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Routines |
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Finishes the last step of a segment: the end of the segment is stored at offset 02 of the record and DrawEdgePixels draws the pixels at the edge of a sloped segment. If steps of the segment were flagged (FlaggedSteps is not zero) and the horizontal offset is a multiple of eight, the routine starts or stops the horizontal speed in HorizontalSpeed depending on the direction of the segment and fills the pixels of the steps that were flagged with FillStripWithPattern, using the chequer pattern or blank. Purpose not yet known for the details of this.
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| EndSegment | D729 | LD (IX+$02),D | Write D to offset 02 of IX. | |
| D72C | LD SP,$5B7A | Set the stack pointer to 5B7A. | ||
| D72F | CALL DrawEdgePixels | Call DrawEdgePixels. | ||
| D732 | LD A,($5C2F) | The flagged steps. | ||
| D735 | AND A | Jump to FinishSegment if A is zero. | ||
| D736 | JP Z,FinishSegment | |||
| D739 | LD A,($CE41) | The horizontal offset. | ||
| D73C | AND %00000111 | Keep the bits of A that are set in 07. | ||
| D73E | JP NZ,FinishSegment | Jump to FinishSegment if the zero flag is clear. | ||
| D741 | LD ($5C1A),A | The alignment that should stop the scroll. | ||
| D744 | LD A,($CCBB) | The horizontal scroll speed. | ||
| D747 | AND A | Jump to EndSegment_Fill if A is not zero. | ||
| D748 | JP NZ,EndSegment_Fill | |||
| D74B | LD A,($CE37) | The vertical step. | ||
| D74E | AND A | Jump to FinishSegment if A is zero. | ||
| D74F | JP Z,FinishSegment | |||
| D752 | LD ($5C1A),A | The vertical step that should stop the scroll. | ||
| D755 | LD A,($E41B) | The slope direction. | ||
| D758 | LD B,A | B=A. | ||
| D759 | LD A,($CE59) | The horizontal step copy. | ||
| D75C | AND A | Jump to EndSegment_Store if A is zero. | ||
| D75D | JR Z,EndSegment_Store | |||
| D75F | LD A,($5C35) | The upside-down segment flag. | ||
| EndSegment_Store | D762 | XOR B | Flip the bits of A that are set in B. | |
| D763 | LD ($CCBB),A | Update the horizontal scroll speed. | ||
| EndSegment_Fill | D766 | LD A,($CE37) | The vertical step. | |
| D769 | AND A | Jump to FillSlopeEdge if A is zero. | ||
| D76A | JP Z,FillSlopeEdge | |||
| D76D | EXX | Switch to the alternate registers. | ||
| D76E | LD HL,($CE4F) | Fetch the word at SavedScreenAddress into HL. | ||
| D771 | LD A,($CE53) | The saved row. | ||
| D774 | LD ($CE44),A | Update the segment row. | ||
| D777 | LD A,($CE59) | The horizontal step copy. | ||
| D77A | AND A | Jump to EndSegment_Pattern if A is not zero. | ||
| D77B | JR NZ,EndSegment_Pattern | |||
| D77D | LD ($5C35),A | Update the upside-down segment flag. | ||
| D780 | LD A,($E41B) | The slope direction. | ||
| D783 | NEG | Negate A. | ||
| D785 | LD ($CE36),A | Update the column step. | ||
| EndSegment_Pattern | D788 | LD DE,$55AA | DE=55AA. | |
| D78B | LD A,($CCBB) | The horizontal scroll speed. | ||
| D78E | LD B,A | B=A. | ||
| D78F | LD A,($5C35) | The upside-down segment flag. | ||
| D792 | XOR B | Flip the bits of A that are set in B. | ||
| D793 | LD B,A | B=A. | ||
| D794 | LD A,($E41B) | The slope direction. | ||
| D797 | XOR B | Flip the bits of A that are set in B. | ||
| D798 | BIT 7,A | Jump to EndSegment_Direction if bit 7 of A is clear. | ||
| D79A | JR Z,EndSegment_Direction | |||
| D79C | LD DE,$0000 | DE=00. | ||
| EndSegment_Direction | D79F | LD A,($E41B) | The slope direction. | |
| D7A2 | CP $FF | Jump to EndSegment_Flat if A is FF. | ||
| D7A4 | JR Z,EndSegment_Flat | |||
| D7A6 | LD A,($CCBB) | The horizontal scroll speed. | ||
| D7A9 | BIT 7,A | Jump to EndSegment_Column if bit 7 of A is set. | ||
| D7AB | JR NZ,EndSegment_Column | |||
| D7AD | DEC L | Step L back. | ||
| D7AE | JP EndSegment_Rows | Jump to EndSegment_Rows. | ||
| EndSegment_Column | D7B1 | LD A,($5C24) | The column step size. | |
| D7B4 | ADD A,L | A gains L. | ||
| D7B5 | LD L,A | L=A. | ||
| D7B6 | JP EndSegment_Jump | Jump to EndSegment_Jump. | ||
| EndSegment_Flat | D7B9 | LD A,($CCBB) | The horizontal scroll speed. | |
| D7BC | BIT 7,A | Jump to EndSegment_Step if bit 7 of A is set. | ||
| D7BE | JR NZ,EndSegment_Step | |||
| D7C0 | DEC L | Step L back. | ||
| EndSegment_Jump | D7C1 | JP EndSegment_Rows | Jump to EndSegment_Rows. | |
| EndSegment_Step | D7C4 | LD A,($CE36) | The column step. | |
| D7C7 | ADD A,L | A gains L. | ||
| D7C8 | LD L,A | L=A. | ||
| EndSegment_Rows | D7C9 | LD A,($CE59) | The horizontal step copy. | |
| D7CC | AND A | Jump to EndSegment_Strip if A is not zero. | ||
| D7CD | JR NZ,EndSegment_Strip | |||
| D7CF | LD A,($5C2F) | The flagged steps. | ||
| D7D2 | LD B,A | B=A. | ||
| D7D3 | XOR A | Clear A. | ||
| EndSegment_Rows2 | D7D4 | ADD A,$10 | Add 10 to A. | |
| D7D6 | DJNZ EndSegment_Rows2 | Decrease B and jump to EndSegment_Rows2 until none remain. | ||
| D7D8 | LD ($CE5A),A | Update the vertical step copy. | ||
| D7DB | LD A,$01 | A=01. | ||
| D7DD | LD ($5C2F),A | Update the flagged steps. | ||
| EndSegment_Strip | D7E0 | LD A,($CE5A) | The vertical step copy. | |
| D7E3 | SRL A | Shift A right. | ||
| D7E5 | LD C,A | C=A. | ||
| D7E6 | EXX | Switch to the alternate registers. | ||
| D7E7 | LD A,($5C2F) | The flagged steps. | ||
| D7EA | LD B,A | B=A. | ||
| D7EB | CALL FillStripWithPattern | Call FillStripWithPattern. | ||
| D7EE | LD A,($5C1A) | See whether that marker should stop the scroll. | ||
| D7F1 | AND A | Jump to FinishSegment if A is zero. | ||
| D7F2 | JR Z,FinishSegment | |||
| D7F4 | XOR A | Clear A. | ||
| D7F5 | LD ($CCBB),A | Update the horizontal scroll speed. | ||
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Continue on to FinishSegment.
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