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Routines |
Prev: 27671 | Up: Map | Next: 27803 |
Byte | Contents |
---|---|
1 | y-coordinate |
2 | x-coordinate |
3 | UDG reference |
4 (bits 0-3) | BRIGHT/PAPER attributes |
4 (bits 6 & 7) | UDG base page identifier |
Address | Object |
---|---|
56637 | Left study door (closed) |
56893 | Left study door (open) |
57088 | Right study door (closed) |
57344 | Right study door (open) |
56576 | Science Lab storeroom door (closed) |
56832 | Science Lab storeroom door (open) |
57149 | Boys' skool door (closed) |
57405 | Boys' skool door (open) |
63744 | Skool gate (closed) |
64000 | Skool gate (open) |
56064 | Drinks cabinet door (closed) |
56320 | Drinks cabinet door (open) |
55040 | Top floor window (closed) |
55296 | Top floor window (open) |
55552 | Middle floor window (closed) |
55808 | Middle floor window (open) |
56081 | Cups in boys' skool (empty) |
56694 | Leftmost cup in boys' skool (containing water) |
56699 | Leftmost cup in boys' skool (containing sherry) |
56950 | Middle cup in boys' skool (containing water) |
56955 | Middle cup in boys' skool (containing sherry) |
57206 | Rightmost cup in boys' skool (containing water) |
57211 | Rightmost cup in boys' skool (containing sherry) |
56337 | Cup in girls' skool (empty) |
57462 | Cup in girls' skool (containing water) |
57467 | Cup in girls' skool (containing sherry) |
57600 | Tree (with no bike attached) |
57856 | Tree (with bike attached) |
HL | Start address of table corresponding to door/window/cup/bike |
27672 | LD A,(HL) | Pick up the y-coordinate (Y) in D |
27673 | LD D,A | |
27674 | INC A | Return if we found the end-of-table marker (255) |
27675 | RET Z | |
27676 | INC HL | Point HL at byte 2 of this table entry |
27677 | LD E,(HL) | Pick up the x-coordinate (X) in E |
27678 | INC HL | Point HL at byte 3 of this table entry |
27679 | PUSH HL | |
27680 | LD A,(32767) | C=leftmost column of play area on screen |
27683 | LD C,A | |
27684 | LD A,E | Jump if (X,Y) is off-screen (no need to update the screen refresh buffer) |
27685 | SUB C | |
27686 | JR C,27717 | |
27688 | CP 32 | |
27690 | JR NC,27717 | |
(X,Y) corresponds to a location that is currently on-screen, so we have to update the screen refresh buffer (SRB).
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27692 | LD C,A | 0<=C<=31 (column of screen) |
27693 | AND 7 | Point HL at an entry in the 8-byte table at 57720, whose contents are (128, 64, 32, 16, 8, 4, 2, 1) |
27695 | ADD A,120 | |
27697 | LD L,A | |
27698 | LD H,225 | |
27700 | LD B,(HL) | Pick up this entry in B |
27701 | LD A,C | 0<=A<=31 (column of screen) |
27702 | RRCA | Point HL at the byte of the SRB corresponding to (X,Y) |
27703 | RRCA | |
27704 | RRCA | |
27705 | AND 3 | |
27707 | ADD A,D | |
27708 | ADD A,D | |
27709 | ADD A,D | |
27710 | ADD A,D | |
27711 | LD L,A | |
27712 | LD H,127 | |
27714 | LD A,(HL) | Set the appropriate bit in the SRB byte |
27715 | OR B | |
27716 | LD (HL),A | |
The UDG reference (i.e. the LSB of the base address of the skool UDG) for the skool location (X,Y) must be modified to reflect the change in status of the door, window, cup or bike.
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27717 | LD L,E | Point HL at the Q value (0<=Q<=143) in page 181 for the x-coordinate X (see 24684) |
27718 | LD H,181 | |
27720 | LD E,(HL) | Pick up the Q value in E |
27721 | LD A,D | Set DE to the address where the UDG reference for (X,Y) is stored |
27722 | ADD A,160 | |
27724 | LD D,A | |
27725 | POP HL | Point HL at byte 3 of the table entry |
27726 | LD A,(HL) | Pick up the replacement UDG reference in A |
27727 | INC HL | Point HL at byte 4 of the table entry |
27728 | LD (DE),A | Replace the UDG reference for the skool location (X,Y) with the one collected from the table entry |
The attribute byte for the skool location (X,Y) must be modified too.
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27729 | LD A,(HL) | Pick up byte 4 of the table entry in A |
27730 | AND 15 | Keep only bits 0-3 (the BRIGHT and PAPER attributes) |
27732 | LD B,A | Copy them to B |
27733 | LD A,E | A=Q (0<=Q<=143) |
27734 | LD C,A | Save the Q value in C for later |
27735 | ADD A,104 | Point DE at byte 180+INT(Q/2) of page Y+160, where the BRIGHT and PAPER attributes for the skool location (X,Y) are stored |
27737 | SCF | |
27738 | RRA | |
27739 | LD E,A | |
27740 | JR C,27753 | Jump if Q is odd (BRIGHT and PAPER in bits 0-3) |
27742 | LD A,B | Shift the BRIGHT and PAPER attributes from bits 0-3 to bits 4-7 of B |
27743 | RRCA | |
27744 | RRCA | |
27745 | RRCA | |
27746 | RRCA | |
27747 | LD B,A | |
27748 | LD A,(DE) | Pick up the current attribute byte for the skool location (X,Y), keeping bits 0-3 as they are |
27749 | AND 15 | |
27751 | JR 27756 | Jump forward to adjust bits 4-7 appropriately |
27753 | LD A,(DE) | Pick up the current attribute byte for the skool location (X,Y), keeping bits 4-7 as they are |
27754 | AND 240 | |
27756 | OR B | Adjust bits 0-3 (if Q is odd) or bits 4-7 (Q is even) of the attribute byte for the skool location (X,Y) |
27757 | LD (DE),A | |
Finally, the base page (128, 136, 144 or 152) for the new skool UDG reference must be set.
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27758 | LD A,(HL) | Pick up byte 4 of the table entry in A again |
27759 | AND 192 | Keep only bits 6 and 7 |
27761 | BIT 6,A | Set B=10001000 if these bits are 11, 10000000 (10), 00001000 (01) or 00000000 (00) |
27763 | JR Z,27767 | |
27765 | SUB 56 | |
27767 | LD B,A | |
27768 | LD A,C | A=Q |
27769 | LD C,136 | C=10001000 |
27771 | SRL A | Set A=INT(Q/4), and shift B and C right (Q AND 3) times |
27773 | JR NC,27779 | |
27775 | RRC B | |
27777 | RRC C | |
27779 | SRL A | |
27781 | JR NC,27791 | |
27783 | RRC B | |
27785 | RRC C | |
27787 | RRC B | |
27789 | RRC C | |
27791 | ADD A,144 | Point DE at byte 144+INT(Q/4) of page Y+160, where the UDG MSB identifier bit-pair for skool location (X,Y) is held (see 24684) |
27793 | LD E,A | |
27794 | LD A,(DE) | Pick up the current MSB identifier byte in A |
27795 | OR C | Replace bits (0,4), (1,5), (2,6) or (3,7) in this byte with the corresponding bits in B |
27796 | XOR C | |
27797 | OR B | |
27798 | LD (DE),A | Store the new MSB identifier byte |
Move to the next entry in the table.
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27799 | INC HL | Point HL at the first byte of the next entry in the table |
27800 | JP 27672 | Jump back to process it |
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