Routines
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50413: Draw Ship Top
Used by the routines at UpdateCrystalStack and ExplodeShip.
Draws the top of the ship, which is one of the six sprites for types 1 to 6: the one that is used depends on the horizontal speed of the ship, and type 6 is used while the ship has just been hit. Then it checks for the pause keys with CheckPauseAndSilence and fires the weapons with FireWeapons. Carries on with DrawMainFlame or DrawSideFlames on alternate frames. This is a best reading of the code.
DrawShipTop 50413 LD HL,0 HL=0.
50416 LD (23580),HL No saved row count.
50419 LD IX,51132 The ship top object.
50423 CALL FetchObjectFrameTable Call FetchObjectFrameTable.
50426 LD HL,(51133) Fetch the word at 51133 into HL.
50429 LD (49027),HL The position of the ship top.
50432 CALL ReadSpriteSize Call ReadSpriteSize.
50435 CALL SetFirstRowGroup Call SetFirstRowGroup.
50438 LD HL,(49027) Fetch the word at 49027 into HL.
50441 CALL GetScreenAddress Call GetScreenAddress.
50444 LD IY,42567 The sixth aligned-row erase.
50448 CALL TestDirection Call TestDirection.
50451 JR NZ,DrawShipTop_Frame Jump to DrawShipTop_Frame if the zero flag is clear.
50453 LD IY,42956 The sixth mirrored-row erase.
DrawShipTop_Frame 50457 EXX Switch to the alternate registers.
50458 LD E,(IX+0) Read offset 0 of IX into E.
50461 LD A,(51460) The item the ship is about to pick up.
50464 AND A Jump to DrawShipTop_Speed if A is zero.
50465 JR Z,DrawShipTop_Speed
50467 LD A,(23608) The ship row.
50470 SUB 9 Subtract 9 from A.
50472 LD (51134),A The row of the carried item.
50475 LD (49028),A The row the item is drawn on.
50478 LD E,255 E=255.
50480 XOR A Clear A.
50481 LD (51460),A Update the item the ship is about to pick up.
DrawShipTop_Speed 50484 LD HL,(51454) Fetch the word at 51454 into HL.
50487 LD A,H A=H.
50488 LD H,L H=L.
50489 LD L,A L=A.
50490 LD A,H A=H.
50491 AND A Jump to DrawShipTop_Fast if A is not zero.
50492 JR NZ,DrawShipTop_Fast
50494 LD A,L A=L.
50495 CP 128 Compare A with 128.
50497 LD A,H A=H.
50498 JR NC,DrawShipTop_Fast Jump to DrawShipTop_Fast if the carry flag is clear.
50500 LD A,128 A=128.
50502 LD (51135),A The ship top faces left.
50505 JR DrawShipTop_Select Jump to DrawShipTop_Select.
DrawShipTop_Fast 50507 AND %10000000 Keep the bits of A that are set in 128.
50509 LD (51135),A The facing of the ship top.
50512 CALL NZ,NegateNumber Call NegateNumber if the zero flag is clear.
DrawShipTop_Select 50515 LD A,L A=L.
50516 AND %10000000 Keep the bits of A that are set in 128.
50518 RLCA Rotate A left.
50519 SLA H Shift H left.
50521 ADD A,H A gains H.
50522 INC A Advance A.
50523 LD (IX+0),A Write A to offset 0 of IX.
50526 LD A,(23614) The horizontal scroll limit.
50529 LD B,A B=A.
50530 LD A,H A=H.
50531 CP B Jump to DrawShipTop_Hit if A is less than B.
50532 JR C,DrawShipTop_Hit
50534 INC B Advance B.
50535 LD (IX+0),B Write B to offset 0 of IX.
DrawShipTop_Hit 50538 LD A,(36691) The ship state.
50541 AND A Jump to DrawShipTop_Show if A is not zero.
50542 JR NZ,DrawShipTop_Show
50544 LD A,(51137) The hit-flash timer.
50547 AND A Jump to DrawShipTop_Show if A is zero.
50548 JR Z,DrawShipTop_Show
50550 DEC A Step A back.
50551 LD (51137),A Update the hit-flash timer.
50554 LD (IX+0),6 Store 6 at offset 0 of IX.
50558 JR DrawShipTop_Position Jump to DrawShipTop_Position.
DrawShipTop_Show 50560 LD A,(36691) The ship state.
50563 CP 10 Jump to DrawShipTop_Draw if A is 10 or more.
50565 JR NC,DrawShipTop_Draw
50567 LD A,(53436) The collision kind.
50570 AND A Jump to DrawShipTop_Position if A is not zero.
50571 JR NZ,DrawShipTop_Position
50573 LD A,(IX+0) Read offset 0 of IX.
50576 CP E Jump to DrawShipTop_Position if A is not E.
50577 JR NZ,DrawShipTop_Position
50579 LD A,(51136) The turn flag.
50582 AND A Jump to DrawShipTop_Position if A is not zero.
50583 JR NZ,DrawShipTop_Position
50585 LD (23580),A The ship is not turning.
DrawShipTop_Position 50588 CALL FetchObjectFrameTable Call FetchObjectFrameTable.
50591 LD B,104 B=104.
50593 LD A,(51453) The ship's facing.
50596 BIT 7,A Jump to DrawShipTop_Store if bit 7 of A is clear.
50598 JR Z,DrawShipTop_Store
50600 LD B,120 B=120.
DrawShipTop_Store 50602 LD A,B A=B.
50603 LD (51133),A The column of the ship top.
50606 LD (49027),A The column of the ship top.
50609 CALL FetchObjectFrameTable Call FetchObjectFrameTable.
50612 CALL ReadSpriteSize Call ReadSpriteSize.
50615 CALL SetSecondRowGroup Call SetSecondRowGroup.
50618 LD IX,42641 The sixth aligned-row draw.
50622 CALL TestDirection Call TestDirection.
50625 JR NZ,DrawShipTop_Draw Jump to DrawShipTop_Draw if the zero flag is clear.
50627 LD IX,43001 The sixth mirrored-row draw.
50631 LD A,(49027) The column of the ship top.
50634 ADD A,8 Add 8 to A.
50636 LD (49027),A The column one byte to the right.
DrawShipTop_Draw 50639 CALL DrawSpritesDirectly Call DrawSpritesDirectly.
50642 XOR A Clear A.
50643 LD (53436),A Update the collision kind.
50646 LD A,(51132) The ship top object.
50649 CP 6 Jump to DrawShipTop_Pause if A is 6.
50651 JP Z,DrawShipTop_Pause
50654 LD HL,(49027) Fetch the word at 49027 into HL.
50657 LD A,H A=H.
50658 SUB 7 Subtract 7 from A.
50660 LD H,A H=A.
50661 CALL AttributeAddress Call AttributeAddress.
50664 LD (HL),71 Store 71 at the address in HL.
This entry point is used by the routine at RunFrame.
DrawShipTop_Pause 50666 CALL CheckPauseAndSilence Call CheckPauseAndSilence.
50669 CALL FireWeapons Call FireWeapons.
50672 LD A,(36691) The ship state.
50675 CP 10 Jump to DrawSideFlames if A is 10 or more.
50677 JR NC,DrawSideFlames
50679 LD A,(39524) The frame counter.
50682 AND %00000001 Keep the bits of A that are set in 1.
50684 JP Z,DrawMainFlame Jump to DrawMainFlame if the zero flag is set.
Continue on to DrawSideFlames.
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