Routines
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53762: Follow Path
Used by the routine at MoveEntity.
Moves an entity that is following a path from the level data, which is the case when fields 36 and 37 are not both zero. Bits 0-2 of field 37 choose a three-byte step from a table. Bits 6-7 of field 36 can replace that step: 64 lowers the entity and can play the long buzz, 128 moves it back along y, and 192 moves it on along x. The three bytes of a looked-up step are added to x, y and z. A step above 8 finishes the path. The player can be scored and shown the filled cup, and a path position is then copied into the entity before the falling sweep plays.
Input
IX The entity
FollowPath 53762 RES 7,(IX+17) Clear the moving flag.
53766 RES 7,(IX+30) Clear the fast flag.
53770 CALL FindPathEntry Find the path entry.
53773 PUSH HL Remember the entry.
53774 LD A,(IX+37) Read the low byte of the path.
53777 AND %00000111 Keep the step number in bits 0-2.
53779 JR NZ,FollowPath_Lookup Look the step up when a number is set.
53781 DEC HL Use the two bytes just before the entry.
53782 DEC HL
53783 JR FollowPath_Step Join the stored step.
FollowPath_Lookup 53785 DEC A Turn the step number into a table offset.
53786 ADD A,A
53787 ADD A,A
53788 CALL AddToAddress Look the offset up.
53791 LD C,(HL) Read the x step, the y step and the z step.
53792 INC HL
53793 LD B,(HL)
53794 INC HL
53795 LD E,(HL)
FollowPath_Step 53796 LD (54134),HL Remember where the path continues.
53799 LD A,(IX+36) Read the high byte of the path.
53802 AND %11000000 Keep the nudge in bits 6-7.
53804 JR Z,FollowPath_Z Use the looked-up step when there is no nudge.
53806 CP 64 Lower the entity when the nudge is 64.
53808 JR NZ,FollowPath_Nudge
53810 LD A,(IX+37) Read the low byte of the path again.
53813 CP 64 Play the long buzz when that byte is 64 as well.
53815 CALL Z,PlayLongBuzz
53818 LD BC,0 Clear the x step and the y step.
53821 LD E,254 Lower the entity by two.
53823 JR FollowPath_Z Add the step.
FollowPath_Nudge 53825 LD B,254 Move the entity back along y, and clear the other steps.
53827 LD C,0
53829 LD E,C
53830 CP 128 Keep that nudge when the bits are 128.
53832 JR Z,FollowPath_Z
53834 LD C,2 Move the entity on along x instead.
53836 LD B,E
FollowPath_Z 53837 LD H,(IX+8) Fetch the z coordinate.
53840 LD L,(IX+9)
53843 LD D,0 Sign-extend the z step.
53845 BIT 7,E
53847 JR Z,FollowPath_AddZ
53849 DEC D
FollowPath_AddZ 53850 ADD HL,DE Add the z step to the z coordinate.
53851 LD (IX+8),H
53854 LD (IX+9),L
53857 LD E,C Sign-extend the x step.
53858 BIT 7,E
53860 LD D,0
53862 JR Z,FollowPath_X
53864 DEC D
FollowPath_X 53865 LD H,(IX+2) Fetch the x coordinate.
53868 LD L,(IX+3)
53871 ADD HL,DE Add the x step to the x coordinate.
53872 LD (IX+2),H
53875 LD (IX+3),L
53878 LD E,B Sign-extend the y step.
53879 BIT 7,E
53881 LD D,0
53883 JR Z,FollowPath_Y
53885 DEC D
FollowPath_Y 53886 LD H,(IX+5) Fetch the y coordinate.
53889 LD L,(IX+6)
53892 ADD HL,DE Add the y step to the y coordinate.
53893 LD (IX+5),H
53896 LD (IX+6),L
A step above 8 finishes the path. A step of exactly 8 or a step number that no longer matches the entry, reads the next path byte.
53899 POP HL Restore the path entry.
53900 LD A,(IX+37) A step of 8 reads the next path byte.
53903 SUB 8
53905 JP Z,FollowPath_Next
53908 JR NC,FollowPath_Finish A larger step finishes the path.
53910 LD A,(IX+37) Read field 37 again.
53913 AND %00000111 Use the step number.
53915 DEC HL Compare it with the byte before the entry.
53916 CP (HL)
53917 JP NZ,FollowPath_Next Read the next path byte when they differ.
53920 LD A,(IX+36) Read field 36.
53923 AND %11000000 Use bits 6-7 of the path.
53925 JR Z,FollowPath_Reward Copy the path position when those bits are clear.
53927 LD A,(IX+0) Only the player finishes the path here.
53930 DEC A
53931 JR NZ,FollowPath_Clear
53933 LD HL,0 Set the player's vertical speed to 8704.
53936 LD (46418),HL
53939 LD (23808),A Clear the jump counter.
53942 LD A,(IX+16) Read the width byte.
53945 AND %11110000 Use the countdown nibble.
53947 LD (IX+16),A Clear the sprite width.
53950 LD (IX+26),0 Clear the fraction of the speed.
FollowPath_Clear 53954 XOR A Clear field 36.
