Add `get_tilemap` and `get_unused_overlay`

draw_tile.asm

@@ -9,6 +9,8 @@ const TILEMAP_HEIGHT: 0x01FFFFF8
 ; r0: pointer to tilemap data
 ; r1: tile width
 ; r2: tile height
+; outputs:
+; none
 set_tilemap:
     mov [TILEMAP_POINTER], r0
     mov [TILEMAP_WIDTH], r1
@@ -16,6 +18,20 @@ set_tilemap:
 
     ret
 
+; get the current tilemap
+; inputs:
+; none
+; outputs:
+; r0: pointer to tilemap data
+; r1: tile width
+; r2: tile height
+get_tilemap:
+    mov r0, [TILEMAP_POINTER]
+    mov r1, [TILEMAP_WIDTH]
+    mov r2, [TILEMAP_HEIGHT]
+
+    ret
+
 ; draw a single tile to a framebuffer
 ; inputs:
 ; r0: tile number

fox32rom.def

@@ -19,6 +19,7 @@ draw_tile_generic:                        jmp [0xF0041014]
 set_tilemap:                              jmp [0xF0041018]
 draw_pixel_generic:                       jmp [0xF004101C]
 draw_filled_rectangle_generic:            jmp [0xF0041020]
+get_tilemap:                              jmp [0xF0041024]
 
 ; background jump table
 fill_background:                          jmp [0xF0042000]
@@ -48,6 +49,7 @@ disable_overlay:                          jmp [0xF0043030]
 move_overlay:                             jmp [0xF0043034]
 resize_overlay:                           jmp [0xF0043038]
 set_overlay_framebuffer_pointer:          jmp [0xF004303C]
+get_unused_overlay:                       jmp [0xF0043040]
 
 ; menu bar jump table
 enable_menu_bar:                          jmp [0xF0044000]

main.asm

@@ -189,6 +189,7 @@ get_rom_version:
     data.32 set_tilemap
     data.32 draw_pixel_generic
     data.32 draw_filled_rectangle_generic
+    data.32 get_tilemap
 
     ; background jump table
     org.pad 0xF0042000
@@ -220,6 +221,7 @@ get_rom_version:
     data.32 move_overlay
     data.32 resize_overlay
     data.32 set_overlay_framebuffer_pointer
+    data.32 get_unused_overlay
 
     ; menu bar jump table
     org.pad 0xF0044000

overlay.asm

@@ -505,3 +505,32 @@ make_coordinates_relative_to_overlay:
     pop r3
     pop r2
     ret
+
+; find the first disabled overlay, starting from 0
+; inputs:
+; none
+; outputs:
+; r0: overlay number, or 0xFF if all overlays are enabled
+get_unused_overlay:
+    push r1
+    push r31
+
+    mov r0, 0x80000000
+    mov r31, 31
+get_unused_overlay_loop:
+    in r1, r0
+    cmp r1, 0
+    ifz jmp get_unused_overlay_found
+    inc r0
+    loop get_unused_overlay_loop
+    mov r0, 0xFF
+
+    pop r31
+    pop r1
+    ret
+get_unused_overlay_found:
+    and r0, 0x000000FF
+
+    pop r31
+    pop r1
+    ret