keyboard.asm Normal file
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pub const keyboard.mask_key = 0x00FF
pub const keyboard.mask_event = 0x0100
pub const keyboard.event_released = 0x0000
pub const keyboard.event_pressed = 0x0100
pub const keyboard.key_min = 1
pub const keyboard.key_up = 1
pub const keyboard.key_right = 2
pub const keyboard.key_down = 3
pub const keyboard.key_left = 4
pub const keyboard.key_max = 4

10
src/consts/map.asm Normal file
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; map size 16x12 (or 15x11 with margins)
pub const map.width = 15
pub const map.height = 11
pub const map.size = 165 ; 11*15
pub const map.max_x = 14
pub const map.max_y = 10
pub const map.tiles.empty = 0
pub const map.tiles.wall = 1
pub const map.tiles.coin = 2

16
src/consts/offsets.asm Normal file
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;const free_ram_start = 8000
pub const offsets.screen = 8000 ; screen size: 80x60 = 4800
pub const offsets.tick_duration_high = 12800
pub const offsets.tick_duration_low = 12804
pub const offsets.next_tick_high = 12808
pub const offsets.next_tick_low = 128012
; State:
; U8 x coord
; U8 y coord
; U8 direction
pub const offsets.state_robot = 12816
pub const offsets.state_ghost = 12819

8
src/consts/scene.asm Normal file
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; given:
; - 16x12 tiles map
; - 5x5 pixels tile
pub const scene.margin_top = 2
pub const scene.margin_bottom = 3
pub const scene.margin_left = 2
pub const scene.margin_right = 3

26
src/consts/screen.asm Normal file
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; Screen pixel mode (settings #0)
; 0: ASCII 8
; 1: ASCII 24
; 2: Pixel 8
; 3: Pixel 24
; While in mode #2 (Pixel 8)
; Screen memory offset (settings #1)
; Screen resolutions (settings #2)
; 0. 80x60
; 1. 160x120
; 2. 256x192
; 3. 320x240
; 4. 640x480
; 5. 800x600
; 6. 920x720
; 7. 1024x768
pub const screen.mode_index = 0
pub const screen.mode_value = 2
pub const screen.offset_index = 1
pub const screen.resolution_index = 2
pub const screen.resolution_value = 0
pub const screen.width = 80
pub const screen.height = 60

18
src/consts/sprites.asm Normal file
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pub const sprites.width = 5
pub const sprites.height = 5 ; unused as sprite are all square
pub const sprites.size = 25 ; height x width
pub const sprites.rotation_0 = 0
pub const sprites.rotation_90 = 1
pub const sprites.rotation_180 = 2
pub const sprites.rotation_270 = 3
pub const sprites.empty = 0
pub const sprites.unimplemented = 1
pub const sprites.wall_end = 2
pub const sprites.wall_straight = 3
pub const sprites.wall_corner = 4
pub const sprites.robot = 5
pub const sprites.ghost = 6
pub const sprites.coin = 7
pub const sprites.max = 7 ; for lookup table

299
src/lib/drawing.asm Normal file
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include ../consts/offsets
include ../consts/map
include ../consts/screen
include ../consts/scene
include ../consts/sprites
include sprite_rotation
; /* Draw the whole (fill the screen memory with the values of the sprites based on the map)
; Inputs:
; Outputs:
; Locals:
; r1: x map coord
; r2: y map coord
; r3: sprite rotation
; r4: sprite id
