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Routines |
| Prev: 50045 | Up: Map | Next: 50148 |
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Used by the routines at PrintDateBar, PrintScreenCharacter, RecordResultStorageDecorative, HandleBackspaceKey, PrintARowOfSpaces, ProcessScreenCharacter and UpdateScreenDisplay.
Looks the character up in the font and draws it at the screen address.
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| PrintCharacter | 50056 | PUSH AF | Store that in the low byte and clear the high byte. | |||||||
| 50057 | PUSH BC | |||||||||
| 50058 | PUSH DE | |||||||||
| 50059 | PUSH HL | |||||||||
| 50060 | LD L,A | |||||||||
| 50061 | LD H,0 | |||||||||
| 50063 | ADD HL,HL | Multiply by 8 (each font character is 8 bytes of data). | ||||||||
| 50064 | ADD HL,HL | |||||||||
| 50065 | ADD HL,HL | |||||||||
| 50066 | LD DE,15360 | Point DE at CHARSET minus 256 plus this character's offset. | ||||||||
| 50069 | ADD HL,DE | |||||||||
| 50070 | EX DE,HL | |||||||||
| 50071 | POP HL | Restore the screen address from the stack. | ||||||||
| 50072 | PUSH HL | Keep a copy of it. | ||||||||
| 50073 | LD B,8 | Set a counter in B for 8 bytes of the font data. | ||||||||
| PrintCharacter_0 | 50075 | LD A,(DE) | Read the next byte of this character's bitmap and keep the counters. | |||||||
| 50076 | PUSH BC | |||||||||
| 50077 | PUSH AF | |||||||||
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Does this character need shifting?
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| 50078 | DEC C | See whether this character needs shifting. | ||||||||
| 50079 | INC C | |||||||||
| 50080 | LD B,255 | Go to PrintCharacter_Next if the count reaches zero. | ||||||||
| 50082 | JR Z,PrintCharacter_Next | |||||||||
| PrintCharacter_Loop | 50084 | SRL A | Jump back to PrintCharacter_Loop while the count is not finished. | |||||||
| 50086 | SRL B | |||||||||
| 50088 | DEC C | |||||||||
| 50089 | JR NZ,PrintCharacter_Loop | |||||||||
| PrintCharacter_Next | 50091 | LD C,A | Take the count. | |||||||
| 50092 | LD A,B | |||||||||
| 50093 | CPL | Invert the shifted mask so it covers the screen pixels to keep. | ||||||||
| 50094 | AND (HL) | Keep the screen pixels outside the character. | ||||||||
| 50095 | OR C | Add the pixels of the character. | ||||||||
| 50096 | LD (HL),A | Store it at the pointer. | ||||||||
| 50097 | POP AF | |||||||||
| 50098 | POP BC | |||||||||
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Is the character byte-aligned?
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| 50099 | DEC C | See whether the shift count is zero without changing it, so the character is byte-aligned. | ||||||||
| 50100 | INC C | |||||||||
| 50101 | JR Z,PrintCharacter_NextBitmapByte | Go to PrintCharacter_NextBitmapByte when the shift count is zero, so the character is byte-aligned. | ||||||||
| 50103 | PUSH BC | Work out how many bit positions are left in this row. | ||||||||
| 50104 | PUSH AF | |||||||||
| 50105 | LD A,8 | |||||||||
| 50107 | SUB C | |||||||||
| 50108 | LD C,A | |||||||||
| 50109 | POP AF | |||||||||
| 50110 | LD B,255 | Start a mask of all ones, shifted with the character data. | ||||||||
| PrintCharacter_CountFinished | 50112 | SLA A | Jump back to PrintCharacter_CountFinished while the count is not finished. | |||||||
| 50114 | SLA B | |||||||||
| 50116 | DEC C | |||||||||
| 50117 | JR NZ,PrintCharacter_CountFinished | |||||||||
| 50119 | LD C,A | Take the count. | ||||||||
| 50120 | LD A,B | |||||||||
| 50121 | CPL | Invert the shifted mask so it covers the screen pixels to keep in the next cell. | ||||||||
| 50122 | INC HL | Step to the next character. | ||||||||
| 50123 | AND (HL) | Keep the screen pixels in that cell outside the character. | ||||||||
| 50124 | OR C | Add the part of the character that spills into that cell. | ||||||||
| 50125 | LD (HL),A | Store it at the pointer and step back one character. | ||||||||
| 50126 | DEC HL | |||||||||
| 50127 | POP BC | |||||||||
| PrintCharacter_NextBitmapByte | 50128 | INC DE | Step to the next bitmap byte and the next pixel row. | |||||||
| 50129 | INC H | |||||||||
| 50130 | DJNZ PrintCharacter_0 | Draw the next pixel row and repeat from PrintCharacter_0 until the character is finished. | ||||||||
| 50132 | POP HL | Add 7 to the total. | ||||||||
| 50133 | POP DE | |||||||||
| 50134 | POP BC | |||||||||
| 50135 | LD A,C | |||||||||
| 50136 | ADD A,7 | |||||||||
| 50138 | CP 8 | Jump ahead to PrintCharacter_1 if the total is below 8. | ||||||||
| 50140 | JR C,PrintCharacter_1 | |||||||||
| 50142 | SUB 8 | Drop 8 from the count. | ||||||||
| 50144 | INC L | |||||||||
| PrintCharacter_1 | 50145 | LD C,A | Store the result in the low byte of the count. | |||||||
| 50146 | POP AF | Restore AF from the stack. | ||||||||
| 50147 | RET | Return. | ||||||||
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View the equivalent code in;
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