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Routines |
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Used by the routines at DrawingSetup and Drawing_PlotTheSelectedPixel.
Turns the pixel coordinate into a screen address and sets the bit in that screen byte.
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| Drawing_AddressThePixel | 33205 | PUSH HL | Call Drawing_ScreenAddressFromTheRow to turn the pen into a screen address. | |
| 33206 | CALL Drawing_ScreenAddressFromTheRow | |||
| 33209 | PUSH AF | Keep the screen address and split out its row bits. | ||
| 33210 | PUSH HL | |||
| 33211 | LD A,H | |||
| 33212 | AND %00011000 | Move the row bits of the screen address into the attribute address. | ||
| 33214 | RRCA | Rotate right. | ||
| 33215 | RRCA | Rotate right. | ||
| 33216 | RRCA | Rotate right. | ||
| 33217 | ADD A,88 | Add it on. | ||
| 33219 | LD H,A | Point H at that attribute. | ||
| 33220 | LD A,(HL) | Read the attribute byte. | ||
| 33221 | AND %00111000 | Keep only the paper bits (3-5) of this attribute, and jump to Drawing_AddressThePixel_RestoreTheInkBits unless they match the colour in 33358 shifted into bits 3-5. | ||
| 33223 | LD (HL),A | |||
| 33224 | LD A,(33358) | |||
| 33227 | RLCA | |||
| 33228 | RLCA | |||
| 33229 | RLCA | |||
| 33230 | CP (HL) | |||
| 33231 | JR NZ,Drawing_AddressThePixel_RestoreTheInkBits | |||
| 33233 | XOR 56 | Flip the bits selected by 56. | ||
| Drawing_AddressThePixel_RestoreTheInkBits | 33235 | RRCA | Shift the replacement ink back into the ink bits. | |
| 33236 | RRCA | |||
| 33237 | RRCA | |||
| 33238 | OR (HL) | Combine it with the attribute on screen. | ||
| 33239 | LD (HL),A | Store the attribute. | ||
| 33240 | POP HL | Plot the pixel into the screen byte. | ||
| 33241 | POP AF | |||
| 33242 | OR (HL) | |||
| 33243 | LD (HL),A | Store the screen byte. | ||
| 33244 | POP HL | Restore HL from the stack. | ||
| 33245 | RET | Return. | ||
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View the equivalent code in;
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