Routines
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34859: Fire Shot
Used by the routine at FireRandomShot.
Starts a shot (type 28) from an object, in one of the three shot slots. The kind of shot is chosen by the caller using the value in ScratchValue.
Input
IX Address of the object that fires
Output
IY Address of the shot slot
FireShot 34859 PUSH IX Save the address of the object.
34861 LD A,3 Look for a free slot among three slots...
34863 LD IX,39380 ...starting at the first shot slot.
34867 CALL FindFreeSlot Search for a free slot.
34870 PUSH IX Copy the address of the slot into IY...
34872 POP IY
34874 POP IX ...and restore the address of the object.
34876 RET NZ Return if there are no free slots.
34877 LD A,(IX+17) Fetch the horizontal screen position of the object.
34880 CP 192 Return if it is off the right-hand side of the screen...
34882 RET NC
34883 CP 24 ...or off the left-hand side.
34885 RET C
34886 LD A,(23580) Fetch the kind of shot from ScratchValue.
34889 LD HL,35238 Use the table of shot flags at ShotTables, less one.
34892 CALL AddAToHL Add the kind of shot to the address.
34895 LD A,(HL) Fetch the flags for this kind of shot.
34896 LD (23581),A Store them in TileNumber.
34899 LD A,(IX+18) Fetch the vertical screen position of the object.
34902 BIT 7,(HL) Jump to FireShot_CheckHigh if bit 7 of the flags is clear.
34904 JR Z,FireShot_CheckHigh
34906 CP 88 Return if the object is too low down the screen for this shot.
34908 RET NC
FireShot_CheckHigh 34909 BIT 6,(HL) Jump to FireShot_Start if bit 6 of the flags is clear.
34911 JR Z,FireShot_Start
34913 CP 80 Return if the object is too high up the screen for this shot.
34915 RET C
FireShot_Start 34916 CALL SwapObjects Swap IX and IY, then copy the position of the object.
34919 CALL FreeObjectSlot Clear the slot of the shot.
34922 LD (IX+0),28 Make the object a shot.
34926 LD (IX+16),32 Set the flags of the shot.
34930 LD HL,35243 Use the table of shot speeds at ShotTables_Speeds.
34933 LD A,(23580) Fetch the kind of shot.
34936 ADD A,A Multiply it by four.
34937 ADD A,A
34938 CALL AddAToHL Add it to the address.
34941 LD A,(HL) Set the horizontal speed of the shot from the table.
34942 LD (IX+7),A
34945 INC HL
34946 LD A,(HL)
34947 LD (IX+9),A Set the vertical speed of the shot from the table.
34950 INC HL
34951 LD A,(HL)
34952 LD (IX+19),A Set the first state byte of the shot from the table.
34955 INC HL
34956 LD A,(HL)
34957 LD (IX+20),A Set the second state byte of the shot from the table.
34960 LD A,(23581) Fetch the flags for this kind of shot.
34963 AND %00001111 Keep the colour in the bottom four bits.
34965 LD B,A Copy it into the top four bits...
34966 ADD A,A
34967 ADD A,A
34968 ADD A,A
34969 ADD A,A
34970 OR B ...and set the attribute of the shot.
34971 LD (IX+13),A
34974 LD (IX+21),56 Set the lifetime of the shot to 56.
34978 CALL MoveObject Draw the shot.
34981 PUSH IY Swap IX and IY back again.
34983 PUSH IX
34985 POP IY
34987 POP IX
34989 LD A,(IY+19) Fetch the state of the object that fired the shot.
34992 AND %00001111 Keep the bottom four bits.
34994 JP Z,SetFallingSpeed Jump to SetFallingSpeed if it is zero.
34997 CP 5 Jump to SetRandomSpeed if it is 5.
34999 JP Z,SetRandomSpeed
35002 CP 6 Jump to SetRandomSpeed if it is 6.
35004 JP Z,SetRandomSpeed
35007 CP 7 Jump to ReverseVerticalSpeed if it is 7.
35009 JP Z,ReverseVerticalSpeed
35012 CP 10 Jump to FireShot_State0A if it is 10.
35014 JP Z,FireShot_State0A
35017 LD H,(IX+7) Fetch the horizontal speed of the shot...
35020 LD L,(IX+8)
35023 SRA H ...halve it...
35025 RR L
35027 LD (IY+7),H ...and give it to the object that fired.
35030 LD (IY+8),L
35033 LD A,(23581) Fetch the flags for this kind of shot.
35036 LD (IY+9),5 Set the vertical speed of the object to push it up.
35040 BIT 7,A Jump to FireShot_Sound if bit 7 of the flags is set.
35042 JR NZ,FireShot_Sound
35044 LD (IY+9),251 Otherwise set the vertical speed to push it down instead.
This entry point is used by the routines at SetRandomSpeed, SetFallingSpeed and ReverseVerticalSpeed.
FireShot_Sound 35048 LD A,(IY+0) Fetch the type of the object.
35051 INC A Increment it.
35052 CALL NZ,PlayNoiseBurst Play a sound if the object is active.
35055 RET Return.
FireShot_State0A 35056 LD (IY+7),6 Set the horizontal speed of the object to six...
35060 LD (IY+8),0 ...and clear its other speeds.
35064 LD (IY+9),0
35068 LD (IY+10),0
35072 LD A,(23580) Fetch the kind of shot.
35075 CP 7 Jump to FireShot_Sound if it is 7.
35077 JR Z,FireShot_Sound
35079 LD (IY+7),250 Otherwise reverse the horizontal speed.
35083 JR FireShot_Sound Jump to FireShot_Sound.
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