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Routines |
| Prev: C7D0 | Up: Map | Next: C837 |
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Used by the routine at D325.
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Get a room data set at 7C00 and copy it into the working buffer at EB43, ready to deal with:
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| C7EA | LD A,(HL) | Check for end-of-data byte | ||||||
| C7EB | CP $FF | |||||||
| C7ED | JP Z,$D331 | If found, skip out of routine | ||||||
| C7F0 | LD BC,$0010 | Prep counter to copy 16 bytes | ||||||
| C7F3 | CP $00 | If the first byte is zero... | ||||||
| C7F5 | JR NZ,$C7FA | |||||||
| C7F7 | ADD HL,BC | ...then this room item is no longer present, so skip to the next data bank of 16 bytes | ||||||
| C7F8 | JR $C7EA | ...and keep checking the data banks | ||||||
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Copy room item data from data bank into working data buffer at EB43
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| C7FA | LD DE,$EB43 | Copy data from 16 byte data bank at 7C00 to EB43 | ||||||
| C7FD | LDIR | |||||||
| C7FF | LD ($EABC),HL | Store address pointer, now at the start of the next 16 byte data set | ||||||
| C802 | LD A,($EB4E) | Item properties byte | ||||||
| C805 | AND %11111011 | Reset bit 2 of this data byte - to indicate this particular room item doesn't needs erasing prior to drawing | ||||||
| C807 | LD ($EB4E),A | ...and restore | ||||||
| C80A | LD HL,($EB51) | Get graphic address pointer to this item's graphics, in the address pointer table at 97C3 | ||||||
| C80D | LD ($EACD),HL | ...and store. | ||||||
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Calculate and store this item's horizontal room co-ordinates. Horizontal half-character (4-pixel) position is converted to pixel position and stored at EAD3.
The carry bit is used in the calculation to store (at EAD4) a flag indicating where the item is in the room, and is set to 0 (visible part of screen), 1 (right of the visible screen) or 255 (left of the visible screen).
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| C810 | LD HL,($EB47) | H = Graphic horizontal position within current room, in half character (4 pixel) steps (H = EB48, L = EB47). L contains an overflow from this. | ||||||
| C813 | ADD HL,HL | x 2 | ||||||
| C814 | SBC A,A | If carry set, set A to 255, otherwise 0 | ||||||
| C815 | ADD HL,HL | x 4 to complete conversion of horizontal position from half-characters to pixels | ||||||
| C816 | RLA | If carry set, rotate carry bit into A register | ||||||
| C817 | LD ($EAD4),A | ...and store as the high byte, e.g. 0 = in room viewport, 1 = to the right of the viewport, 255 = to the left of the viewport | ||||||
| C81A | LD A,H | Get horizontal screen pixel position | ||||||
| C81B | LD ($EAD3),A | ...and store. | ||||||
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The next instructions check bit 4 of the Graphic properties byte (this bit is unused).
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| C81E | LD A,($EB4F) | This is the pre-graphics data byte (Graphic properties) | ||||||
| C821 | AND $10 | Check if bit 4 set (16) | ||||||
| C823 | JR Z,$C837 | If it's NOT set, jump to C837 | ||||||
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None of the graphics has bit 4 (16) set, so these instructions aren't run (which add an offset to the graphic address pointer):
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| C825 | LD HL,($EB51) | --- | ||||||
| C828 | ADD HL,DE | --- | ||||||
| C829 | ADD HL,DE | --- | ||||||
| C82A | LD ($EB51),HL | --- | ||||||
| C82D | LD A,($EB4E) | --- | ||||||
| C830 | OR $04 | --- | ||||||
| C832 | LD ($EB4E),A | --- | ||||||
| C835 | JR $C841 | --- | ||||||
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