Routines
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6B1B: Write a line of text into a graphic buffer
Used by the routines at 50B9 and 6B46. Writes a line of text into a graphic buffer (at 5B00 or E428) and centres it.
Input
6B1B LD (\$D60B),DE Save the message address in bytes 0x0B and 0x0C of the character buffer in page 0xD6
This entry point is used by the routine at 6B46 to write the second line of text into the message box graphic buffer at E428.
6B1F PUSH HL Copy the buffer address to HL'
6B20 EXX
6B21 POP HL
6B22 LD BC,\$0000 B=0 (during startup) or 64, C=0 (this instruction is set to LD BC,\$4000 before the game starts; see 53A0)
6B25 LD (HL),C Create 64 (or 256) empty pixel columns in the buffer
6B26 INC HL
6B27 DJNZ \$6B25
6B29 DEC HL
6B2A EXX
6B2B LD H,\$D6 We are using the character buffer in page 0xD6 to process the message
6B2D LD C,\$FF The message box is 255 (during startup) or 64 pixels wide (this instruction is set to LD C,\$40 before the game starts; see 53A0)
6B2F CALL \$66CE A=ASCII code of the next character in the message
6B32 CP \$03 Is the ASCII code 0, 1 or 2 (end of line)?
6B34 JR C,\$6B3B Jump if so to centre the text
6B36 CALL \$69E6 Slide the bitmap for CHR\$(A) into the buffer
6B39 JR \$6B2F Jump back to do the next character
6B3B SRL C Now C=half the number of unused pixel columns left in the buffer
6B3D RET Z Return if this is zero (the buffer is full)
6B3E CALL \$69F4 Create C empty pixel columns in the buffer, thus centring the message
6B41 DEC C
6B42 JR NZ,\$6B3E
6B44 RET
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