|
Routines |
| Prev: 25596 | Up: Map | Next: 25931 |
|
Used by the routine at PlotCharacter.
Draws character A at the print position, using the ROM font. The eight bytes are shifted into whichever pixel column the cursor occupies inside its display byte, then ORed into the screen.
|
||||
|
The ROM character set lives at Character set. Subtracting 256 makes the character code times 8 land on its glyph.
|
||||
| PlotGlyph | 25731 | LD DE,(23431) | Keep the screen address. The font is the ROM character set minus 256. | |
| 25735 | LD BC,15360 | |||
| 25738 | LD H,0 | Character A, widened. | ||
| 25740 | LD L,A | |||
| 25741 | ADD HL,HL | Times eight, plus the font base. | ||
| 25742 | ADD HL,HL | |||
| 25743 | ADD HL,HL | |||
| 25744 | ADD HL,BC | |||
| 25745 | PUSH DE | The screen address and the glyph address are restored after the copy. | ||
| 25746 | PUSH HL | |||
| 25747 | LD DE,27427 | The eight glyph bytes are copied into GlyphBuffer. C starts clear. | ||
| 25750 | LD BC,2048 | |||
| PlotGlyph_Copy | 25753 | LD A,(HL) | Copy one byte of the glyph. | |
| 25754 | LD (DE),A | |||
| 25755 | INC HL | |||
| 25756 | INC DE | |||
| 25757 | BIT 1,A | Bit 1 of a byte marks a descender. | ||
| 25759 | JR Z,PlotGlyph_Copied | |||
| 25761 | LD C,255 | |||
| PlotGlyph_Copied | 25763 | DJNZ PlotGlyph_Copy | The next byte. | |
|
Tip the glyph so it sits in the right-hand pixels of its byte. A descender in the source sets the marker in C.
|
||||
| PlotGlyph_Align | 25765 | LD DE,27427 | Eight glyph bytes are shifted in GlyphBuffer. | |
| 25768 | LD B,8 | |||
| PlotGlyph_Row | 25770 | LD A,(DE) | A source bit carried out sets the top bit. | |
| 25771 | RLA | |||
| 25772 | JR NC,PlotGlyph_Nibble | |||
| 25774 | OR 128 | |||
| PlotGlyph_Nibble | 25776 | BIT 0,C | The descender marker shifts the glyph one place further. | |
| 25778 | JR Z,PlotGlyph_Mask | |||
| 25780 | LD H,A | Split the byte into nibbles. | ||
| 25781 | AND 15 | |||
| 25783 | LD L,A | |||
| 25784 | LD A,H | The low nibble moves into the neighbouring byte. | ||
| 25785 | AND 240 | |||
| 25787 | RL L | |||
| 25789 | OR L | |||
| PlotGlyph_Mask | 25790 | AND 252 | Store the aligned byte and do the next row. | |
| 25792 | LD (DE),A | |||
| 25793 | INC DE | |||
| 25794 | DJNZ PlotGlyph_Row | |||
| 25796 | POP HL | Restore the glyph address and the screen address from the stack. | ||
| 25797 | POP DE | |||
| 25798 | LD HL,27427 | Point DE at the buffer and HL at the screen byte. | ||
| 25801 | EX DE,HL | |||
| 25802 | PUSH HL | |||
|
The column within the byte chooses how the shifted glyph is merged with the pixels already there.