; r12: rotation (returned by `sprite and rotation`)
; r13: sprite (returned by `get_sprite_id_and_rotation`)
; */
pub drawing.draw_whole_map:
push r1
push r2
push r3
push r4
push r12
push r13
mov r1, 0
mov r2, 0
draw_whole_map_loop:
call sprite_rotation.get_sprite_id_and_rotation
mov r3, r12
mov r4, r13
call drawing.draw_sprite_at_map_coord
add r1, r1, 1
cmp r1, map.width
jne draw_whole_map_loop
mov r1, 0
add r2, r2, 1
cmp r2, map.height
jne draw_whole_map_loop
pop r13
pop r12
pop r4
pop r3
pop r2
pop r1
ret
; /* Return the top-left pixel address of the tile at the given map coordinates
; Inputs:
; r1: map x coord
; r2: map y coord
; Locals:
; r3: counter
; r4: offset per tile row (screen width * tile height)
; Ouputs:
; r13: the pixel address
; */
get_tile_address:
push r3
push r4
mov r3, 0
mov r4, 0
get_tile_address_offset_per_row_loop:
add r4, r4, screen.width
add r3, r3, 1
cmp r3, sprites.height
jne get_tile_address_offset_per_row_loop
mov r13, offsets.screen
mov r3, 0
get_tile_address_margin_top_loop:
cmp r3, scene.margin_top
je get_tile_address_margin_top_loop_end
add r13, r13, screen.width
add r3, r3, 1
jmp get_tile_address_margin_top_loop
get_tile_address_margin_top_loop_end:
mov r3, 0
get_tile_address_tile_row_loop:
cmp r3, r2
je get_tile_address_tile_row_loop_end
add r13, r13, r4
add r3, r3, 1
jmp get_tile_address_tile_row_loop
get_tile_address_tile_row_loop_end:
add r13, r13, scene.margin_left
mov r3, 0
get_tile_address_tile_column_loop:
cmp r3, r1
je get_tile_address_tile_column_loop_end
add r13, r13, sprites.width
add r3, r3, 1
jmp get_tile_address_tile_column_loop
get_tile_address_tile_column_loop_end:
pop r4
pop r3
ret
; /* Get address of given sprite id
; Inputs:
; r1: sprite id
; Outputs:
; r13: address
; Locals:
; r2: jump address
; */
get_sprite_address:
push r1
push r2
cmp r1, sprites.max
jbe get_sprite_address_jmp_table_init
mov r1, sprites.unimplemented
get_sprite_address_jmp_table_init:
lsl r2, r1, 3 ; 2*instruction_size = *8 = <<3
add r2, r2, get_sprite_address_jmp_table_start
jmp r2
get_sprite_address_jmp_table_start:
; sprite_empty
add r13, zr, sprite_empty
jmp get_sprite_address_return
; sprite_unimplemented:
add r13, zr, sprite_unimplemented
jmp get_sprite_address_return
; sprite_wall_end
add r13, zr, sprite_wall_end
jmp get_sprite_address_return
; sprite_wall_straight
add r13, zr, sprite_wall_straight
jmp get_sprite_address_return
; sprite_wall_corner
add r13, zr, sprite_wall_corner
jmp get_sprite_address_return
; sprite_robot
add r13, zr, sprite_robot
jmp get_sprite_address_return
; sprite_ghost
add r13, zr, sprite_ghost
jmp get_sprite_address_return
; sprite_coin:
add r13, zr, sprite_coin
;jmp get_sprite_address_return
get_sprite_address_return:
pop r2
pop r1
ret
; /* Draw given sprite on the screen at given map coordinates
; Inputs:
; r1: map x coord
; r2: map y coord
; r3: sprite rotation
; r4: sprite id
; Outputs:
; Locals:
; r1: screen address
; r2: sprite address
; r13: value returned by call to `get_tile_address` and `get_sprite_address`
; */
pub drawing.draw_sprite_at_map_coord:
push r1
push r2
push r3
push r4
push r13
call get_tile_address
mov r1, r13
push r1
mov r1, r4
call get_sprite_address
mov r2, r13
pop r1
call draw_sprite
pop r13
pop r4
pop r3
pop r2
pop r1
ret
