Routines
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38670: Handler: Mr Magnetic Brella
Count the alien and steer it toward the scroll position at Jetman_Position. When it is close to the object at World_Slot_1_Position, it picks that object up and carries it.
Input
IX Actor slot
Handler_MrMagneticBrella 38670 LD HL,24158 HL=AlienCount.
38673 INC (HL) Increase AlienCount by one.
38674 BIT 0,(IX+8) Jump to Handler_MrMagneticBrella_AttachedFly if the alien is already attached.
38678 JP NZ,Handler_MrMagneticBrella_AttachedFly
Attach when the alien is close to World_Slot_1_Position.
38681 LD A,(24752) Jump to Handler_MrMagneticBrella_CopyBeside if World_Slot_1_Flags is already set.
38684 AND A
38685 JR NZ,Handler_MrMagneticBrella_CopyBeside
Test whether the alien is horizontally close to the object.
38687 LD H,(IX+3) Fetch the high byte of the world X.
38690 LD L,(IX+2) Fetch the low byte of the world X.
38693 LD DE,(24746) Fetch World_Slot_1_Position.
38697 LD BC,8 Add an 8 tolerance.
38700 ADD HL,BC
38701 SBC HL,DE Subtract the target position.
38703 LD A,H Fetch the high byte of the gap.
38704 AND %00011111 Keep only bits 0-4.
38706 JR NZ,Handler_MrMagneticBrella_CopyBeside Jump to Handler_MrMagneticBrella_CopyBeside if they are not on the same screen.
38708 LD A,L Fetch the low byte of the gap.
38709 CP 16 Jump to Handler_MrMagneticBrella_CopyBeside if it is at least 16.
38711 JR NC,Handler_MrMagneticBrella_CopyBeside
Test whether the alien is vertically close to the object.
38713 LD A,(24748) Fetch World_Slot_1_Y.
38716 SUB (IX+4) Subtract the alien's Y position.
38719 CP 16 Jump to Handler_MrMagneticBrella_CopyBeside if the Y gap is at least 16.
38721 JR NC,Handler_MrMagneticBrella_CopyBeside
Flag both the alien and the object as attached.
38723 SET 0,(IX+8) Set bit 0 of the actor flags.
38727 LD HL,24752 HL=World_Slot_1_Flags.
38730 SET 0,(HL) Set bit 0 of the target flags.
Copy the position at World_Slot_1_Position to the alien if it is beside World_Slot_2_Position.
Handler_MrMagneticBrella_CopyBeside 38732 CALL TestAlienBesideSlot Jump to Handler_MrMagneticBrella_ApplyDownThrust if the alien is not beside World_Slot_2_Position.
38735 JR NZ,Handler_MrMagneticBrella_ApplyDownThrust
38737 LD DE,(24746) Fetch World_Slot_1_Position.
38741 LD (IX+3),D Copy that position into the alien's world X.
38744 LD (IX+2),E
38747 LD A,(24748) Fetch World_Slot_1_Y.
38750 LD (IX+4),A Copy it to the alien's Y position.
Apply downward thrust and update the Y position.
Handler_MrMagneticBrella_ApplyDownThrust 38753 LD A,(IX+6) Jump to Handler_MrMagneticBrella_AddThrust if the vertical thrust is negative.
38756 AND A
38757 JP M,Handler_MrMagneticBrella_AddThrust
38760 CP 48 Jump to Handler_MrMagneticBrella_AddThrustToY if the thrust is already at least 48.
38762 JR NC,Handler_MrMagneticBrella_AddThrustToY
Handler_MrMagneticBrella_AddThrust 38764 ADD A,2 Add 2 to the thrust.
38766 LD (IX+6),A Write the thrust back.
Handler_MrMagneticBrella_AddThrustToY 38769 SRA A Divide the thrust by 16.
38771 SRA A
38773 SRA A
38775 SRA A
38777 ADD A,(IX+4) Add it to the alien's Y position.
38780 CP 176 Jump to Handler_MrMagneticBrella_BounceGround if the alien has hit the ground line.
38782 JR NC,Handler_MrMagneticBrella_BounceGround
Handler_MrMagneticBrella_WriteY 38784 LD (IX+4),A Write the Y position back.
Steer toward the scroll, then animate.
Handler_MrMagneticBrella_Loop 38787 LD H,(IX+3) Fetch the high byte of the world X.
38790 LD L,(IX+2) Fetch the low byte of the world X.
38793 PUSH HL Stash the world X on the stack.
38794 LD DE,(24698) Fetch Jetman_Position.
38798 SBC HL,DE Subtract the scroll position.
38800 LD C,0 C=0.
Leave the speed unchanged if the alien is on this screen or just off its left edge.
