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Routines |
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Used by the routine at 62700.
Iterates over the 24 three-byte entries in the sprite table at 62808 (Y pixel row at +0 X byte column at +1 attribute byte at +2) to animate the border march effect on the intro screen. For each entry, erases the sprite at its current position (calls XorBlitSprite with bit 7 of E set in shadow to suppress attribute writes), advances the position by one step along a rectangular path (8 pixel rows vertically or 1 byte column horizontally: right across Y=0 down the right side at X=28 left across Y=160 up the left side at X=0), then redraws the sprite at the new position (calls XorBlitSprite with bit 7 clear to write the attribute). Called once per frame by the attract mode loop at 62700.
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| AnimateIntroSprites | 63470 | LD B,24 | B=24 (loop counter: 36 sprite entries). | |
| 63472 | LD HL,62808 | HL=62808 (attribute byte position of the first entry). | ||
| AnimateIntroSprites_Loop | 63475 | LD A,(HL) | A=attribute byte from the current entry. | |
| 63476 | EXX | Switch to shadow; E=attribute byte; SET bit 7 (erase-mode flag for XorBlitSprite); switch back. | ||
| 63477 | LD E,A | |||
| 63478 | SET 7,E | |||
| 63480 | EXX | |||
| 63481 | DEC HL | Back HL two bytes to the Y pixel row (start of entry). | ||
| 63482 | DEC HL | |||
| 63483 | PUSH HL | Stash HL (entry start) and BC on the stack. | ||
| 63484 | PUSH BC | |||
| 63485 | CALL XorBlitSprite | Call XorBlitSprite to erase the sprite at its current position. | ||
| 63488 | POP BC | Restore BC and HL (entry start). | ||
| 63489 | POP HL | |||
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Advance the sprite position by one step along the rectangular border path. Y pixel row is at *(HL), X byte column at *(HL+1). Steps are 8 pixel rows vertically or 1 byte column horizontally. Wraps at X=28 (right boundary, drop down a row) and Y=160 (bottom boundary, scroll left).
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| 63490 | XOR A | A=0. | ||
| 63491 | CP (HL) | If Y position (*HL) = 0 jump to AnimateIntroSprites_ScrollX (top row: scroll X instead of Y). | ||
| 63492 | JR Z,AnimateIntroSprites_ScrollX | |||
| 63494 | INC HL | Read X position (*(HL+1)) and compare with 0; restore HL. | ||
| 63495 | CP (HL) | |||
| 63496 | DEC HL | |||
| 63497 | JR NZ,AnimateIntroSprites_CheckBoundary | If X!=0 jump to AnimateIntroSprites_CheckBoundary. | ||
| 63499 | LD A,(HL) | Y −= 8 (on left side, scroll up); jump to AnimateIntroSprites_Draw. | ||
| 63500 | SUB 8 | |||
| 63502 | LD (HL),A | |||
| 63503 | JR AnimateIntroSprites_Draw | |||
| AnimateIntroSprites_CheckBoundary | 63505 | LD A,160 | A=160; compare with Y position. | |
| 63507 | CP (HL) | |||
| 63508 | JR NZ,AnimateIntroSprites_ScrollDown | If Y!=160 jump to AnimateIntroSprites_ScrollDown (not at bottom boundary, scroll down). | ||
| 63510 | INC HL | X−− (at bottom boundary, scroll left); jump to AnimateIntroSprites_RestoreHL. | ||
| 63511 | DEC (HL) | |||
| 63512 | JR AnimateIntroSprites_RestoreHL | |||
| AnimateIntroSprites_DropRow | 63514 | DEC HL | Back HL to the Y byte. | |
| AnimateIntroSprites_ScrollDown | 63515 | LD A,(HL) | Y += 8 (scroll down); jump to AnimateIntroSprites_Draw. | |
| 63516 | ADD A,8 | |||
| 63518 | LD (HL),A | |||
| 63519 | JR AnimateIntroSprites_Draw | |||
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Top row (Y=0): if X has reached the right boundary (28), drop a row (Y+=8); otherwise scroll right (X++).
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| AnimateIntroSprites_ScrollX | 63521 | INC HL | Read X (*(HL+1)); if X=28 jump to AnimateIntroSprites_DropRow (drop a row); otherwise X++. | |
| 63522 | LD A,(HL) | |||
| 63523 | CP 28 | |||
| 63525 | JR Z,AnimateIntroSprites_DropRow | |||
| 63527 | INC (HL) | X++ (scroll right). | ||
| AnimateIntroSprites_RestoreHL | 63528 | DEC HL | Restore HL to the Y byte position. | |
| AnimateIntroSprites_Draw | 63529 | PUSH HL | Stash HL (entry start) and BC on the stack. | |
| 63530 | PUSH BC | |||
| 63531 | EXX | Switch to shadow; RES bit 7 of E (clear erase-mode flag for draw pass); switch back. | ||
| 63532 | RES 7,E | |||
| 63534 | EXX | |||
| 63535 | CALL XorBlitSprite | Call XorBlitSprite to draw the sprite at the updated position. | ||
| 63538 | POP BC | Restore BC and HL (entry start). | ||
| 63539 | POP HL | |||
| 63540 | INC HL | Advance HL by 5 to the attribute byte of the next entry. | ||
| 63541 | INC HL | |||
| 63542 | INC HL | |||
| 63543 | INC HL | |||
| 63544 | INC HL | |||
| 63545 | DJNZ AnimateIntroSprites_Loop | Decrease counter and loop back to AnimateIntroSprites_Loop. | ||
| 63547 | RET | Return. | ||
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