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Routines |
| Prev: B414 | Up: Map | Next: B5B5 |
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Used by the routine at UpdateShots.
Updates one of the shots that the ship has fired. Shots that have bit 7 of offset 15 set go to UpdateSpecialShot. A shot that is starting (with a length of zero at offset 0E) is given a starting vertical position from ShipRow with a random step, and a random colour. Shots that are facing right continue at UpdateShot_Right and ones that are facing left at UpdateLeftShot.
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| UpdateShot | B483 | LD A,($C8EC) | The high byte of the ship's horizontal speed. | |||||
| B486 | LD (IX+$07),A | Write the high byte of the horizontal speed. | ||||||
| B489 | LD A,$80 | A=80. | ||||||
| B48B | LD ($5C25),A | The shot stops on the terrain. | ||||||
| B48E | BIT 7,(IX+$15) | Jump to UpdateSpecialShot if bit 7 of offset 15 of IX is set. | ||||||
| B492 | JP NZ,UpdateSpecialShot | |||||||
| B495 | LD A,$01 | A=01. | ||||||
| B497 | LD ($A1D7),A | One row to erase. | ||||||
| B49A | LD ($A1D8),A | One row to draw. | ||||||
| B49D | LD A,(IX+$0E) | The high byte of the vertical acceleration. | ||||||
| B4A0 | AND A | Jump to UpdateShot_Right if A is not zero. | ||||||
| B4A1 | JR NZ,UpdateShot_Right | |||||||
| B4A3 | LD (IX+$10),$00 | Store 00 at offset 10 of IX. | ||||||
| B4A7 | LD (IX+$07),$00 | Store 00 at offset 07 of IX. | ||||||
| B4AB | CALL ChooseRandomStep | Call ChooseRandomStep. | ||||||
| B4AE | LD A,($CCBA) | The vertical scroll speed. | ||||||
| B4B1 | NEG | Negate A. | ||||||
| B4B3 | ADD A,B | A gains B. | ||||||
| B4B4 | LD (IX+$09),B | Write the high byte of the vertical speed. | ||||||
| B4B7 | LD B,A | B=A. | ||||||
| B4B8 | LD A,($5C38) | The ship row. | ||||||
| B4BB | ADD A,B | A gains B. | ||||||
| B4BC | LD (IX+$0C),A | Write the low byte of the horizontal acceleration. | ||||||
| B4BF | CALL ChooseRandomColour | Call ChooseRandomColour. | ||||||
| B4C2 | CALL MoveObject | Call MoveObject. | ||||||
| B4C5 | LD (IX+$09),$00 | Store 00 at offset 09 of IX. | ||||||
| UpdateShot_Right | B4C9 | BIT 7,(IX+$00) | Jump to UpdateLeftShot if bit 7 of offset 00 of IX is set. | |||||
| B4CD | JP NZ,UpdateLeftShot | |||||||
| B4D0 | LD DE,$B3DA | The shot offsets. | ||||||
| B4D3 | CALL AddShotOffset | Call AddShotOffset. | ||||||
| B4D6 | CALL FindObjectScreenAddress | Call FindObjectScreenAddress. | ||||||
| B4D9 | LD B,(IX+$0E) | The high byte of the vertical acceleration. | ||||||
| B4DC | EXX | Switch to the alternate registers. | ||||||
| B4DD | BIT 7,(IX+$10) | Jump to UpdateShot_Hit if bit 7 of offset 10 of IX is set. | ||||||
| B4E1 | JR NZ,UpdateShot_Hit | |||||||
| B4E3 | LD A,(IX+$0E) | The high byte of the vertical acceleration. | ||||||
| B4E6 | AND A | Jump to UpdateShot_Longer if A is not zero. | ||||||
| B4E7 | JR NZ,UpdateShot_Longer | |||||||
| B4E9 | LD (IX+$0F),$08 | Store 08 at offset 0F of IX. | ||||||
| B4ED | LD (IX+$0B),$88 | Store 88 at offset 0B of IX. | ||||||
| UpdateShot_Longer | B4F1 | LD A,$10 | A=10. | |||||
| B4F3 | ADD A,(IX+$07) | Add the byte at offset 07 of IX to A. | ||||||
| B4F6 | LD (IX+$07),A | Write the high byte of the horizontal speed. | ||||||
| B4F9 | CALL TestShotHitsGround | Call TestShotHitsGround. | ||||||
| B4FC | JR Z,UpdateShot_Move | Jump to UpdateShot_Move if the zero flag is set. | ||||||
| B4FE | LD A,$F0 | A=F0. | ||||||
| B500 | ADD A,(IX+$07) | Add the byte at offset 07 of IX to A. | ||||||
| B503 | LD (IX+$07),A | Write the high byte of the horizontal speed. | ||||||
| B506 | SET 7,(IX+$10) | Set bit 7 of offset 10 of IX. | ||||||
| B50A | SET 5,(IX+$10) | Set bit 5 of offset 10 of IX. | ||||||
| B50E | JP UpdateShot_Count | Jump to UpdateShot_Count. | ||||||
| UpdateShot_Move | B511 | LD A,$08 | A=08. | |||||
| B513 | ADD A,(IX+$0B) | Add the byte at offset 0B of IX to A. | ||||||
| B516 | LD (IX+$0B),A | Write the high byte of the horizontal acceleration. | ||||||
| B519 | CP $B8 | Jump to UpdateShot_Length if A is not B8. | ||||||
| B51B | JR NZ,UpdateShot_Length | |||||||
| B51D | SET 7,(IX+$10) | Set bit 7 of offset 10 of IX. | ||||||
