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Routines |
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The parameters for block drawing start at the byte after the address in IX. These are:
The block data is comprised of one or more byte values.
If a block data byte has its most significant bit reset, then it is interpreted as a block style index corresponding to an entry in the table of block style definitions at 49794, and a single such block is drawn before the next byte is processed.
If a block data byte has its most significant bit set, then bits 0-6 are interpreted as a run-length (e.g. a value of 144 means a run-length of 16 2 × 2 blocks) and the following data byte represents the index of the entry in the table of block style definitions at 49794 to repeatedly use throughout the run. Once the run of blocks has been drawn, the next byte is processed.
When the value 255, the end marker, is encountered, the vertical drawing ends.
Used by the routine at 39047.
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| 39291 | INC IX | Advance IX to x-coordinate... | ||||||||||||||||||
| 39293 | LD L,(IX+0) | ...and load into L | ||||||||||||||||||
| 39296 | INC IX | Advance IX to y-coordinate... | ||||||||||||||||||
| 39298 | LD H,(IX+0) | ...and load into H | ||||||||||||||||||
| 39301 | INC IX | Advance IX to first block layout data byte | ||||||||||||||||||
| 39303 | LD (23463),HL | Store coordinates of top-left of block at 23463 | ||||||||||||||||||
| 39306 | LD A,(IX+0) | Load A with next block layout data... | ||||||||||||||||||
| 39309 | CP 255 | ...and if this is 255 (end marker)... | ||||||||||||||||||
| 39311 | JR Z,39332 | ...then skip ahead to 39332 | ||||||||||||||||||
| 39313 | BIT 7,A | If draw-run flag is set... | ||||||||||||||||||
| 39315 | JR NZ,39337 | ...then skip ahead to 39337 | ||||||||||||||||||
| 39317 | CALL 39366 | Draw 2 × 2 block with style index A at coordinates stored at 23463 then move right two characters | ||||||||||||||||||
| 39320 | INC IX | Advance IX to next block layout data | ||||||||||||||||||
| 39322 | LD HL,(23463) | Load HL with coordinates of top-left of block just drawn... | ||||||||||||||||||
| 39325 | INC H | ...add two to y-coordinate... | ||||||||||||||||||
| 39326 | INC H | ... | ||||||||||||||||||
| 39327 | LD (23463),HL | ...and store updated coordinates at 23463 | ||||||||||||||||||
| 39330 | JR 39306 | Loop back to 39306 to process next block layout data | ||||||||||||||||||
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End marker encountered
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| 39332 | INC IX | Advance IX to next byte in room layout data... | ||||||||||||||||||
| 39334 | JP 39067 | ...and jump to 39067 to process | ||||||||||||||||||
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Draw-run flag set
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| 39337 | AND 127 | Reset draw-run flag... | ||||||||||||||||||
| 39339 | LD B,A | ...and load B with run length | ||||||||||||||||||
| 39340 | INC IX | Advance IX to block style index... | ||||||||||||||||||
| 39342 | LD A,(IX+0) | ...and load into A | ||||||||||||||||||
| 39345 | INC IX | Advance IX to next block layout data | ||||||||||||||||||
| 39347 | PUSH BC | Store BC (B = remaining number of blocks to draw) | ||||||||||||||||||
| 39348 | PUSH AF | Store AF | ||||||||||||||||||
| 39349 | CALL 39366 | Draw 2 × 2 block with style index A at coordinates stored at 23463 then move right two characters | ||||||||||||||||||
| 39352 | LD HL,(23463) | Load HL with coordinates of top-left of block just drawn... | ||||||||||||||||||
| 39355 | INC H | ...add two to y-coordinate... | ||||||||||||||||||
| 39356 | INC H | ... | ||||||||||||||||||
| 39357 | LD (23463),HL | ...and store updated coordinates at 23463 | ||||||||||||||||||
| 39360 | POP AF | Restore AF | ||||||||||||||||||
| 39361 | POP BC | Restore BC (B = remaining number of blocks to draw) | ||||||||||||||||||
| 39362 | DJNZ 39347 | Decrease remaining number of blocks and loop back to 39347 if not zero | ||||||||||||||||||
| 39364 | JR 39306 | Loop back to 39306 for next block layout data | ||||||||||||||||||
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