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Routines |
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Used by the routine at ScrollWorld.
Used while the world is scrolling in at the start of a life. If the flag at ScrollInFlag is 03 the scroll is finished (see FinishScrollIn). If not, the vertical scroll speed is set to 04. If the flag at ChequeredFloorFlag is zero the scroll lasts for the number of steps that are left in B. Otherwise it looks at the six bytes of the screen where the ship is, and at the row above them, and goes on scrolling until they are all blank. Then the flag is set to 03, the playfield is coloured and the tiles are made again.
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| LookForGround | DD79 | LD A,($5C3C) | The scroll-in flag. | |
| DD7C | CP $03 | Jump to FinishScrollIn if A is 03. | ||
| DD7E | JP Z,FinishScrollIn | |||
| DD81 | LD A,$04 | A=04. | ||
| DD83 | LD ($CCBA),A | Update the vertical scroll speed. | ||
| DD86 | LD A,($DDF2) | The chequered floor flag. | ||
| DD89 | AND A | Jump to LookForGround_Count if A is zero. | ||
| DD8A | JR Z,LookForGround_Count | |||
| DD8C | LD B,$06 | B=06. | ||
| DD8E | LD HL,($C902) | Fetch the word at C902 into HL. | ||
| DD91 | CALL GetScreenAddress | Call GetScreenAddress. | ||
| LookForGround_Loop | DD94 | LD A,(HL) | Read HL. | |
| DD95 | AND A | Jump to LookForGround_Restore if A is not zero. | ||
| DD96 | JR NZ,LookForGround_Restore | |||
| DD98 | DEC H | Step H back. | ||
| DD99 | LD A,(HL) | Read HL. | ||
| DD9A | AND A | Jump to LookForGround_Restore if A is not zero. | ||
| DD9B | JR NZ,LookForGround_Restore | |||
| DD9D | INC H | Advance H. | ||
| DD9E | INC L | Advance L. | ||
| DD9F | DJNZ LookForGround_Loop | Decrease B and jump to LookForGround_Loop until none remain. | ||
| DDA1 | POP BC | Bring BC back off the stack. | ||
| DDA2 | JR LookForGround_Found | Jump to LookForGround_Found. | ||
| LookForGround_Restore | DDA4 | POP BC | Bring BC back off the stack. | |
| DDA5 | JR ScrollInWorld | Jump to ScrollInWorld. | ||
| LookForGround_Count | DDA7 | POP BC | Bring BC back off the stack. | |
| DDA8 | DJNZ ScrollInWorld | Decrease B and jump to ScrollInWorld until none remain. | ||
| LookForGround_Found | DDAA | CALL ColourPlayfield | Call ColourPlayfield. | |
| DDAD | XOR A | Clear A. | ||
| DDAE | LD ($CCBA),A | Update the vertical scroll speed. | ||
| DDB1 | LD A,$03 | A=03. | ||
| DDB3 | LD ($5C3C),A | Update the scroll-in flag. | ||
| DDB6 | LD HL,($CE57) | Fetch the word at MapPosition into HL. | ||
| DDB9 | CALL MakeTiles | Call MakeTiles. | ||
| DDBC | JP ScrollInWorld | Jump to ScrollInWorld. | ||
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