; /* Draw given sprite (by address) at given screen position (by address) with given rotation
; Inputs:
; r1: screen address
; r2: sprite address
; r3: rotation
; Outputs:
; Locals:
; r1: current screen pixel address
; r4: x
; r5: y
; r6: current sprite pixel address
; r7: color
; r8: x increment
; r9: y increment
; */
draw_sprite:
push r1
push r2
push r3
push r4
push r5
push r6
push r7
push r8
push r9
mov r6, r2
; rotation
draw_sprite_cmp_rotation_0:
cmp r3, sprites.rotation_0
jne draw_sprite_cmp_rotation_90
mov r8, 1
mov r9, 0
jmp draw_sprite_loop_init
draw_sprite_cmp_rotation_90:
cmp r3, sprites.rotation_90
jne draw_sprite_cmp_rotation_180
add r6, r6, sprites.size
sub r6, r6, sprites.width
sub r8, zr, sprites.width
mov r9, sprites.size
add r9, r9, 1
jmp draw_sprite_loop_init
draw_sprite_cmp_rotation_180:
cmp r3, sprites.rotation_180
jne draw_sprite_cmp_rotation_270
add r6, r6, sprites.size
sub r6, r6, 1
sub r8, zr, 1
mov r9, 0
jmp draw_sprite_loop_init
draw_sprite_cmp_rotation_270:
add r6, r6, sprites.width
sub r6, r6, 1
mov r8, sprites.width
sub r9, zr, sprites.size
sub r9, r9, 1
draw_sprite_loop_init:
mov r4, 0
mov r5, 0
draw_sprite_loop:
load_8 r7, [r6]
store_8 [r1], r7
add r4, r4, 1
add r1, r1, 1
add r6, r6, r8
cmp r4, sprites.width
jne draw_sprite_loop
mov r4, 0
add r6, r6, r9
add r1, r1, screen.width
sub r1, r1, sprites.width
add r5, r5, 1
cmp r5, sprites.width
jne draw_sprite_loop
pop r9
pop r8
pop r7
pop r6
pop r5
pop r4
pop r3
pop r2
pop r1
ret

26
src/lib/game.asm Normal file
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; /* Return the tile address from the given map coordinate
; Inputs:
; r1: x map coordinate
; r2: y map coordinate
; Outputs:
; r13: tile address
; */
pub game.get_tile_address_from_map_coord:
push r1
push r2
add r13, r1, map
get_tile_address_from_map_coord_loop:
cmp r2, 0
je get_tile_address_from_map_coord_loop_end
add r13, r13, map.width
sub r2, r2, 1
jmp get_tile_address_from_map_coord_loop
get_tile_address_from_map_coord_loop_end:
pop r2
pop r1
ret

171
src/lib/sprite_rotation.asm Normal file
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include ../consts/offsets
include ../consts/map
include ../consts/sprites
; /* Return the sprite id and rotation for the given map coordinates
; Inputs:
; r1: x map coord
; r2: y map coord
; Outputs:
; r12: sprite rotation
; r13: sprite id
; Locals:
; r3: tile id
; r4: map offset
; r5: counter
; r6: left tile id
; r7: up tile id
; r8: right tile id
; r9: down tile id
; */
pub sprite_rotation.get_sprite_id_and_rotation:
push r1
push r2
push r3
push r4
push r5
push r6
push r7
push r8
push r9
add r4, r1, map
mov r5, 0
get_sprite_id_and_rotation_map_row_loop:
cmp r5, r2
je get_sprite_id_and_rotation_map_row_loop_end
add r4, r4, map.width
add r5, r5, 1
jmp get_sprite_id_and_rotation_map_row_loop
get_sprite_id_and_rotation_map_row_loop_end:
mov r12, sprites.rotation_0 ; default rotation
load_8 r3, [r4]
lsl r3, r3, 3 ; 2*instruction_size = *8 = <<3
add r3, r3, get_sprite_id_and_rotation_jump_table
jmp r3
get_sprite_id_and_rotation_jump_table:
; tile_empty
mov r13, sprites.empty
jmp get_sprite_id_and_rotation_return
; tiles_wall
jmp get_sprite_id_and_rotation_wall
nop
; tile_coin
mov r13, sprites.coin
jmp get_sprite_id_and_rotation_return
