Routines
Prev: 27815 Up: Map Next: 27960
27831: Handle Sugar
The handler for the sugar (IDs 8 and 9), which drifts about the screen. Byte 4 of the actor is the horizontal speed, and byte 5 is the vertical speed. Every 32 frames new random speeds are chosen (see SetRandomSpeeds); they are both either 2 or 254 (-2). The sugar bounces off the sides and the top and bottom of the play area, and as it goes it also moves up and down in a wave, which is made from the frame counter in byte 7 of the actor.
While the sugar is still entering from the right of the screen (a horizontal co-ordinate of 196 or more) it can't hit Charlie or be hit.
Input
IX Actor
HandleSugar 27831 CALL StoreEntity Record the position of the sprite using StoreEntity.
27834 LD HL,24347 Point HL at ActorsInPlay.
27837 INC (HL) Increase the number of actors in play by one.
27838 LD A,(IX+1) Fetch the horizontal co-ordinate.
27841 CP 196 Jump to HandleSugar_Move if the sugar is still entering from the right.
27843 JR NC,HandleSugar_Move
27845 CALL TestCharlieCollision Test whether the sugar has hit Charlie using TestCharlieCollision.
27848 DEC E Has Charlie been hit (is E now zero)?
27849 JP Z,LoseHat Jump to LoseHat if Charlie has been hit.
27852 CALL TestFlourCollision Test whether a flour shot has hit the sugar using TestFlourCollision.
27855 BIT 7,(IX+0) Jump to HandleHitActor if the sugar has been hit.
27859 JP NZ,HandleHitActor
HandleSugar_Move 27862 INC (IX+7) Increase the frame counter in byte 7 of the actor by one.
27865 LD (IX+3),68 Set the actor colour to 68 (green).
27869 LD A,(IX+7) Fetch the frame counter.
27872 AND %00011111 Keep only bits 0-4.
27874 JR Z,HandleSugar_NewSpeeds Jump to HandleSugar_NewSpeeds if the counter is a multiple of 32 to change speed.
27876 LD A,(IX+1) Fetch the horizontal co-ordinate.
27879 ADD A,(IX+4) Add the horizontal speed.
27882 LD (IX+1),A Update the horizontal co-ordinate.
27885 CP 192 Jump to HandleSugar_RightEdge if the sugar has reached the right edge.
27887 JR NC,HandleSugar_RightEdge
27889 CP 4 Jump to HandleSugar_LeftEdge if the sugar has reached the left edge.
27891 JR C,HandleSugar_LeftEdge
Make the offset for the wave from the frame counter. For each of the eight values of bits 0-2 of the counter it is 3 252 253 254 0 1 2 and 3.
HandleSugar_Wave 27893 LD A,(IX+7) Fetch the frame counter.
27896 AND %00000011 Keep only bits 0-1.
27898 BIT 2,(IX+7) Jump to HandleSugar_Vertical if bit 2 of the frame counter is set.
27902 JR NZ,HandleSugar_Vertical
27904 NEG Negate A.
27906 XOR %00000011 Flip bits 0-1.
HandleSugar_Vertical 27908 ADD A,(IX+5) Add the vertical speed.
27911 ADD A,(IX+2) Add the vertical co-ordinate.
27914 CP 32 Jump to HandleSugar_Top if the sugar has reached the top.
27916 JR C,HandleSugar_Top
27918 CP 160 Jump to HandleSugar_Bottom if the sugar has reached the bottom.
27920 JR NC,HandleSugar_Bottom
27922 LD (IX+2),A Update the vertical co-ordinate.
HandleSugar_Draw 27925 CALL DisplayEntity Erase the sprite and draw it in its new position using DisplayEntity.
27928 JP ColourSprite Jump to ColourSprite to colour the sprite.
The sugar has reached the right edge, so move it left.
HandleSugar_RightEdge 27931 LD (IX+4),254 Set the horizontal speed to 254 (-2, moving left).
27935 JR HandleSugar_Wave Jump to HandleSugar_Wave.
The sugar has reached the left edge, so move it right.
HandleSugar_LeftEdge 27937 LD (IX+4),2 Write 2 to the horizontal speed.
27941 JR HandleSugar_Wave Jump to HandleSugar_Wave.
The sugar has reached the top, so move it down.
HandleSugar_Top 27943 LD (IX+5),2 Write 2 to the vertical speed.
27947 JR HandleSugar_Draw Jump to HandleSugar_Draw.
The sugar has reached the bottom, so move it up.
HandleSugar_Bottom 27949 LD (IX+5),254 Write 254 to the vertical speed.
27953 JR HandleSugar_Draw Jump to HandleSugar_Draw.
Choose new speeds. A is the new vertical speed, so it is added to the vertical co-ordinate twice.
HandleSugar_NewSpeeds 27955 CALL SetRandomSpeeds Set random horizontal and vertical speeds using SetRandomSpeeds.
27958 JR HandleSugar_Vertical Jump to HandleSugar_Vertical.
Prev: 27815 Up: Map Next: 27960