diff --git a/png/map/intro_coll.png b/png/map/intro_coll.png
index 6fac243..fdb70c8 100644
Binary files a/png/map/intro_coll.png and b/png/map/intro_coll.png differ
diff --git a/scripts/generate_map.py b/scripts/generate_map.py
index 29f8799..94f0b6f 100644
--- a/scripts/generate_map.py
+++ b/scripts/generate_map.py
@@ -16,7 +16,9 @@ def abort(msg: str) -> NoReturn:
     sys.exit(1)
 
 
-def generate_coll_map(in_path: pathlib.Path, width: int, height: int) -> str:
+def generate_coll_map(
+    in_path: pathlib.Path, width: int, height: int, compress: bool = False
+) -> str:
     png = Image.open(in_path).convert("RGB")
     if png.width % 8 != 0 or png.height % 8 != 0:
         abort(f"file '{in_path}' has invalid dimensions (should be multiple of 8)")
@@ -33,37 +35,35 @@ def generate_coll_map(in_path: pathlib.Path, width: int, height: int) -> str:
 
             bit = None
             if pixel == RED:
-                bit = 1
-            elif pixel == GREEN:
                 bit = 0
+            elif pixel == GREEN:
+                bit = 1
             else:
                 abort(f"unsupported pixel in collision map: {pixel}")
 
-            bits.append(bit)
-            if len(bits) == 8:
-                byte = sum([bit << i for i, bit in enumerate(bits)])
-                out_bytes.append(byte)
-                bits = []
+            if compress:
+                bits.append(bit)
+                if len(bits) == 8:
+                    byte = sum([bit << i for i, bit in enumerate(bits)])
+                    out_bytes.append(byte)
+                    bits = []
+            else:
+                out_bytes.append(bit)
 
     png.close()
-
-    lines = []
-    for line_no in range(0, len(out_bytes), 16):
-        line = out_bytes[line_no : line_no + 16]
-        lines.append("    DB " + ", ".join(["$%02X" % b for b in line]))
-
-    return "\n".join(lines)
+    return format_bytes(out_bytes, width=width)
 
 
-def format_bytes(data: bytes) -> str:
+def format_bytes(data: bytes, width: int = 16) -> str:
+    print(f"formatting with width={width}")
     lines = []
-    for line_no in range(0, len(data), 16):
-        line = data[line_no : line_no + 16]
+    for line_no in range(0, len(data), width):
+        line = data[line_no : line_no + width]
         lines.append("    DB " + ", ".join(["$%02X" % b for b in line]))
     return "\n".join(lines)
 
 
-def generate_map(pngfile: str) -> None:
+def generate_map(pngfile: str, compress: bool = False) -> None:
     pngpath = pathlib.Path(pngfile).resolve()
     incpath = pngpath.parent / pngpath.name.replace(".png", ".inc")
     spath = pngpath.parent / pngpath.name.replace(".png", ".s")
@@ -90,13 +90,13 @@ def generate_map(pngfile: str) -> None:
             ]
         )
 
-        map_data = format_bytes(tilef.read())
+        map_data = format_bytes(tilef.read(), width=width)
         tile_data = format_bytes(mapf.read())
 
     section = pngpath.name.replace(".png", "")
 
     collpath = pngpath.parent / pngpath.name.replace(".png", "_coll.png")
-    coll_map = generate_coll_map(collpath, width, height)
+    coll_map = generate_coll_map(collpath, width, height, compress=compress)
 
     with open(incpath, "w") as outf:
         outf.write(
@@ -131,9 +131,10 @@ ASSERT {section}_MAP_SIZE == {section}_WIDTH * {section}_HEIGHT
 
 def main() -> None:
     parser = argparse.ArgumentParser("generate_map")
+    parser.add_argument("-c", "--compress", default=False)
     parser.add_argument("png")
     args = parser.parse_args()
-    generate_map(args.png)
+    generate_map(args.png, compress=(not not args.compress))
 
 
 if __name__ == "__main__":
diff --git a/src/bg.s b/src/bg.s
index 7ee1323..0a4d878 100644
--- a/src/bg.s
+++ b/src/bg.s
@@ -1,7 +1,23 @@
 INCLUDE "hardware.inc"
 INCLUDE "png/map/intro.inc"
 
-SECTION "BG0", ROM0
+SECTION "BG Data", WRAM0
+
+BG_COLLISION_DATA:: dw
+BG_MAP_WIDTH:: db
+
+SECTION "BG Code", ROM0
+
+MACRO update_map_info
+    ld hl, BG_COLLISION_DATA
+    ld a, HIGH(\1)
+    ld [hli], a
+    ld a, LOW(\1)
+    ld [hli], a
+
+    ld a, \2
+    ld [hli], a
+ENDM
 
