Routines
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6D17: Level overview screen
Displays a preview fly-over of the upcoming terrain before the game starts. Shows scrolling terrain with game number and scrolling title text. Player can press Enter to start the game early, or wait for 5 scroll units to auto-start.
  • Initializes screen with PAPER RIVER, INK BANK
  • Prints status line and "GAME n" where n is the game mode (1-4)
  • Runs a main loop that scrolls terrain and displays title text
  • Exits to game start after 5 scroll increments or Enter key
overview 6D17 LD BC,$0010 Initialize scroll position (state_scroll_offset = $0010) and scroll speed (state_island_line_idx = $10).
6D1A LD ($5F70),BC
6D1E LD A,$10
6D20 LD ($5EFD),A
6D23 LD D,$0C Set screen colors (PAPER RIVER, INK BANK) via clear_screen.
6D25 CALL clear_screen
6D28 CALL init_udg Clear/initialize screen via init_udg.
6D2B LD DE,$8000 Print status line 1 (status_line_1, length $31 bytes) using ROM PR_STRING ($203C).
6D2E LD BC,$0031
6D31 CALL $203C
6D34 CALL print_bridge Initialize gameplay: call print_bridge, setup_overview_status_player_2, init_starting_bridge (init_starting_bridge).
6D37 CALL setup_overview_status_player_2
6D3A CALL init_starting_bridge
6D3D CALL init_current_bridge Initialize terrain rendering.
6D40 LD A,$04 Print "GAME" text (status_line_4, length 5) using ROM PR_STRING.
6D42 LD ($5EEE),A
6D45 LD DE,$805A
6D48 LD BC,$0005
6D4B CALL $203C
6D4E LD A,($923A) Print game number: load game mode from state_game_mode, add "1" for ASCII digit, output via RST $10.
6D51 ADD A,$31
6D53 RST $10
6D54 LD A,$68 Initialize state: set LAST_K to 'h' (paused state), clear state_terrain_position, save initial scroll value to state_overview_start_scroll.
6D56 LD ($5C08),A
6D59 LD A,$00
6D5B LD ($5F7D),A
6D5E LD A,($5EF0)
6D61 LD ($5D43),A
This entry point is used by the routine at reset_scroll_text.
overview_loop 6D64 LD A,$BF Check Enter key (row 6, bit 0). Handle Enter if pressed.
6D66 IN A,($FE)
6D68 BIT 0,A
6D6A CALL Z,handle_enter
6D6D LD A,($5D43) Check if 5 scroll units passed: if (state_bridge_index - state_overview_start_scroll) == 5, jump to return_to_control_selection to start game.
6D70 LD B,A
6D71 LD A,($5EF0)
6D74 SUB B
6D75 CP $05
6D77 JP Z,return_to_control_selection
6D7A CALL scroll_text_crawl Text crawl: 1st of 2 pixel shifts this frame.
6D7D CALL render_plane_and_terrain Render plane and terrain, increment tick counter, operate viewport objects and projectiles.
6D80 LD HL,$5EEF
6D83 INC (HL)
6D84 CALL operate_viewport_slots
6D87 CALL operate_tank_shell
6D8A CALL operate_helicopter_missile
6D8D CALL advance_scroll Advance terrain scroll and render terrain.
6D90 CALL scroll_text_crawl Text crawl: 2nd of 2 pixel shifts this frame.
6D93 LD HL,$5F81 Increment frame counter state_overview_frame, scan keyboard, enable interrupts.
6D96 INC (HL)
6D97 CALL $02BF
6D9A EI
6D9B LD A,($5C08) Check if Enter was pressed. If so, jump to play.
6D9E CP $0D
6DA0 JP Z,play
6DA3 LD A,($5F81) Check frame counter AND 3: if not zero, loop back to overview_loop.
6DA6 AND $03
6DA8 CP $00
6DAA JP NZ,overview_loop
6DAD LD A,$01 Open lower screen (K) channel via ROM CHAN_OPEN ($1601) to print next text crawl character.
6DAF CALL $1601
6DB2 LD A,$10 INK BLACK
6DB4 RST $10
6DB5 LD A,$00
6DB7 RST $10
6DB8 LD A,$11 PAPER BLACK
6DBA RST $10
6DBB LD A,$00
6DBD RST $10
6DBE LD A,$16 AT 1,31 — bottom-right corner of the lower screen (char row 23, column 31).
6DC0 RST $10
6DC1 LD A,$01
6DC3 RST $10
6DC4 LD A,$1F
6DC6 RST $10
6DC7 LD HL,($5F7E) Advance text pointer (ptr_scroller) and read next character. Every 4 frames = 8 pixels scrolled = 1 character width.
6DCA INC HL
6DCB LD ($5F7E),HL
6DCE LD A,(HL)
6DCF CP $FF
6DD1 JP Z,reset_scroll_text If $FF (end of text), jump to reset_scroll_text to reset pointer. Otherwise print character via RST $10, reopen upper screen (S) channel (A=2), and fall through to loop.
6DD4 RST $10
6DD5 LD A,$02
6DD7 CALL $1601
6DDA JP overview_loop
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