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87CA: Display the title screen and play the theme tune
Used by the routines at 869F, 89AD and 8C4A.
The first thing this routine does is initialise some game status buffer variables in preparation for the next game.
Input
Output
87CA XOR A A=0
87CB LD ($85CE),A Initialise the Kempston joystick indicator at 85CE
87CE LD ($85E1),A Initialise the in-game music note index at 85E1
87D1 LD ($85CD),A Initialise the (unused) screen flash counter at 85CD
87D4 LD ($85D1),A Initialise the airborne status indicator at 85D1
87D7 LD ($85CB),A Initialise the minute counter at 85CB
87DA LD ($85E0),A Initialise the inactivity timer at 85E0
87DD LD ($85DF),A Initialise the game mode indicator at 85DF
87E0 LD A,$07 Initialise the number of lives remaining at 85CC
87E2 LD ($85CC),A
87E5 LD A,$D0 Initialise Willy's pixel y-coordinate at 85CF
87E7 LD ($85CF),A
87EA LD A,$21 Initialise the current room number at 8420 to 0x21 (The Bathroom)
87EC LD ($8420),A
87EF LD HL,$5DB4 Initialise Willy's coordinates at 85D3 to (13,20)
87F2 LD ($85D3),HL
87F5 LD HL,$857C Initialise the number of items collected at 857C to "000"
87F8 LD (HL),$30
87FA INC HL
87FB LD (HL),$30
87FD INC HL
87FE LD (HL),$30
8800 LD H,$A4 Page 0xA4 holds the first byte of each entry in the item table
8802 LD A,($A3FF) Pick up the index of the first item from A3FF
8805 LD L,A Point HL at the entry for the first item
8806 LD ($85DE),A Initialise the counter of items remaining at 85DE
8809 SET 6,(HL) Set the collection flag for every item in the item table at A400
880B INC L
880C JR NZ,$8809
880E LD HL,$85E2 Initialise the keypress flag in bit 0 at 85E2
8811 SET 0,(HL)
Next, prepare the screen.
8813 LD HL,$4000 Clear the entire display file
8816 LD DE,$4001
8819 LD BC,$17FF
881C LD (HL),$00
881E LDIR
8820 LD HL,$9800 Copy the attribute bytes for the title screen from 9800 and 9A00 to the attribute file
8823 LD BC,$0300
8826 LDIR
8828 LD HL,$5A60 Copy the attribute value 0x46 (INK 6: PAPER 0: BRIGHT 1) into the row of 32 cells from (19,0) to (19,31) on the screen
882B LD DE,$5A61
882E LD BC,$001F
8831 LD (HL),$46
8833 LDIR
8835 LD IX,$8454 Print "+++++ Press ENTER to Start +++++" (see 8454) at (19,0)
8839 LD DE,$5060
883C LD C,$20
883E CALL $9680
8841 LD DE,$5800 Point DE at the first byte of the attribute file
The following loop scans the top two-thirds of the attribute file, which contains values 0x00, 0x04, 0x05, 0x08, 0x09, 0x24, 0x25, 0x28, 0x29, 0x2C, 0x2D and 0xD3 (copied from 9800). Whenever a value other than 0x00, 0x09, 0x24, 0x2D or 0xD3 is found, a triangle UDG is drawn at the corresponding location in the display file.
8844 LD A,(DE) Pick up a byte from the attribute file
8845 OR A Is it 0x00 (INK 0: PAPER 0)?
8846 JR Z,$888E If so, jump to consider the next byte in the attribute file
8848 CP $D3 Is it 0xD3 (INK 3: PAPER 2: BRIGHT 1: FLASH 1)?
884A JR Z,$888E If so, jump to consider the next byte in the attribute file
884C CP $09 Is it 0x09 (INK 1: PAPER 1)?
884E JR Z,$888E If so, jump to consider the next byte in the attribute file
8850 CP $2D Is it 0x2D (INK 5: PAPER 5)?
8852 JR Z,$888E If so, jump to consider the next byte in the attribute file
8854 CP $24 Is it 0x24 (INK 4: PAPER 4)?
8856 JR Z,$888E If so, jump to consider the next byte in the attribute file
8858 LD C,$00 C=0; this will be used as an offset from the triangle UDG base address (8431)
885A CP $08 Is the attribute value 0x08 (INK 0: PAPER 1)?
