Routines
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E4F7: Move an object to a new position, and its sprite on the screen with it
Used by the routines at PLACE_FROM_TEMPLATE, CREATURE_UPDATE, ANIMATE_AND_MOVE and BUMPED.
Krumlinde's RTN_Iso_Project. The new position is compared with the record's (+6 to +8), field by field, and the sprite's place on the screen (+0, +1) moved by the difference, projected: a step along +6 moves it one pixel right and half a row up, a step along +8 one pixel left and half a row up, and a step up in +7 (the height) one row up. So, give or take a constant, x is +6 less +8 and y is (+6 plus +8) / 2 plus +7, and the far corner of a room is at the top of the screen.
Half rows are rounded towards zero, and C remembers whether +6's half was rounded: when both +6 and +8 move an odd amount the same way, the two halves make a whole row between them. An odd move along one axis alone would lose its half row, but the knight moves two at a step (measured, walking each way in the simulator: x by 2 and y by 1 a step).
Called when an object is made for a room (PLACE_FROM_TEMPLATE, after setting its record to 50, its height plus 50, 50, the position its template's screen place is drawn for) and when things move (CREATURE_UPDATE, ANIMATE_AND_MOVE, BUMPED).
Input
IX The object's record
B The new +6
D The new +7 (the height of its top)
H The new +8
ISO_MOVE E4F7 PUSH HL Keep H, the new +8; HL: the sprite's place on the screen, x and y.
E4F8 LD C,$00
E4FA LD L,(IX+OBJ_SCREEN_X)
E4FD LD H,(IX+OBJ_SCREEN_Y)
E500 LD A,B How far +6 moves (not at all: on to the height).
E501 SUB (IX+OBJ_X)
E504 JR Z,ISO_MOVE_3
E506 LD E,A Further: half of it, rounded down; bit 0 of C set if it was odd.
E507 JR C,ISO_MOVE_0
E509 SRL A
E50B JR NC,ISO_MOVE_2
E50D SET 0,C
E50F JR ISO_MOVE_2
ISO_MOVE_0 E511 NEG Back: half of it, rounded towards zero; bit 1 of C set if it was odd.
E513 SRL A
E515 JR NC,ISO_MOVE_1
E517 SET 1,C
ISO_MOVE_1 E519 NEG
ISO_MOVE_2 E51B ADD A,H y up by the half, x right by the whole; the new +6.
E51C LD H,A
E51D LD A,E
E51E ADD A,L
E51F LD L,A
E520 LD (IX+OBJ_X),B
ISO_MOVE_3 E523 LD A,D y up by the change in the height; the new +7.
E524 SUB (IX+OBJ_TOP)
E527 ADD A,H
E528 LD H,A
E529 LD (IX+OBJ_TOP),D
E52C POP DE How far +8 moves.
E52D LD A,D
E52E SUB (IX+OBJ_Z)
E531 LD E,A
E532 JR C,ISO_MOVE_4 Further: half of it, and a row more if +6 moved an odd amount the same way.
E534 SRL A
E536 JR NC,ISO_MOVE_6
E538 BIT 0,C
E53A JR Z,ISO_MOVE_6
E53C INC A
E53D JR ISO_MOVE_6
ISO_MOVE_4 E53F NEG Back: the same, the other way.
E541 SRL A
E543 JR NC,ISO_MOVE_5
E545 BIT 1,C
E547 JR Z,ISO_MOVE_5
E549 INC A
ISO_MOVE_5 E54A NEG
ISO_MOVE_6 E54C ADD A,H y up by the half, x left by the whole.
E54D LD H,A
E54E LD A,L
E54F SUB E
E550 LD L,A
E551 LD (IX+OBJ_Z),D The new +8, and the sprite's new place.
E554 LD (IX+OBJ_SCREEN_X),L
E557 LD (IX+OBJ_SCREEN_Y),H
E55A RET
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