 BG_Init::
     ; copy map
@@ -31,4 +47,6 @@ BG_Init::
     ld d, intro_NUM_TILES
     call memcpy
 
+    update_map_info intro_COLLISION, intro_WIDTH
+
     ret
diff --git a/src/collision.s b/src/collision.s
new file mode 100644
index 0000000..9057ddf
--- /dev/null
+++ b/src/collision.s
@@ -0,0 +1,133 @@
+INCLUDE "oam.inc"
+
+SECTION "Collision", ROMX
+
+; Check whether a 16x16 metasprite collides with the background
+; @param a The index of the first (top left) OAM entry of the sprite
+; @destroy hl
+; note: doesn't work atm (use srl, not sra?)
+sprite16x16_bg_collides::
+    ; compute oam entry address (_OAM + a * 4)
+    ; a is guaranteed not to overflow since l = $00 and a < 40
+    ld hl, _OAM
+    sla a
+    sla a
+    add l
+    ld l, a
+
+    ; top left (x,y)
+    ld a, [hl+]
+    sra a
+    sra a
+    sra a
+    ld c, [hl]
+    sra c
+    sra c
+    sra c
+    call can_move_to
+    ret nz
+
+    ; other three sprites
+    REPT 3
+        ld a, [hl+]
+        sra a
+        sra a
+        sra a
+        ld c, [hl]
+        sra c
+        sra c
+        sra c
+        call can_move_to
+        ret nz
+    ENDR
+
+    ret
+
+player_bg_collides::
+    ; c = x/8
+    ld hl, PLAYER_X
+    ld a, [hl]
+    ld c, a
+    and %111
+    jr z, .skip_inc_c
+    ld a, c
+    add 8
+    ld c, a
+.skip_inc_c:
+    srl c
+    srl c
+    srl c
+
+    ; b = y/8
+    inc hl
+    ld a, [hl]
+    ld b, a
+    and %111
+    jr z, .skip_inc_b
+    ld a, b
+    add 8
+    ld b, a
+.skip_inc_b:
+    srl b
+    srl b
+    srl b
+
+    ; top left
+    call can_move_to
+    ret z
+
+    ; top right
+    inc c
+    call can_move_to
+    ret z
+
+    ; bottom left
+    dec c
+    inc b
+    call can_move_to
+    ret z
+
+    ; bottom right
+    inc c
+    call can_move_to
+
+    ret
+
+; Check whether the location can be moved to or not
+; @param b y-coordinate
+; @param c x-coordinate
+; @destroy a, d, e
+; @note Z = false, NZ = true
+can_move_to:
+    ; todo: should be aware of scx/scy
+    push bc
+    push hl
+
+    ; hl = bg_collision_data
+    ld hl, BG_COLLISION_DATA
+    ld d, [hl]
+    inc hl
+    ld e, [hl]
+    push de
+
+    ; de = map width
+    ld hl, BG_MAP_WIDTH
+    ld d, 0
+    ld e, [hl]
+    pop hl
+
+    ; compute map index (HL + B * (BG_MAP_WIDTH + 1) + C)
+.mul_y_width:
+    add hl, de
+    dec b
+    jr nz, .mul_y_width
+    add hl, bc
+
+    ; check [hl] = 1
+    ld a, [hl]
+    cp 0
+
+    pop hl
+    pop bc
+
+    ret
diff --git a/src/player.s b/src/player.s
index b8d3578..1aafa71 100644
--- a/src/player.s
+++ b/src/player.s
@@ -7,6 +7,11 @@ Section "Player Data", WRAM0
 playerWorldX: dw
 playerWorldY: dw
 
+; player data
+PLAYER_X:: db
+PLAYER_Y:: db
+PLAYER_DIR:: db
+
 Section "Player Code", ROM0
 
 spriteData:
@@ -18,6 +23,14 @@ DEF SPRITE_WIDTH EQU 2
 DEF SPRITE_HEIGHT EQU 2
 
 Player_Init::
+    ; clear player data
+    ld hl, PLAYER_X
+    ld [hl], 0
+    inc hl
+    ld [hl], 144-32
+    inc hl
+    ld [hl], 0
+
     ld a, 8
     ld hl, _OAM + 1
     ld [hl], a
@@ -56,13 +69,27 @@ Player_Update::
     jr z, .left
 
