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44561: ScreenTransition
Animated wipe-to-black transition between screens. Progressively sets each of the 24 attribute rows to 0 (black-on-black, making text invisible) with a one-frame delay between rows, creating a top-to-bottom blackout animation. After all 24 rows are zeroed, clears the display file and resets attributes to 7 (white ink on black paper) ready for the next screen.
Used by the routines at 36457, 44125 and 44524.
44561 LD HL,22528 HL = 22528 (start of attribute file)
44564 XOR A A = 0 (black-on-black attribute)
44565 LD B,24 24 character rows to wipe
44567 PUSH BC save row counter
44568 LD B,32 32 attribute columns per row
44570 LD (HL),A write black-on-black: text becomes invisible
44571 INC HL
44572 DJNZ 44570 fill entire character row
44574 PUSH HL save attribute pointer
44575 CALL 36448 one-frame delay (~20ms): visible wipe effect
44578 POP HL
44579 POP BC
44580 DJNZ 44567 next row
44582 CALL 42501 ClearDisplay: blank all pixels
44585 LD A,7 white ink on black paper
44587 CALL 42515 FillAttributes(7): restore normal attributes
44590 RET
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