53955 LD (IX+36),A
FollowPath_Finish 53958 LD (IX+37),A Clear field 37 and return.
53961 RET
The byte stored by FindPathEntry chooses the player's reward. Zero scores 1280. Any other byte, the first time, scores 96 and draws the cup.
FollowPath_Reward 53962 LD A,(IX+0) Only the player is rewarded.
53965 DEC A
53966 JR NZ,FollowPath_1
53968 EXX Switch to the reward byte.
53969 LD A,0 Score 1280 when the path byte is zero.
53971 AND A
53972 JR NZ,FollowPath_Cup
53974 LD BC,1280 Add a score of 1280.
53977 CALL AddScore
53980 JR FollowPath_0 Skip the cup.
FollowPath_Cup 53982 LD A,(57084) The cup is shown only once.
53985 AND A
53986 JR NZ,FollowPath_0
53988 LD A,(46428) Read the player's animation counter.
53991 AND %11110000 Use the high nibble of the animation.
53993 OR %00000101 Set the low nibble to 5.
53995 LD (46428),A Keep that animation.
53998 LD A,5 Set the control byte to 5.
54000 LD (43901),A
54003 LD BC,96 Add a score of 96.
54006 CALL AddScore
54009 LD HL,26632 Draw the filled cup.
54012 LD DE,25752
54015 CALL DrawPicture
54018 LD A,1 Remember that the cup has been shown.
54020 LD (57084),A
FollowPath_0 54023 EXX Switch back.
FollowPath_1 54024 DEC HL Step back to the path's position.
54025 LD A,(IX+36) Read field 36.
54028 AND %00111111 Use bits 0-5 of the path.
54030 OR (HL) Combine them with the path byte and keep them.
54031 LD B,A
54032 LD (IX+36),A
54035 LD A,(IX+37) Read field 37.
54038 AND %00000111 Use the step number.
54040 OR %00100000 Mark the step with bit 5.
54042 LD (IX+37),A Keep the marked step.
54045 DEC HL Copy the path's coordinates into the entity.
54046 LD A,(HL)
54047 LD (IX+9),A
54050 DEC HL
54051 LD A,(HL)
54052 LD (IX+8),A
54055 DEC HL
54056 LD A,(HL)
54057 LD (IX+6),A
54060 DEC HL
54061 LD A,(HL)
54062 LD (IX+5),A
54065 DEC HL
54066 LD A,(HL)
54067 LD (IX+3),A
54070 DEC HL
54071 LD A,(HL)
54072 LD (IX+2),A
54075 LD A,B Bring the new path flags back.
54076 AND %11000000 Use bits 6-7 of those flags.
54078 CP 144 Place the entity on y unless the flags are 192.
54080 JR NC,FollowPath_PlaceX
54082 LD A,(IX+6) Read the low byte of y.
54085 AND %11110000 Use the high nibble of y.
54087 OR %00001000 Force the low nibble to 8.
54089 LD (IX+6),A Keep that y position.
54092 LD A,16 Shift x by half of 16 less the x extent.
54094 SUB (IX+11)
54097 SRL A
54099 ADD A,(IX+3)
54102 LD (IX+3),A
54105 JR FollowPath_2 Join the falling sweep.
FollowPath_PlaceX 54107 LD A,(IX+3) Read the low byte of x.
54110 AND %11110000 Use the high nibble of x.
54112 OR %00001000 Force the low nibble to 8.
54114 LD (IX+3),A Keep that x position.
54117 LD A,16 Shift y by half of 16 less the y extent.
54119 SUB (IX+12)
54122 SRL A
54124 ADD A,(IX+6)
54127 LD (IX+6),A
FollowPath_2 54130 JP PlayFallingSweep Play the falling sweep.
FollowPath_Next 54133 LD HL,0 Read the next byte of the path table.
54136 LD DE,5
54139 ADD HL,DE
54140 LD A,(HL) Use it as field 37.
54141 LD (IX+37),A
54144 LD A,(IX+36) Read field 36.
54147 AND %00111111 Use bits 0-5 of the path.
54149 LD (IX+36),A Clear bits 6-7 of the path.
54152 RET Return.
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