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Routines |
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This routine is run after each room scenery object/item data set has been set up ready for printing. It:
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| D27D | LD A,($EB4E) | Item properties byte | ||
| D280 | LD C,A | |||
| D281 | AND $07 | Just the lowest 3 bits (bits 0-2) needed for this check | ||
| D283 | CP $05 | Bit 0 (1) = the item is on screen, bit 2 (4) = the item will need erasing | ||
| D285 | JR NZ,$D2AA | If both conditions are met, continue and erase it. Otherwise there's no need so skip the next set of instructions. | ||
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Item is on-screen and needs erasing:
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| D287 | LD A,$00 | Set the draw/erase flag to 0 (ERASE) | ||
| D289 | LD ($EACF),A | |||
| D28C | LD HL,($EACD) | Get address pointer for the item graphic to erase | ||
| D28F | CALL $DB98 | ...And erase the graphic | ||
| D292 | LD A,($EAA8) | Get INK colour of room item/object | ||
| D295 | CP $00 | If it's zero, it's an erased scenery room item (rather than a differently coloured object), so there's no need to specially print colours/attributes for it | ||
| D297 | JR Z,$D29C | |||
| D299 | CALL $E3FD | Otherwise, will need to set the screen attributes/colours for the object | ||
| D29C | LD A,($EAD5) | Get the 'graphic visible' flag (1 = graphic drawn, 0 = graphic not drawn as fully off-screen) | ||
| D29F | LD C,A | ...Store in C register | ||
| D2A0 | LD A,($EB4E) | Get item properties byte | ||
| D2A3 | AND $FE | Filter out (reset) bit 0 | ||
| D2A5 | OR C | ...append the 'graphic visible' flag to bit 0 to indicate if the graphic is on screen or not | ||
| D2A6 | LD ($EB4E),A | ...and re-store | ||
| D2A9 | LD C,A | Copy the item properties byte (EB4E) into the C register | ||
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Check if the item needs drawing
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| D2AA | LD A,($EB43) | Type of graphic to draw | ||
| D2AD | CP $00 | |||
| D2AF | JR Z,$D325 | If this has been set to zero, the item is no longer visible or in existence - there's nothing to draw | ||
| D2B1 | LD A,C | Retrieve item properties byte | ||
| D2B2 | AND $05 | Check for bit 0 (item is visible) and bit 2 (item has moved/needs erasing) | ||
| D2B4 | JR Z,$D325 | If neither is set, there's nothing to draw, so skip the rest of the routine | ||
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Set up item for drawing
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| D2B6 | LD A,($EB4A) | Graphic vertical position within current room, in pixels, from top of room playing area | ||
| D2B9 | LD ($EAD2),A | Copy to working graphics data buffer | ||
| D2BC | LD HL,($EACB) | Graphic's horizontal position, in pixels | ||
| D2BF | LD ($EAD3),HL | Copy to working graphics data buffer | ||
| D2C2 | LD A,($EB4B) | Room type byte - this is set to 64 for 'standard' rooms, or 254/255 for tunnel rooms | ||
| D2C5 | LD ($EAD6),A | Copy to working graphics data buffer | ||
| D2C8 | LD A,$01 | |||
| D2CA | LD ($EACF),A | Set draw/erase flag to 1 (DRAW) | ||
| D2CD | LD A,C | Retrieve item properties byte from C register | ||
| D2CE | AND $02 | Bit 1 (2) if set means item is hidden/not-visible, e.g. inside a chest | ||
| D2D0 | JR Z,$D2D7 | |||
| D2D2 | LD HL,($EAF3) | If this is the case, set the graphics address pointer to the 'dummy' graphic (98B9), so that nothing actually gets drawn | ||
| D2D5 | JR $D315 | As nothing will be drawn, can also skip over the next section dealing with the item's colours/attributes | ||
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Set attribute colours for this item
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| D2D7 | LD A,($EAA8) | Get item colour byte | ||
| D2DA | CP $00 | This is set for interactable items and creatures but 0 for most other things such as scenery (which is drawn with standard room colours) | ||
