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Routines |
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Used by the routines at TestBlockRow_Draw and DrawBlockSection.
Draws the bytes of a row of a block into the screen buffer. A column below 16 is off the view, and a column of 192 is drawn only when bits 1-2 of DrawingFlags are clear. The tile is read through the stack. Those bits clear draw the bytes plain, with 50705; otherwise DrawShiftedRows_Two shifts them.
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| DrawBlockBytes | 51053 | CP 16 | A column below 16 is off the view. | |||||||
| 51055 | RET C | |||||||||
| 51056 | LD C,A | Keep the column. | ||||||||
| 51057 | CP 192 | A column of 192 needs the drawing flags. | ||||||||
| 51059 | JR NZ,DrawBlockBytes_Return | |||||||||
| 51061 | LD A,(23792) | Read the drawing flags. | ||||||||
| 51064 | AND %00000110 | Use bits 1-2 of the drawing flags. | ||||||||
| 51066 | JR Z,DrawBlockBytes_Offset | Draw when those bits are clear. | ||||||||
| DrawBlockBytes_Return | 51068 | RET NC | Leave a shifted column of 192 undrawn. | |||||||
| DrawBlockBytes_Offset | 51069 | SRL C | The byte offset is the column divided by eight. | |||||||
| 51071 | SRL C | |||||||||
| 51073 | SRL C | |||||||||
| 51075 | LD (23770),SP | Remember the stack pointer. | ||||||||
| 51079 | LD SP,HL | Read the tile through the stack. | ||||||||
| 51080 | LD HL,(23739) | Fetch the strip address. | ||||||||
| 51083 | LD B,0 | Add the byte offset to the strip. | ||||||||
| 51085 | ADD HL,BC | |||||||||
| 51086 | LD A,(23792) | Read the drawing flags again. | ||||||||
| 51089 | AND %00000110 | Use bits 1-2 of the drawing flags. | ||||||||
| 51091 | LD B,8 | Draw the plain bytes when those bits are clear. | ||||||||
| 51093 | JP Z,DrawBlockRow_Loop | |||||||||
| 51096 | EX DE,HL | Keep the strip address aside. | ||||||||
| 51097 | ADD A,248 | The shift selects the page of the shifted rows. | ||||||||
| 51099 | LD HL,46344 | Use the two-byte shifted rows. | ||||||||
| 51102 | LD (46388),HL | Give that routine to the shifted drawer. | ||||||||
| 51105 | LD (46393),HL | |||||||||
| 51108 | LD H,A | Keep the page. | ||||||||
| 51109 | LD A,8 | The shifted row count is 8. | ||||||||
| 51111 | EX AF,AF' | |||||||||
| 51112 | LD A,(DE) | Read the first screen byte. | ||||||||
| 51113 | JP DrawShiftedRows_Two | Draw the shifted rows. | ||||||||
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