38802 LD A,H Fetch the high byte of the gap.
38803 AND %00011111 Keep only bits 0-4.
38805 JR Z,Handler_MrMagneticBrella_RestoreX Jump to Handler_MrMagneticBrella_RestoreX if the alien is on this screen.
38807 OR %11100000 Set bits 5-7.
38809 CPL Flip the bits.
38810 AND A Jump to Handler_MrMagneticBrella_RestoreX if the result is zero.
38811 JR Z,Handler_MrMagneticBrella_RestoreX
38813 BIT 4,H Test bit 4 of the gap.
48 is a signed +48 rightward speed; 208 is signed -48 leftward.
38815 LD A,48 A=48.
38817 JR NZ,Handler_MrMagneticBrella_WriteSpeed Jump to Handler_MrMagneticBrella_WriteSpeed if the alien is left of the scroll.
38819 LD A,208 A=208.
Handler_MrMagneticBrella_WriteSpeed 38821 LD (IX+5),A Write the speed to *IX+5.
Move the carried object with the alien if it is attached.
Handler_MrMagneticBrella_RestoreX 38824 POP HL Restore the world X from the stack.
38825 BIT 0,(IX+8) Jump to Handler_MrMagneticBrella_TickAnimation if the alien is not attached.
38829 JP Z,Handler_MrMagneticBrella_TickAnimation
38832 LD (24746),HL Write the world X back to World_Slot_1_Position.
38835 LD A,(IX+4) Fetch the alien's Y position.
38838 ADD A,26 Add 26.
38840 CP 176 Jump to Handler_MrMagneticBrella_WriteLinkedY if it is still above the ground line.
38842 JR C,Handler_MrMagneticBrella_WriteLinkedY
175 is the ground line.
38844 LD A,175 A=175.
Handler_MrMagneticBrella_WriteLinkedY 38846 LD (24748),A Write it to World_Slot_1_Y.
Animate the alien and set its colour.
Handler_MrMagneticBrella_TickAnimation 38849 INC (IX+17) Increase the animation timer.
38852 LD A,(IX+17) Fetch the animation timer.
38855 AND %00000111 Keep only bits 0-2.
Sprite IDs begin at 64 ("Mr Magnetic Brella: Frame 1").
38857 ADD A,64 Add 64 for the seeking frames.
38859 LD (IX+0),A Write it to the actor type.
38862 BIT 0,(IX+16) Jump to Handler_MrMagneticBrella_SetColour if bit 0 of *IX+16 is reset.
38866 JR Z,Handler_MrMagneticBrella_SetColour
38868 BIT 0,(IX+8) Jump to Handler_MrMagneticBrella_SetColour if the alien is not attached.
38872 JR Z,Handler_MrMagneticBrella_SetColour
38874 LD A,128 Write 128 to World_Slot_1_Flags.
38876 LD (24752),A
Handler_MrMagneticBrella_SetColour 38879 LD (IX+7),69 Write INK:CYAN, PAPER:BLACK (BRIGHT) to the actor colour.
38883 JP PlaceSpawnedAlien_Age Jump to PlaceSpawnedAlien_Age.
Bounce off the ground line.
Handler_MrMagneticBrella_BounceGround 38886 LD A,(IX+6) Jump to Handler_MrMagneticBrella_WriteY if the vertical thrust is negative.
38889 AND A
38890 JP M,Handler_MrMagneticBrella_WriteY
38893 NEG Negate the thrust.
38895 LD (IX+6),A Write it back.
38898 JR Handler_MrMagneticBrella_Loop Jump to Handler_MrMagneticBrella_Loop.
When attached, keep flying and copy the new position back to World_Slot_1_Position.
Handler_MrMagneticBrella_AttachedFly 38900 INC (IX+17) Increase the animation timer.
38903 LD A,(IX+4) Fetch the alien's Y position.
38906 CP 112 Compare it with 112.
38908 LD A,(IX+6) Fetch the vertical thrust.
38911 JR NC,Handler_MrMagneticBrella_ThrustUp Jump to Handler_MrMagneticBrella_ThrustUp if the alien is at or below mid-screen.
When above mid-screen, increase the downward thrust, up to a limit.
38913 AND A Jump to Handler_MrMagneticBrella_AttachedAddThrust if the thrust is negative.
38914 JP M,Handler_MrMagneticBrella_AttachedAddThrust
38917 CP 48 Jump to Handler_MrMagneticBrella_AttachedApplyThrust if the thrust is already at least 48.
38919 JR NC,Handler_MrMagneticBrella_AttachedApplyThrust
Handler_MrMagneticBrella_AttachedAddThrust 38921 ADD A,2 Add 2 to the thrust.
Apply the thrust to the alien's Y position, stopping at the ground line.
Handler_MrMagneticBrella_AttachedApplyThrust 38923 LD (IX+6),A Write the thrust back.
38926 SRA A Divide it by 16.
38928 SRA A
38930 SRA A
38932 SRA A
38934 ADD A,(IX+4) Add it to the alien's Y position.
38937 CP 176 Jump to Handler_MrMagneticBrella_AttachedWriteY if it is still above the ground line.
38939 JR C,Handler_MrMagneticBrella_AttachedWriteY
175 is the ground line.
