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755A: Write a line of text into a graphic buffer
Used by the routines at 75CC, 7600, 7940 and F9A5. Writes a line of text into a graphic buffer (at EB00, EC00 or ED00) and centres it.
DE Buffer address
HL Message address
755A XOR A Clear the buffer ready for writing
755B LD B,$40
755D LD (DE),A
755F DJNZ $755D
7561 DEC DE Point DE at the last byte of the buffer
7562 LD C,$3E There are 62 pixel columns available for writing in
7564 LD A,(HL) Pick up a character from the message in A
7565 INC HL Move to the next character in the message
7566 AND A Have we reached the end of the message?
7567 JR Z,$757F Jump if so
7569 PUSH HL Save the message pointer
756A LD L,A Point HL at the pixel width of the bitmap for the character in A
756B LD H,$D9
756D LD A,(HL) Pick up the width in A
756E LD B,A Transfer the width to B
756F INC H Point HL at the next font character bitmap byte
7570 LD A,(HL) Pick this up in A
7571 CALL $7591 Insert the font character bitmap byte into the buffer
7574 DEC C Decrease the pixel column count
7575 DJNZ $756F Jump back until all pixel columns for this letter are done
7577 XOR A A=0 (empty vertical pixel column, i.e. space)
7578 DEC C Decrease the pixel column count
7579 CALL $7591 Insert the space into the buffer
757C POP HL Restore the message pointer to HL
757D JR $7564 Jump back to write the next letter from the message
We've finished writing the message. Now centre it.
757F BIT 7,C Did we use more than 62 pixel columns?
7581 RET NZ Return if so
7582 RR C C holds the number of unused pixel columns; halve this and add one to get the padding
7584 INC C
7585 XOR A Insert an empty pixel column (space)
7586 CALL $7591
7589 DEC C Next column of padding
758A JR NZ,$7585 Jump back until the text has been centred
758C RET
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