Routines
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93E8: Handler: Falling Platform
Drop a thrown platform (type 2F): 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 30.
Handler_FallingPlatform 93E8 LD A,(IX+$06) Fetch the vertical thrust.
93EB CP $30 Jump to Handler_FallingPlatform_ApplyGravity if it is already at least 30.
93ED JR NC,Handler_FallingPlatform_ApplyGravity
93EF INC (IX+$06) Increase the thrust by two.
93F2 INC (IX+$06)
Turn the thrust into a Y movement and test for the ground.
Handler_FallingPlatform_ApplyGravity 93F5 SRA A Divide the thrust by 10.
93F7 SRA A
93F9 SRA A
93FB SRA A
93FD ADD A,(IX+$04) Add it to the actor's Y position.
9400 LD (IX+$04),A Write the Y position back.
9403 CP $B0 Jump to Handler_FallingPlatform_AddSpeed if the actor is still above the ground line.
9405 JR C,Handler_FallingPlatform_AddSpeed
When the actor has hit the ground, stamp tile 03 into two terrain cells.
9407 CALL ReadTerrainCell Call ReadTerrainCell.
Snap the actor to the ground line.
940A LD A,$B7 Write B7 to the actor's Y position.
940C LD (IX+$04),A
940F LD DE,$7000 DE=TerrainData_Active.
9412 EX DE,HL Point HL at the terrain cell.
9413 ADD HL,DE
9414 LD (HL),$03 Write tile 03 into that cell.
Step to the next cell, wrapping the index, and stamp it too.
9416 INC DE Move onto the next cell.
9417 LD A,D Fetch the high byte.
9418 AND %00000011 Keep only bits 0-1.
941A LD D,A Write it back to D.
941B LD HL,$7000 Point HL at that terrain cell.
941E ADD HL,DE
941F LD (HL),$03 Write tile 03 into that cell.
Align the actor to a character column, clear the terrain pixels beneath it and free the slot.
9421 LD A,(IX+$02) Fetch the low byte of the world X.
9424 AND %11111000 Keep only bits 3-7.
9426 LD L,A Align the world X to a character column.
9427 LD (IX+$02),L
942A CALL ClearTerrainUnderActor Call ClearTerrainUnderActor.
942D CALL DrawSprite Call DrawSprite.
9430 LD (IX+$00),$00 Write 00 to the actor type.
9434 RET Return.
Add the horizontal speed and redraw the actor.
Handler_FallingPlatform_AddSpeed 9435 LD A,(IX+$05) Fetch the horizontal speed.
9438 SRA A Divide it by 10.
943A SRA A
943C SRA A
943E SRA A
9440 LD C,A Copy the step into C and clear B.
9441 LD B,$00
9443 JP P,Handler_FallingPlatform_WriteWorldX Jump to Handler_FallingPlatform_WriteWorldX if the step is positive.
9446 LD B,$FF Set B=FF for a negative step.
Add the step to the world X and redraw the actor.
Handler_FallingPlatform_WriteWorldX 9448 LD L,(IX+$02) Fetch the low byte of the world X.
944B LD H,(IX+$03) Fetch the high byte of the world X.
944E ADD HL,BC Add the step to the world X.
944F LD (IX+$03),H Write the high byte back.
9452 LD (IX+$02),L Write the low byte back.
9455 CALL DrawSprite Call DrawSprite.
9458 CALL ColouriseSprite Call ColouriseSprite.
945B RET Return.
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