|
||||
| PlotGlyph_Column | 25803 | LD A,(23434) | The column within the byte is 0, 1, 2 or 3. | |
| 25806 | AND 3 | |||
| 25808 | DEC A | Column 1 uses the two-pixel shift. | ||
| 25809 | JR Z,PlotGlyph_Byte1 | |||
| 25811 | DEC A | Column 2 uses the four-pixel shift. | ||
| 25812 | JR Z,PlotGlyph_Byte2 | |||
| 25814 | DEC A | Column 3 keeps the top two pixels. | ||
| 25815 | JR Z,PlotGlyph_Byte3 | |||
| 25817 | LD B,8 | Column 0 copies eight fresh bytes. | ||
| PlotGlyph_Byte0 | 25819 | LD A,(DE) | Copy one glyph byte and step to the next pixel row. | |
| 25820 | LD (HL),A | |||
| 25821 | INC DE | |||
| 25822 | INC H | |||
| 25823 | DJNZ PlotGlyph_Byte0 | All eight bytes. | ||
| PlotGlyph_Stored | 25825 | POP HL | The print address moves on one byte. | |
| 25826 | INC HL | |||
| 25827 | LD (23431),HL | |||
| 25830 | JR PlotGlyph_Advance | Join PlotGlyph_Advance to advance the column. | ||
| PlotGlyph_Byte1 | 25832 | LD B,8 | Eight pixel rows. | |
| PlotGlyph_Shift2 | 25834 | LD A,(DE) | Take the glyph byte and the previous screen byte. | |
| 25835 | DEC HL | |||
| 25836 | SRL (HL) | Make room for two pixels. | ||
| 25838 | SRL (HL) | |||
| 25840 | SLA A | Shift two pixels of the glyph in. | ||
| 25842 | RL (HL) | |||
| 25844 | SLA A | |||
| 25846 | RL (HL) | |||
| 25848 | INC HL | Store the shifted byte. | ||
| 25849 | LD (HL),A | |||
| 25850 | INC H | The next pixel row. | ||
| 25851 | INC DE | |||
| 25852 | DJNZ PlotGlyph_Shift2 | All eight. | ||
| 25854 | JR PlotGlyph_Stored | Join the shared advance at PlotGlyph_Stored. | ||
| PlotGlyph_Byte2 | 25856 | LD B,8 | Eight pixel rows. | |
| PlotGlyph_Shift4 | 25858 | LD A,(DE) | Take one glyph byte and the previous screen byte. | |
| 25859 | DEC HL | |||
| 25860 | SRL (HL) | Make room for four pixels. | ||
| 25862 | SRL (HL) | |||
| 25864 | SRL (HL) | |||
| 25866 | SRL (HL) | |||
| 25868 | SLA A | Shift the first two pixels in. | ||
| 25870 | RL (HL) | |||
| 25872 | SLA A | |||
| 25874 | RL (HL) | |||
| 25876 | SLA A | Shift the other two pixels in. | ||
| 25878 | RL (HL) | |||
| 25880 | SLA A | |||
| 25882 | RL (HL) | |||
| 25884 | INC HL | Store the shifted byte on this pixel row. | ||
| 25885 | LD (HL),A | |||
| 25886 | INC H | The next pixel row. | ||
| 25887 | INC DE | |||
| 25888 | DJNZ PlotGlyph_Shift4 | All eight. | ||
| 25890 | POP HL | This column restores the screen address itself and advances. | ||
| 25891 | JR PlotGlyph_Advance | |||
| PlotGlyph_Byte3 | 25893 | LD B,8 | Eight pixel rows. | |
| PlotGlyph_Top | 25895 | LD A,192 | Keep the top two pixels already on screen. | |
| 25897 | AND (HL) | |||
| 25898 | LD (HL),A | |||
| 25899 | LD A,(DE) | Shift the glyph right by two. | ||
| 25900 | SRL A | |||
| 25902 | SRL A | |||
| 25904 | OR (HL) | OR it into the screen byte. | ||
| 25905 | LD (HL),A | |||
| 25906 | INC H | The next pixel row, then the shared advance. | ||
| 25907 | INC DE | |||
| 25908 | DJNZ PlotGlyph_Top | |||
| 25910 | JR PlotGlyph_Stored | |||
|
The next character moves one column right. Column 41 is the margin, so the cursor wraps.
|
||||
| PlotGlyph_Advance | 25912 | POP AF | Keep the character and read the column. | |
| 25913 | PUSH AF | |||
| 25914 | LD A,(23434) | |||
| 25917 | CP 41 | Column 41 wraps to the next row. | ||
| 25919 | JP Z,PlotCharacter_Newline | |||
| 25922 | INC A | Otherwise the cursor moves one column right. | ||
| 25923 | LD (23434),A | |||
|
This entry point is used by the routine at PlotCharacter.
|
||||
| PlotGlyph_Done | 25926 | POP AF | Restore the registers saved around the glyph from the stack. | |
| 25927 | POP DE | |||
| 25928 | POP BC | |||
| 25929 | POP HL | |||
| 25930 | RET | Return. | ||
| Prev: 25596 | Up: Map | Next: 25931 |