Routines
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29861: Set Up Previous Sprite
Used by the routine at DrawSprite.
Sprites are drawn by erasing the previous image and drawing the new one at the same time, a row at a time. The routines from here to DisplayEntity_Compare prepare the two images: the main registers hold one sprite and the shadow registers hold the other. Each is set up with the screen address in HL, the sprite width in B, a row count of zero in C and the sprite data pointer in DE.
This entry point finds the previous sprite from the temporary actor state at Actor, using PrepareOldSprite to get its graphic.
SetUpPreviousSprite 29861 CALL PrepareOldSprite Call PrepareOldSprite.
This entry point is used by the routines at UpdateBloomingFlower, UpdateStreamer, UpdateLeaf and DrawSprite.
Sets up the previous sprite using the sprite data address in DE, rather than looking it up.
SetUpPreviousSprite_Address 29864 LD HL,(24075) Fetch the previous X and Y position from Actor.
This entry point is used by the routine at AnimateExplosion.
The first byte of the sprite is a horizontal offset in pixels.
SetUpPreviousSprite_Offset 29867 LD A,(DE) Fetch the horizontal offset.
29868 INC DE Move onto the sprite width.
29869 ADD A,L Add the horizontal offset to the X position.
29870 LD L,A Store the result back in L.
29871 CALL ScreenAddress Convert the position into a screen address using ScreenAddress.
29874 LD A,(DE) Fetch the sprite width.
29875 LD B,A Set the width counter in B to the sprite width.
29876 INC DE Move onto the sprite height.
29877 LD A,(DE) Fetch the sprite height.
29878 LD (24080),A Store it in 24080 as the height of the previous sprite.
SetUpSprite_Finish 29881 LD C,0 Set the row count in C to 0 (no rows have been drawn yet).
29883 INC DE Move onto the first byte of the sprite graphic data.
29884 RET Return.
This entry point is used by the routine at DrawSprite.
Sets up the sprite of the actor in IX, using ActorMoveSprite to get its graphic.
SetUpSprite 29885 CALL ActorMoveSprite Call ActorMoveSprite.
This entry point is used by the routines at UpdateBloomingFlower, UpdateStreamer, UpdateLeaf and DrawSprite.
Sets up the sprite using the sprite data address in DE, at the position held in the actor object.
SetUpSprite_Address 29888 LD L,(IX+1) Fetch the X and Y position from *IX+1 and *IX+2.
29891 LD H,(IX+2)
This entry point is used by the routine at DrawCubbyHoleItem.
SetUpSprite_Offset 29894 LD A,(DE) Fetch the horizontal offset.
29895 INC DE Move onto the sprite width.
29896 ADD A,L Add the horizontal offset to the X position.
29897 LD L,A Store the result back in L.
29898 LD (24090),HL Store the screen position in SpritePosition.
29901 CALL ScreenAddress Convert the position into a screen address using ScreenAddress.
29904 LD A,(DE) Fetch the sprite width.
29905 LD B,A Set the width counter in B to the sprite width.
29906 LD (24079),A Store it in NewSprite_Width.
29909 INC DE Move onto the sprite height.
29910 LD A,(DE) Fetch the sprite height.
29911 LD (24081),A Store it in 24081 as the height of the new sprite.
29914 LD (24078),A Store it in 24078.
29917 JR SetUpSprite_Finish Jump to SetUpSprite_Finish.
This entry point is used by the routine at UpdateFlower.
Moves a sprite using the same sprite data in DE for both the previous image (erased) and the new image (drawn).
ReplaceSprite 29919 PUSH DE Stash the sprite data pointer on the stack.
29920 CALL SetUpPreviousSprite_Address Set up the previous sprite using SetUpPreviousSprite_Address.
29923 EXX Switch to the shadow registers.
29924 POP DE Restore the sprite data pointer from the stack.
29925 CALL SetUpSprite_Address Set up the new sprite using SetUpSprite_Address.
29928 EXX Switch to the shadow registers.
29929 JR DisplayEntity_Compare Jump to DisplayEntity_Compare.
This entry point is used by the routines at UpdateSprayCan, DrawObject and UpdateBonusItem.
Display Entity. Erases the previous sprite of the actor in IX and draws the new one.
Before After DisplayEntity After ColouriseSprite
move-sprite-before move-sprite-drawn move-sprite-coloured
DisplayEntity 29931 CALL SetUpSprite Set up the new sprite using SetUpSprite.
29934 EXX Switch to the shadow registers.
29935 CALL SetUpPreviousSprite Set up the previous sprite using SetUpPreviousSprite.
This entry point is used by the routines at UpdateBloomingFlower, UpdateStreamer and UpdateLeaf.
Work out how many rows of one sprite lie beyond the other.
DisplayEntity_Compare 29938 LD A,(24076) Fetch the previous Y position from 24076.
29941 SUB (IX+2) Subtract the new Y position.
29944 JP Z,MaskSprite_Finish_Previous Jump to MaskSprite_Finish_Previous if the two sprites start on the same row.
29947 JP M,DisplayEntity_NewLower Jump to DisplayEntity_NewLower if the new sprite starts lower down the screen.
29950 LD C,A Store the number of extra rows in C.
29951 LD A,(24080) Fetch the height of the previous sprite from 24080.
29954 CP C Compare it with the number of extra rows.
29955 JP C,MaskSprite_Finish_Previous Jump to MaskSprite_Finish_Previous if the sprites do not overlap.
29958 SUB C Subtract the extra rows from the height of the previous sprite.
29959 LD (24080),A Write it back to 24080.
29962 JP MaskSprite Jump to MaskSprite to erase the extra rows of the previous sprite first.
The new sprite starts lower down the screen, so its extra rows are drawn first.
DisplayEntity_NewLower 29965 EXX Switch to the shadow registers.
29966 NEG Make the number of extra rows positive.
29968 LD C,A Store the number of extra rows in C.
29969 LD A,(24081) Fetch the height of the new sprite from 24081.
29972 CP C Compare it with the number of extra rows.
29973 JP C,MaskSprite_Finish Jump to MaskSprite_Finish if the sprites do not overlap.
29976 SUB C Subtract the extra rows from the height of the new sprite.
29977 JP MaskSprite_Finish_ClearNew Jump to MaskSprite_Finish_ClearNew.
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