| D2DC | JR Z,$D312 | If it's set to 0, don't need to print any colours | ||
| D2DE | CP $08 | Is the value 7 or less ('standard' INK colours) | ||
| D2E0 | JR C,$D2E9 | If so, can skip the next 3 instructions | ||
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If bit 3 (8) is set, it means this object flashes (changes colour). Use the game cycle timer to determine its INK colour at this exact moment:
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| D2E2 | LD A,($EAAA) | Get game counter/timer | ||
| D2E5 | AND $03 | Keep just bits 0 and 1 (values = 0-3) | ||
| D2E7 | ADD A,$04 | Add 4, to give an INK value between 4 (green) and 7 (white) | ||
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Set object colour:
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| D2E9 | AND $07 | Only need to keep bits 0-2 (values = 0-7) | ||
| D2EB | OR $40 | Set BRIGHT bit for the colour (all on-screen/viewport colours are set to BRIGHT 1) | ||
| D2ED | LD C,A | Store item (INK) colour in C register | ||
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Check if object graphic INK colour is the same as the current screen PAPER colour (if so, it'd be invisible):
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| D2EE | LD A,($EAA9) | Get room attribute colour | ||
| D2F1 | LD B,A | Temp store in B register | ||
| D2F2 | RRA | Shift bits so that the PAPER colour becomes an INK value to compare | ||
| D2F3 | RRA | |||
| D2F4 | RRA | |||
| D2F5 | AND $07 | Filter out everything other than INK bits | ||
| D2F7 | OR $40 | Set BRIGHT bit | ||
| D2F9 | CP C | Compare with object colour | ||
| D2FA | JR NZ,$D301 | If different, all is fine, skip next two instructions | ||
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Item INK colour is the same as screen PAPER colour.
This shouldn't really happen; most portable objects like keys are light colours (screens have dark backgrounds) and other objects like chests can't be moved from room to room:
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| D2FC | LD HL,($EAF3) | If it does happen, set the graphics address pointer to the 'dummy' graphic (98B9), so nothing gets drawn (the item would appear invisible anyway) | ||
| D2FF | JR $D315 | ...and skip to drawing the actual graphic (pixels) | ||
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As screen PAPER background colours vary, we need to combine the object attribute INK colour with the current screen PAPER colour:
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| D301 | LD A,B | Retrieve the room colour attribute value (stored in PAPER bits) | ||
| D302 | AND $F8 | Filter out/clear any INK bits | ||
| D304 | OR C | Append the item's INK bits (0-7) | ||
| D305 | LD ($EAA8),A | ...and re-store as the item's colour | ||
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Print the item's attribute colours on screen (this is done before drawing the actual pixels):
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| D308 | LD A,($EAD4) | Get the horizontal position high byte - this indicates whether the object is within the current screen viewport | ||
| D30B | CP $00 | |||
| D30D | JR NZ,$D312 | If not, no need to print attributes, skip the next instruction | ||
| D30F | CALL $E3FD | Print screen attribute colours for the room object/creature | ||
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Now draw the item's graphics (pixels):
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| D312 | LD HL,($EB51) | Graphic address pointer | ||
| D315 | CALL $DB98 | Draw the item graphics | ||
| D318 | LD A,($EAD5) | Get the visible graphic flag (1 = graphic drawn, 0 = graphic not drawn as fully off-screen) | ||
| D31B | LD C,A | Append this flag (1/0) into bit 0 of the item properties byte at EB4E indicating whether this item is visible on screen | ||
| D31C | LD A,($EB4E) | |||
| D31F | AND $FE | Filter out bit 0 from the item properties byte | ||
| D321 | OR C | Append a 0 or 1 accordingly (not on-screen/on-screen) | ||
| D322 | LD ($EB4E),A | ...and re-store the item properties byte. | ||
| Prev: D26E | Up: Map | Next: D325 |