Routines
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8826: Fetch And Draw
Look up the actor sprite, clip it against the left and right screen edges, and cache its graphic pointer and screen address on the actor.
Input
IX Actor slot
Look up the actor sprite and test whether it is on-screen.
FetchAndDraw 8826 CALL FetchActorSprite Call FetchActorSprite.
8829 LD L,(IX+$02) Fetch the actor's world X position.
882C LD H,(IX+$03)
882F LD BC,($607A) Subtract the scroll position at Jetman_Position.
8833 AND A
8834 SBC HL,BC
8836 LD BC,$0068 Add the 0068 draw offset.
8839 ADD HL,BC
883A LD A,H Fetch the high byte of the screen column.
883B AND %00011111 Keep only bits 0-4.
883D JR Z,ReadSpriteHeader Jump to ReadSpriteHeader if the actor is on-screen.
883F ADD A,$E1 Jump to ClearSpriteCache if the column is not 1F.
8841 JR NZ,ClearSpriteCache
Clip a sprite that straddles the left edge.
8843 LD A,L Arithmetic-shift the column down by three.
8844 SRA A
8846 SRA A
8848 SRA A
884A JP P,ClearSpriteCache Jump to ClearSpriteCache if the result is positive.
884D LD B,A Store the shifted column.
884E AND %00001111 Keep only bits 0-3.
8850 LD ($87EE),A Write the skip to 87EE and *IX+09.
8853 LD (IX+$09),A
Work out how much of the sprite width is visible and cache the visible width and height.
8856 LD A,(DE) Fetch the sprite width and add the shifted column.
8857 INC DE
8858 LD C,A
8859 ADD A,B
885A JP M,ClearSpriteCache Jump to ClearSpriteCache if that sum is zero or negative.
885D JR Z,ClearSpriteCache
885F LD B,A Copy the visible width into B.
8860 LD ($5E57),A Write the visible width to SpriteWidth and *IX+0B.
8863 LD (IX+$0B),A
8866 LD A,(DE) Copy the next header byte into SpriteRowsLeft, SpriteHeight and *IX+0A.
8867 INC DE
8868 LD ($5E59),A
886B LD ($5E58),A
886E LD (IX+$0A),A
Skip the graphic bytes hidden off the left edge.
8871 LD A,C A=width-visible width (the bytes hidden on the left).
8872 SUB B
FetchAndDraw_Loop 8873 INC DE Skip graphic bytes until the visible strip starts.
8874 DEC A
8875 JR NZ,FetchAndDraw_Loop
8877 LD L,$00 Set the screen column to 00.
Cache the visible strip and draw it.
FetchAndDraw_StoreColumn 8879 LD (IX+$01),L Store the screen column.
887C LD H,(IX+$04) Fetch the actor Y.
887F CALL ScreenAddress Call ScreenAddress.
8882 LD (IX+$0C),E Cache the graphic pointer and screen address on the actor.
8885 LD (IX+$0D),D
8888 LD (IX+$0E),L
888B LD (IX+$0F),H
888E LD C,$00 Clear the row counter.
8890 RET Return.
Prev: 8807 Up: Map Next: 8891