get_sprite_id_and_rotation_wall:
mov r6, 0
mov r7, 0
mov r8, 0
mov r9, 0
get_sprite_id_and_rotation_cmp_left:
cmp r1, 0
je get_sprite_id_and_rotation_cmp_up
sub r4, r4, 1
load_8 r6, [r4]
add r4, r4, 1
get_sprite_id_and_rotation_cmp_up:
cmp r2, 0
je get_sprite_id_and_rotation_cmp_right
sub r4, r4, map.width
load_8 r7, [r4]
add r4, r4, map.width
get_sprite_id_and_rotation_cmp_right:
cmp r1, map.max_x
je get_sprite_id_and_rotation_cmp_down
add r4, r4, 1
load_8 r8, [r4]
sub r4, r4, 1
get_sprite_id_and_rotation_cmp_down:
cmp r2, map.max_y
je get_sprite_id_and_rotation_check_connections
add r4, r4, map.width
load_8 r9, [r4]
sub r4, r4, map.width
get_sprite_id_and_rotation_check_connections:
get_sprite_id_and_rotation_straight_0:
cmp r7, map.tiles.wall
jne get_sprite_id_and_rotation_straight_90
cmp r9, map.tiles.wall
jne get_sprite_id_and_rotation_straight_90
mov r12, sprites.rotation_0
mov r13, sprites.wall_straight
jmp get_sprite_id_and_rotation_return
get_sprite_id_and_rotation_straight_90:
cmp r6, map.tiles.wall
jne get_sprite_id_and_rotation_corner_0
cmp r8, map.tiles.wall
jne get_sprite_id_and_rotation_corner_0
mov r12, sprites.rotation_90
mov r13, sprites.wall_straight
jmp get_sprite_id_and_rotation_return
get_sprite_id_and_rotation_corner_0:
cmp r6, map.tiles.wall
jne get_sprite_id_and_rotation_corner_180
cmp r9, map.tiles.wall
jne get_sprite_id_and_rotation_corner_90
mov r12,sprites.rotation_0
mov r13, sprites.wall_corner
jmp get_sprite_id_and_rotation_return
get_sprite_id_and_rotation_corner_90:
cmp r7, map.tiles.wall
jne get_sprite_id_and_rotation_end_90
mov r12,sprites.rotation_90
mov r13, sprites.wall_corner
jmp get_sprite_id_and_rotation_return
get_sprite_id_and_rotation_corner_180:
cmp r8, map.tiles.wall
jne get_sprite_id_and_rotation_end_0
cmp r7, map.tiles.wall
jne get_sprite_id_and_rotation_corner_270
mov r12,sprites.rotation_180
mov r13, sprites.wall_corner
jmp get_sprite_id_and_rotation_return
get_sprite_id_and_rotation_corner_270:
cmp r9, map.tiles.wall
jne get_sprite_id_and_rotation_end_270
mov r12,sprites.rotation_270
mov r13, sprites.wall_corner
jmp get_sprite_id_and_rotation_return
get_sprite_id_and_rotation_end_0:
cmp r9, map.tiles.wall
jne get_sprite_id_and_rotation_end_180
mov r12,sprites.rotation_0
mov r13, sprites.wall_end
jmp get_sprite_id_and_rotation_return
get_sprite_id_and_rotation_end_90:
mov r12,sprites.rotation_90
mov r13, sprites.wall_end
jmp get_sprite_id_and_rotation_return
get_sprite_id_and_rotation_end_180:
mov r12,sprites.rotation_180
mov r13, sprites.wall_end
jmp get_sprite_id_and_rotation_return
get_sprite_id_and_rotation_end_270:
mov r12,sprites.rotation_270
mov r13, sprites.wall_end
;jmp get_sprite_id_and_rotation_return
get_sprite_id_and_rotation_return:
pop r9
pop r8
pop r7
pop r6
pop r5
pop r4
pop r3
pop r2
pop r1
ret

369
src/main.asm Normal file
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include consts/screen
;
; Screen initialization
;
; r1 = screen parameter value
mov r1, screen.mode_index
screen r1, screen.mode_value
mov r1, screen.offset_index
screen r1, offsets.screen
mov r1, screen.resolution_index
screen r1, screen.resolution_value
call drawing.draw_whole_map
;
; State initialization
;
; Robot
const robot_initial_x = 1
const robot_initial_y = 1