| UpdateShot_Length | B521 | LD A,(IX+$0E) | The high byte of the vertical acceleration. | |||||
| B524 | INC A | Advance A. | ||||||
| B525 | LD (IX+$0E),A | Write the high byte of the vertical acceleration. | ||||||
| B528 | LD A,(IX+$0F) | The low byte of the vertical acceleration. | ||||||
| B52B | DEC A | Step A back. | ||||||
| B52C | LD (IX+$0F),A | Write the low byte of the vertical acceleration. | ||||||
| B52F | JP UpdateShot_Table | Jump to UpdateShot_Table. | ||||||
| UpdateShot_Hit | B532 | BIT 5,(IX+$10) | Jump to UpdateShot_Stopped if bit 5 of offset 10 of IX is set. | |||||
| B536 | JR NZ,UpdateShot_Stopped | |||||||
| B538 | CALL TestShotHitsGround | Call TestShotHitsGround. | ||||||
| B53B | JR Z,UpdateShot_Facing | Jump to UpdateShot_Facing if the zero flag is set. | ||||||
| B53D | SET 5,(IX+$10) | Set bit 5 of offset 10 of IX. | ||||||
| UpdateShot_Stopped | B541 | LD A,(IX+$07) | The high byte of the horizontal speed. | |||||
| B544 | NEG | Negate A. | ||||||
| B546 | ADD A,(IX+$0B) | Add the byte at offset 0B of IX to A. | ||||||
| B549 | LD (IX+$0B),A | Write the high byte of the horizontal acceleration. | ||||||
| B54C | LD (IX+$07),$00 | Store 00 at offset 07 of IX. | ||||||
| B550 | BIT 6,(IX+$10) | Test bit 6 of offset 10 of IX. | ||||||
| B554 | LD B,(IX+$0E) | The high byte of the vertical acceleration. | ||||||
| B557 | LD C,(IX+$0B) | The high byte of the horizontal acceleration. | ||||||
| B55A | JR Z,UpdateShot_Clip | Jump to UpdateShot_Clip if the zero flag is set. | ||||||
| B55C | DEC B | Step B back. | ||||||
| B55D | LD A,C | A=C. | ||||||
| B55E | ADD A,$08 | Add 08 to A. | ||||||
| B560 | LD C,A | C=A. | ||||||
| UpdateShot_Clip | B561 | SLA B | Shift B left. | |||||
| B563 | SLA B | Shift B left. | ||||||
| B565 | SLA B | Shift B left. | ||||||
| B567 | LD A,B | A=B. | ||||||
| B568 | ADD A,C | A gains C. | ||||||
| B569 | AND %11111000 | Keep the bits of A that are set in F8. | ||||||
| B56B | CP $E4 | Jump to UpdateShot_Facing if A is less than E4. | ||||||
| B56D | JR C,UpdateShot_Facing | |||||||
| B56F | CP $F0 | Jump to UpdateShot_Shorten if A is less than F0. | ||||||
| B571 | JR C,UpdateShot_Shorten | |||||||
| B573 | LD (IX+$0E),$00 | Store 00 at offset 0E of IX. | ||||||
| UpdateShot_Shorten | B577 | LD A,(IX+$0E) | The high byte of the vertical acceleration. | |||||
| B57A | DEC A | Step A back. | ||||||
| B57B | LD (IX+$0E),A | Write the high byte of the vertical acceleration. | ||||||
| B57E | LD A,(IX+$0B) | The high byte of the horizontal acceleration. | ||||||
| B581 | SUB $08 | Subtract 08 from A. | ||||||
| B583 | LD (IX+$0B),A | Write the high byte of the horizontal acceleration. | ||||||
| UpdateShot_Facing | B586 | BIT 6,(IX+$10) | Jump to UpdateShot_Count if bit 6 of offset 10 of IX is clear. | |||||
| B58A | JR Z,UpdateShot_Count | |||||||
| B58C | LD A,(IX+$0E) | The high byte of the vertical acceleration. | ||||||
| B58F | DEC A | Step A back. | ||||||
| B590 | LD (IX+$0E),A | Write the high byte of the vertical acceleration. | ||||||
| B593 | LD A,(IX+$0B) | The high byte of the horizontal acceleration. | ||||||
| B596 | ADD A,$08 | Add 08 to A. | ||||||
| B598 | LD (IX+$0B),A | Write the high byte of the horizontal acceleration. | ||||||
| B59B | JR UpdateShot_Table | Jump to UpdateShot_Table. | ||||||
| UpdateShot_Count | B59D | LD A,(IX+$0F) | The low byte of the vertical acceleration. | |||||
| B5A0 | DEC A | Step A back. | ||||||
| B5A1 | LD (IX+$0F),A | Write the low byte of the vertical acceleration. | ||||||
| B5A4 | JR NZ,UpdateShot_Table | Jump to UpdateShot_Table if the zero flag is clear. | ||||||
| B5A6 | SET 6,(IX+$10) | Set bit 6 of offset 10 of IX. | ||||||
| UpdateShot_Table | B5AA | LD DE,$B3DA | The shot offsets. | |||||
| B5AD | JR UpdateShot_Offset | Jump to UpdateShot_Offset. | ||||||
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This entry point is used by the routine at UpdateLeftShot.
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| UpdateShot_LeftTable | B5AF | LD DE,$B3E2 | The second shot offset. | |||||
| UpdateShot_Offset | B5B2 | CALL AddShotOffset | Call AddShotOffset. | |||||
| Prev: B414 | Up: Map | Next: B5B5 |