885C JR Z,$8871 Jump if so
885E CP $29 Is it 0x29 (INK 1: PAPER 5)?
8860 JR Z,$8871 Jump if so
8862 CP $2C Is it 0x2C (INK 4: PAPER 5)?
8864 JR Z,$886E Jump if so
8866 CP $05 Is it 0x05 (INK 5: PAPER 0)?
8868 JR Z,$8871 Jump if so
886A LD C,$10 Set the triangle UDG offset to 0x10
886C JR $8871
886E LD A,$25 Change the attribute byte here from 0x2C (INK 4: PAPER 5) to 0x25 (INK 5: PAPER 4)
8870 LD (DE),A
8871 LD A,E Point HL at the triangle UDG to draw (8431, 8439, 8441 or 8449)
8872 AND $01
8874 RLCA
8875 RLCA
8876 RLCA
8877 OR C
8878 LD C,A
8879 LD B,$00
887B LD HL,$8431
887E ADD HL,BC
887F PUSH DE Save the attribute file address briefly
8880 BIT 0,D Set the zero flag if we're still in the top third of the attribute file
8882 LD D,$40 Point DE at the top third of the display file
8884 JR Z,$8888 Jump if we're still in the top third of the attribute file
8886 LD D,$48 Point DE at the middle third of the display file
8888 LD B,$08 There are eight pixel rows in a triangle UDG
888A CALL $969B Draw a triangle UDG on the screen
888D POP DE Restore the attribute file address to DE
888E INC DE Point DE at the next byte in the attribute file
888F LD A,D Have we finished scanning the top two-thirds of the attribute file yet?
8890 CP $5A
8892 JP NZ,$8844 If not, jump back to examine the next byte
Now check whether there is a joystick connected.
8895 LD BC,$001F This is the joystick port
8898 DI Disable interrupts (which are already disabled)
8899 XOR A A=0
889A IN E,(C) Combine 256 readings of the joystick port in A; if no joystick is connected, some of these readings will have bit 5 set
889C OR E
889D DJNZ $889A
889F AND $20 Is a joystick connected (bit 5 reset)?
88A1 JR NZ,$88A8 Jump if not
88A3 LD A,$01 Set the Kempston joystick indicator at 85CE to 1
88A5 LD ($85CE),A
And finally, play the theme tune and check for keypresses.
88A8 LD HL,$85FB Point HL at the theme tune data at 85FB
88AB CALL $96A2 Play the theme tune
88AE JP NZ,$88FC Start the game if ENTER, 0 or the fire button was pressed
88B1 XOR A Initialise the temporary game status buffer variable at 85E4 to 0; this will be used as an index for the message scrolled across the screen (see 8454)
88B2 LD ($85E4),A
88B5 CALL $8AEB Cycle the INK and PAPER colours
88B8 LD HL,$5A60 Copy the attribute value 0x4F (INK 7: PAPER 1: BRIGHT 1) into the row of 32 cells from (19,0) to (19,31) on the screen
88BB LD DE,$5A61
88BE LD BC,$001F
88C1 LD (HL),$4F
88C3 LDIR
88C5 LD A,($85E4) Pick up the message index from 85E4
88C8 LD IX,$8454 Point IX at the corresponding location in the message at 8454
88CC LD E,A
88CD LD D,$00
88CF ADD IX,DE
88D1 LD DE,$5060 Print 32 characters of the message at (19,0)
88D4 LD C,$20
88D6 CALL $9680
88D9 LD A,($85E4) Prepare a value between 0x32 and 0x51 in A (for the routine at 96DE)
88DC AND $1F
88DE ADD A,$32
88E0 CALL $96DE Make a sound effect
88E3 LD BC,$AFFE Read keys H-J-K-L-ENTER and 6-7-8-9-0
88E6 IN A,(C)
88E8 AND $01 Keep only bit 0 of the result (ENTER, 0)
88EA CP $01 Was ENTER or 0 pressed?
88EC JR NZ,$88FC Jump if so to start the game
88EE LD A,($85E4) Pick up the message index from 85E4
88F1 INC A Increment it
88F2 CP $E0 Set the zero flag if we've reached the end of the message
88F4 LD ($85E4),A Store the new message index at 85E4
88F7 JR NZ,$88B5 Jump back unless we've finished scrolling the message across the screen
88F9 JP $8813 Jump back to prepare the screen and play the theme tune again
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