const robot_initial_direction = game.direction_down
mov r1, robot_initial_x
mov r2, robot_initial_y
mov r5, robot_initial_direction
mov r6, offsets.state_robot
store_8 [r6], r1
add r6, r6, 1
store_8 [r6], r2
add r6, r6, 1
store_8 [r6], r5
mov r3, sprites.rotation_0
mov r4, sprites.robot
call drawing.draw_sprite_at_map_coord
; Ghost
const ghost_initial_x = 13
const ghost_initial_y = 1
const ghost_initial_direction = game.direction_down
mov r1, ghost_initial_x
mov r2, ghost_initial_y
mov r5, ghost_initial_direction
mov r6, offsets.state_ghost
store_8 [r6], r1
add r6, r6, 1
store_8 [r6], r2
add r6, r6, 1
store_8 [r6], r5
mov r3, sprites.rotation_0
mov r4, sprites.ghost
call drawing.draw_sprite_at_map_coord
;
; Time initialization
;
mov r2, game.tick_duration_1
movt r2, r2
movb r2, game.tick_duration_0
mov r1, offsets.tick_duration_low
store_32 [r1], r2
mov r3, game.tick_duration_3
movt r3, r3
movb r3, game.tick_duration_2
mov r1, offsets.tick_duration_high
store_32 [r1], r3
time_0 r4
time_1 r5
add r4, r4, r2
add r5, r5, r3
cmp r4, r2
jae init_store_next_tick
add r5, r5, 1 ; overflow
init_store_next_tick:
mov r1, offsets.next_tick_low
store_32 [r1], r4
mov r1, offsets.next_tick_high
store_32 [r1], r5
game_loop:
;
; Event handling
;
; r1 = keyboard event+key / direction
; r2 = keyboard key / direction address
; r3 = keyboard event
; r4 = jump address
keyboard r1
and r2, r1, keyboard.mask_key
and r3, r1, keyboard.mask_event
cmp r3, keyboard.event_pressed
jne game_loop_event_handling_end
cmp r2, keyboard.key_min
jb game_loop_event_handling_end
cmp r2, keyboard.key_max
ja game_loop_event_handling_end
sub r4, r2, keyboard.key_min ; so the first value is 0
lsl r4, r4, 3 ; 2 * instruction length = 8
add r4, r4, game_loop_key_jump_table_start
jmp r4
game_loop_key_jump_table_start:
; key_up
mov r1, game.direction_up
jmp game_loop_event_handling_store_direction
; key_right
mov r1, game.direction_right
jmp game_loop_event_handling_store_direction
; key_down:
mov r1, game.direction_down
jmp game_loop_event_handling_store_direction
; key_left:
mov r1, game.direction_left
; jmp game_loop_event_handling_end
game_loop_event_handling_store_direction:
add r2, zr, offsets.state_robot
add r2, r2, 2
store_8 [r2], r1
game_loop_event_handling_end:
;
; Elapsed time check
;
; r1: address
; r2: now low / delay low
; r3: now high / delay high
; r4: next tick low
; r5: next tick high
;
time_0 r2
time_1 r3
mov r1, offsets.next_tick_low
load_32 r4, [r1]
mov r1, offsets.next_tick_high
load_32 r5, [r1]
cmp r3, r5
jb game_loop
ja update_next_tick
cmp r2, r4
jb game_loop
update_next_tick:
mov r1, offsets.tick_duration_low
load_32 r2, [r1]
mov r1, offsets.tick_duration_high
load_32 r3, [r1]
add r4, r4, r2
add r5, r5, r3
cmp r4, r2
jae store_next_tick
add r5, r5, 1
store_next_tick:
mov r1, offsets.next_tick_low
store_32 [r1], r4
mov r1, offsets.next_tick_high
store_32 [r1], r5
;
; Robot movement
;
; r1 = robot's state address
; r2 = x
; r3 = y
; r4 = direction
; r5 = new x
; r6 = new y
; r7 = new position address
; r8 = new position content
; r9 = jump address
mov r1, offsets.state_robot
load_8 r2, [r1]
add r1, r1, 1
load_8 r3, [r1]
add r1, r1, 1
load_8 r4, [r1]
mov r5, r2
mov r6, r3
lsl r9, r4, 3 ; 2 * instruction size = 8
