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Routines |
H | Character number (152-169) |
28994 | CALL 28882 | A=next character in the message being written |
28997 | LD B,A | Save this in B briefly |
28998 | CALL 28968 | A=identifier of the blackboard being written on |
29001 | LD C,A | Transfer this to C |
29002 | LD A,B | A=next character in the message being written |
29003 | LD B,127 | Point BC at the appropriate blackboard buffer |
29005 | AND A | Is the message finished? |
29006 | JR NZ,29012 | Jump if not |
29008 | DEC A | A=255 |
29009 | LD (BC),A | Store the pixel coordinates of the next character to be written on the board |
29010 | INC A | Set the zero flag if the message is finished |
29011 | RET |
29012 | CP 2 | Is it newline? |
29014 | JR NZ,29023 | Jump if not |
29016 | LD A,(BC) | Pick up the contents of 32748 (Reading Room blackboard), 32750 (White Room blackboard) or 32752 (Exam Room blackboard) and set it to 0 (start of top line) or 64 (start of bottom line) |
29017 | AND 64 | |
29019 | XOR 64 | |
29021 | JR 29009 |
29023 | PUSH HL | |
29024 | LD L,A | Point HL at the address holding the pixel width of the character to be written on the board |
29025 | LD H,217 | |
29027 | LD A,(BC) | A=pixel coordinates (0-127) of the location at which the character will be written |
29028 | AND 63 | Discard bit 6 (the line indicator bit) |
29030 | ADD A,192 | Set the carry flag if there is not enough space at the end of the current line to print the character |
29032 | SCF | |
29033 | ADC A,(HL) | |
29034 | LD A,(BC) | A=pixel coordinates (0-127) |
29035 | JR NC,29042 | Jump if there is enough space to print the character on the current line |
29037 | AND 64 | Otherwise toggle which line (top or bottom) to write on and reset the pixel x-coordinate to 0 (start of the line) |
29039 | XOR 64 | |
29041 | LD (BC),A | |
29042 | RRCA | Compute the skool coordinates of the location of the character to be written and store them in DE |
29043 | RRCA | |
29044 | RRCA | |
29045 | AND 15 | |
29047 | CP 8 | |
29049 | JR C,29054 | |
29051 | INC D | |
29052 | AND 7 | |
29054 | ADD A,E | |
29055 | LD E,A | |
29056 | CALL 28807 | Update the screen refresh buffer for these coordinates |
29059 | LD A,(BC) | Modify the RES n,(HL) instruction at 29102 below, which in effect draws a white pixel (of chalk) at the appropriate spot |
29060 | AND 7 | |
29062 | ADD A,A | |
29063 | ADD A,A | |
29064 | ADD A,A | |
29065 | CPL | |
29066 | SUB 65 | |
29068 | LD (29103),A | |
29071 | LD A,(BC) | Compute the pixel x-coordinate (0-63) of the rightmost pixel column of the character to be written on the board, and store it in the blackboard buffer |
29072 | ADD A,(HL) | |
29073 | INC A | |
29074 | LD (BC),A | |
29075 | LD C,(HL) | C=pixel width of theh character to be written on the board |
29076 | EX DE,HL | Point HL at the skool UDG reference of the character square of the blackboard that will be written on and pick it up in L |
29077 | LD A,(HL) | |
29078 | LD L,A |
29079 | LD H,128 | Point HL at the graphic data for the skool UDG reference in A; the skool UDG references are 206-191 for the Reading Room board, 238-223 for the White Room board, and 222-207 for the Exam Room board, decreasing from left to right |
29081 | CP 233 | |
29083 | JR NC,29095 | |
29085 | CP 231 | |
29087 | JR NC,29093 | |
29089 | CP 225 | |
29091 | JR NC,29095 | |
29093 | LD H,136 | |
29095 | INC D | A=next pixel column of the character to be written on the board |
29096 | LD A,(DE) | |
29097 | LD B,8 | There are 8 pixels in a pixel column |
29099 | RLCA | Draw the pixel column on the blackboard by directly resetting bits in the skool graphic data; any bits already reset by previous writing remain reset |
29100 | JR NC,29104 | |
29102 | RES n,(HL) | |
29104 | INC H | |
29105 | DJNZ 29099 | |
29107 | DEC C | Next pixel column |
29108 | JR Z,29134 | Jump if we've finished drawing the character on the board |
29110 | LD A,H | Point HL back at the top pixel row of the skool UDG data |
29111 | SUB 8 | |
29113 | LD H,A | |
29114 | LD A,(29103) | Modify the RES n,(HL) instruction at 29102 above to RES m,(HL) where m=n-1 (mod 8), effectively moving one pixel column to the right |
29117 | OR 64 | |
29119 | SUB 8 | |
29121 | AND 191 | |
29123 | LD (29103),A | |
29126 | CP 190 | Did we wrap round from bit 0 to bit 7? |
29128 | JR NZ,29095 | Continue drawing pixel columns in this character square if not |
29130 | DEC L | A=skool UDG reference of the next character square to the right on the blackboard |
29131 | LD A,L | |
29132 | JR 29079 | Draw the next pixel column in the next character square |
29134 | INC C | Reset the zero flag to indicate that the message isn't finished |
29135 | POP HL | Restore the character number to H |
29136 | RET |