Routines
Prev: 37798 Up: Map Next: 37980
37864: Handler: Falling Platform
Drop a thrown platform (type 47): speed it up under gravity and move it along. When it reaches the ground line, stamp it into the terrain and free the slot.
Input
IX Actor slot
Increase the downward thrust by two, up to a cap of 48.
Handler_FallingPlatform 37864 LD A,(IX+6) Fetch the vertical thrust.
37867 CP 48 Jump to Handler_FallingPlatform_ApplyGravity if it is already at least 48.
37869 JR NC,Handler_FallingPlatform_ApplyGravity
37871 INC (IX+6) Increase the thrust by two.
37874 INC (IX+6)
Turn the thrust into a Y movement and test for the ground.
Handler_FallingPlatform_ApplyGravity 37877 SRA A Divide the thrust by 16.
37879 SRA A
37881 SRA A
37883 SRA A
37885 ADD A,(IX+4) Add it to the actor's Y position.
37888 LD (IX+4),A Write the Y position back.
37891 CP 176 Jump to Handler_FallingPlatform_AddSpeed if the actor is still above the ground line.
37893 JR C,Handler_FallingPlatform_AddSpeed
When the actor has hit the ground, stamp tile 3 into two terrain cells.
37895 CALL ReadTerrainCell Call ReadTerrainCell.
Snap the actor to the ground line.
37898 LD A,183 Write 183 to the actor's Y position.
37900 LD (IX+4),A
37903 LD DE,28672 DE=TerrainData_Active.
37906 EX DE,HL Point HL at the terrain cell.
37907 ADD HL,DE
37908 LD (HL),3 Write tile 3 into that cell.
Step to the next cell, wrapping the index, and stamp it too.
37910 INC DE Move onto the next cell.
37911 LD A,D Fetch the high byte.
37912 AND %00000011 Keep only bits 0-1.
37914 LD D,A Write it back to D.
37915 LD HL,28672 Point HL at that terrain cell.
37918 ADD HL,DE
37919 LD (HL),3 Write tile 3 into that cell.
Align the actor to a character column, clear the terrain pixels beneath it and free the slot.
37921 LD A,(IX+2) Fetch the low byte of the world X.
37924 AND %11111000 Keep only bits 3-7.
37926 LD L,A Align the world X to a character column.
37927 LD (IX+2),L
37930 CALL ClearTerrainUnderActor Call ClearTerrainUnderActor.
37933 CALL DrawSprite Call DrawSprite.
37936 LD (IX+0),0 Write 0 to the actor type.
37940 RET Return.
Add the horizontal speed and redraw the actor.
Handler_FallingPlatform_AddSpeed 37941 LD A,(IX+5) Fetch the horizontal speed.
37944 SRA A Divide it by 16.
37946 SRA A
37948 SRA A
37950 SRA A
37952 LD C,A Copy the step into C and clear B.
37953 LD B,0
37955 JP P,Handler_FallingPlatform_WriteWorldX Jump to Handler_FallingPlatform_WriteWorldX if the step is positive.
37958 LD B,255 Set B=255 for a negative step.
Add the step to the world X and redraw the actor.
Handler_FallingPlatform_WriteWorldX 37960 LD L,(IX+2) Fetch the low byte of the world X.
37963 LD H,(IX+3) Fetch the high byte of the world X.
37966 ADD HL,BC Add the step to the world X.
37967 LD (IX+3),H Write the high byte back.
37970 LD (IX+2),L Write the low byte back.
37973 CALL DrawSprite Call DrawSprite.
37976 CALL ColouriseSprite Call ColouriseSprite.
37979 RET Return.
Prev: 37798 Up: Map Next: 37980