add r9, r9, game_loop_robot_movement_jump_table_start
jmp r9
game_loop_robot_movement_jump_table_start:
; direction_up
sub r6, r6, 1
jmp game_loop_robot_movement_try_move
; direction_right
add r5, r5, 1
jmp game_loop_robot_movement_try_move
; direction_down
add r6, r6, 1
jmp game_loop_robot_movement_try_move
; direction_left
sub r5, r5, 1
jmp game_loop_robot_movement_try_move
; direction_still
jmp game_loop_robot_movement_none
game_loop_robot_movement_try_move:
push r2
mov r1, r5
mov r2, r6
call game.get_tile_address_from_map_coord
mov r7, r13
pop r2
;
; Collision handling
;
load_8 r8, [r7]
cmp r8, map.tiles.wall
jne game_loop_robot_movement_some
; hit wall
mov r1, offsets.state_robot
add r1, r1, 2
mov r4, game.direction_still
store_8 [r1], r4
jmp game_loop_robot_movement_none
game_loop_robot_movement_some:
; TODO: handle coin and empty differently
mov r8, map.tiles.empty
store_8 [r7], r8
mov r1, offsets.state_robot
store_8 [r1], r5
add r1, r1, 1
store_8 [r1], r6
; clear old position
mov r1, r2
mov r2, r3
mov r3, sprites.rotation_0
mov r4, sprites.empty
call drawing.draw_sprite_at_map_coord
; draw robot on new position
mov r1, r5
mov r2, r6
mov r3, sprites.rotation_0
mov r4, sprites.robot
call drawing.draw_sprite_at_map_coord
game_loop_robot_movement_none:
;
; Ghost movement
;
; r1: ghost's state address
; r2: x
; r3: y
; r4: direction
; r5: x increment
; r6: y increment
; r7: new x
; r8: new y
; r9: new position address
; r10: new position content
; r11: jump address
mov r1, offsets.state_ghost
load_8 r2, [r1]
add r1, r1, 1
load_8 r3, [r1]
add r1, r1, 1
load_8 r4, [r1]
mov r5, 0
mov r6, 0
lsl r11, r4, 3 ; 2 * instruction size = 8
add r11, r11, game_loop_ghost_movement_jump_table_start
jmp r11
game_loop_ghost_movement_jump_table_start:
; direction_up
sub r6, r6, 1
jmp game_loop_ghost_movement_make_move
; direction_right
add r5, r5, 1
jmp game_loop_ghost_movement_make_move
; direction_down
add r6, r6, 1
jmp game_loop_ghost_movement_make_move
; direction_left
sub r5, r5, 1
;jmp game_loop_ghost_movement_make_move
; direction_still (should never happen)
game_loop_ghost_movement_make_move:
add r7, r2, r5
add r8, r3, r6
mov r1, offsets.state_ghost
store_8 [r1], r7
add r1, r1, 1
store_8 [r1], r8
; get tile at previous position
push r2
mov r1, r2
mov r2, r3
call game.get_tile_address_from_map_coord
mov r9, r13
pop r2
; draw tile at previous position
load_8 r1, [r9]
cmp r1, map.tiles.coin
je game_loop_ghost_movement_old_tile_coin
; old tile empty
mov r4, sprites.empty
jmp game_loop_ghost_movement_draw_old_tile
game_loop_ghost_movement_old_tile_coin:
mov r4, sprites.coin
game_loop_ghost_movement_draw_old_tile:
mov r1, r2
mov r2, r3
mov r3, sprites.rotation_0
call drawing.draw_sprite_at_map_coord
; draw ghost on new position
mov r1, r7
mov r2, r8
mov r3, sprites.rotation_0
mov r4, sprites.ghost
call drawing.draw_sprite_at_map_coord
;
; Check ahead for direction change
;
add r1, r7, r5
add r2, r8, r6
call game.get_tile_address_from_map_coord
load_8 r10, [r13]
cmp r10, map.tiles.wall
jne game_loop_ghost_movement_end
; increment direction
mov r1, offsets.state_ghost
add r1, r1, 2
load_8 r4, [r1]
add r4, r4, 1
and r4, r4, 0b11 ; modulo 3
store_8 [r1], r4
game_loop_ghost_movement_end:
jmp game_loop
include lib/drawing