38941 LD A,175 A=175.
Handler_MrMagneticBrella_AttachedWriteY 38943 LD (IX+4),A Write the Y position back.
Occasionally pick a new horizontal direction using RandomNumber.
38946 LD A,(24128) Jump to Handler_MrMagneticBrella_DetachIfTerrain if RandomNumber is zero.
38949 LD C,A
38950 AND A
38951 JR Z,Handler_MrMagneticBrella_DetachIfTerrain
38953 AND %01111111 Keep only bits 0-6.
38955 JR NZ,Handler_MrMagneticBrella_AccelerateFromFlag Jump to Handler_MrMagneticBrella_AccelerateFromFlag if the result is not zero.
38957 LD A,C Fetch the stored random byte.
38958 AND %10000000 Keep only bit 7.
38960 LD C,A Stash that sign bit.
38961 LD A,(IX+8) Fetch the actor flags.
38964 AND %01111111 Keep only bits 0-6.
38966 OR C Merge in the sign bit and write the flags back.
38967 LD (IX+8),A
Accelerate left or right from bit 7 of the flags.
Handler_MrMagneticBrella_AccelerateFromFlag 38970 BIT 7,(IX+8) Test bit 7 of the actor flags.
38974 LD A,(IX+5) Fetch the horizontal speed.
38977 JR NZ,Handler_MrMagneticBrella_CapSpeed Jump to Handler_MrMagneticBrella_CapSpeed if bit 7 is set.
When bit 7 is reset, speed up towards the right, up to a limit.
38979 AND A Jump to Handler_MrMagneticBrella_AddSpeed if the speed is negative.
38980 JP M,Handler_MrMagneticBrella_AddSpeed
38983 CP 48 Jump to Handler_MrMagneticBrella_WriteSpeedBack if the speed is already at least 48.
38985 JR NC,Handler_MrMagneticBrella_WriteSpeedBack
Handler_MrMagneticBrella_AddSpeed 38987 ADD A,2 Add 2 to the speed.
Handler_MrMagneticBrella_WriteSpeedBack 38989 LD (IX+5),A Write the speed back.
Stash the world X and rejoin the shared code at Handler_MrMagneticBrella_RestoreX.
Handler_MrMagneticBrella_StashWorldX 38992 LD H,(IX+3) Fetch the high byte of the world X.
38995 LD L,(IX+2) Fetch the low byte of the world X.
38998 PUSH HL Stash the world X on the stack.
38999 JP Handler_MrMagneticBrella_RestoreX Jump to Handler_MrMagneticBrella_RestoreX.
When below mid-screen, apply upward thrust.
Handler_MrMagneticBrella_ThrustUp 39002 AND A Jump to Handler_MrMagneticBrella_SubtractThrust if the thrust is positive.
39003 JP P,Handler_MrMagneticBrella_SubtractThrust
39006 CP 209 Jump to Handler_MrMagneticBrella_AttachedApplyThrust if the thrust is already below 209.
39008 JR C,Handler_MrMagneticBrella_AttachedApplyThrust
Handler_MrMagneticBrella_SubtractThrust 39010 SUB 2 Subtract 2 from the thrust.
39012 JR Handler_MrMagneticBrella_AttachedApplyThrust Jump to Handler_MrMagneticBrella_AttachedApplyThrust.
Handler_MrMagneticBrella_CapSpeed 39014 AND A Jump to Handler_MrMagneticBrella_SubtractSpeed if the speed is positive.
39015 JP P,Handler_MrMagneticBrella_SubtractSpeed
39018 CP 209 Jump to Handler_MrMagneticBrella_WriteSpeedBack if the speed is already below 209.
39020 JR C,Handler_MrMagneticBrella_WriteSpeedBack
Handler_MrMagneticBrella_SubtractSpeed 39022 SUB 2 Subtract 2 from the speed.
39024 JR Handler_MrMagneticBrella_WriteSpeedBack Jump to Handler_MrMagneticBrella_WriteSpeedBack.
When RandomNumber is zero, check for terrain under the alien. If there is some, detach the alien; otherwise carry on accelerating.
Handler_MrMagneticBrella_DetachIfTerrain 39026 CALL ReadTerrainCell Call ReadTerrainCell.
39029 LD A,D Jump to Handler_MrMagneticBrella_AccelerateFromFlag if the first terrain cell is empty.
39030 AND A
39031 JR Z,Handler_MrMagneticBrella_AccelerateFromFlag
39033 LD A,128 Write 128 to World_Slot_1_Flags.
39035 LD (24752),A
39038 LD (IX+8),0 Write 0 to the actor flags.
39042 JR Handler_MrMagneticBrella_StashWorldX Jump to Handler_MrMagneticBrella_StashWorldX.
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