     ; check for right boundary
-    ld_OAM_x hl, SPRITE_OAM_IDX + 1
+    ld hl, PLAYER_X
     ld a, [hl]
+    add 16
     cp SCRN_X
     jr nc, .left
 
-    ; TODO: check collision
-    call move_right
+    inc [hl]
+
+    call player_bg_collides
+    jr z, .right_rollback
+
+    ld hl, PLAYER_DIR
+    ld [hl], 0
+
+    call update_oam
+    ret
+
+.right_rollback:
+    ld hl, PLAYER_X
+    dec [hl]
+    ret
 
 .left:
     ; check for left button
@@ -71,90 +98,97 @@ Player_Update::
     ret z
 
     ; check for left boundary
-    ld_OAM_x hl, SPRITE_OAM_IDX
+    ld hl, PLAYER_X
     ld a, [hl]
-    cp 9
-    ret c
+    or a
+    ret z
 
-    ; TODO: check collision
-    call move_left
+    dec [hl]
 
-    ret
+    call player_bg_collides
+    jr z, .left_rollback
 
-move_right:
-    ld_OAM_x hl, SPRITE_OAM_IDX
+    ld hl, PLAYER_DIR
+    ld [hl], $ff
 
-    ; update top left sprite
-    inc [hl]
-    inc hl
-    ld [hl], SPRITE_IDX
-    inc hl
-    res OAMB_XFLIP, [hl]
+    call update_oam
+    ret
 
-    ; update top right sprite
-    inc hl
-    inc hl
-    inc [hl]
-    inc hl
-    ld [hl], SPRITE_IDX + 1
-    inc hl
-    res OAMB_XFLIP, [hl]
+.left_rollback:
+    ld hl, PLAYER_X
+    dec [hl]
+    ret
 
-    ; update bottom left sprite
-    inc hl
-    inc hl
-    inc [hl]
-    inc hl
-    ld [hl], SPRITE_IDX + 2
-    inc hl
-    res OAMB_XFLIP, [hl]
+; Update sprite OAM entries with current position and direction
+update_oam:
+    ld hl, PLAYER_DIR
+    ld a, [hl-] ; dir (0 = right , $ff = left)
+    and OAMF_XFLIP
+    ld c, a
 
-    ; update bottom right sprite
-    inc hl
-    inc hl
-    inc [hl]
-    inc hl
-    ld [hl], SPRITE_IDX + 3
-    inc hl
-    res OAMB_XFLIP, [hl]
+    ld a, [hl-] ; y
+    add 16
 
-    ret
+    ld d, a
+    ld a, [hl] ; x
+    add 8
+    ld b, a
+    ld a, d
 
-move_left:
-    ld_OAM_x hl, SPRITE_OAM_IDX
+    ld_OAM_y hl, SPRITE_OAM_IDX
 
-    ; top left
-    dec [hl]
+    ; top left sprite
+    ld [hli], a
+    ld [hl], b
     inc hl
-    ld [hl], SPRITE_IDX + 1
+    ld [hl], SPRITE_IDX
+    inc hl
+    ld [hl], c
     inc hl
-    set OAMB_XFLIP, [hl]
 
     ; top right
+    ld d, a
+    ld a, b
+    add 8
+    ld b, a
+    ld a, d
+
+    ld [hli], a
+    ld [hl], b
     inc hl
+    ld [hl], SPRITE_IDX + 1
     inc hl
-    dec [hl]
-    inc hl
-    ld [hl], SPRITE_IDX
+    ld [hl], c
     inc hl
-    set OAMB_XFLIP, [hl]
 
     ; bottom left
+    add 8
+    ld d, a
+    ld a, b
+    sub 8
+    ld b, a
+    ld a, d
+
+    ld [hli], a
+    ld [hl], b
     inc hl
+    ld [hl], SPRITE_IDX + 2
     inc hl
-    dec [hl]
-    inc hl
-    ld [hl], SPRITE_IDX + 3
+    ld [hl], c
     inc hl
-    set OAMB_XFLIP, [hl]
 
     ; bottom right
+    ld d, a
+    ld a, b
+    add 8
+    ld b, a
+    ld a, d
+
+    ld [hli], a
+    ld [hl], b
     inc hl
+    ld [hl], SPRITE_IDX + 3
     inc hl
-    dec [hl]
-    inc hl
-    ld [hl], SPRITE_IDX + 2
-    inc hl
-    set OAMB_XFLIP, [hl]
+    ld [hl], c
 
     ret