Routines
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30084: Prepare Actor Sprite
Used by the routines at DisplayEntity and DrawEntity.
Does the same as PrepareOldSprite for the sprite of the actor in IX. As well as the screen address, it records the address of the first attribute cell in ActorSprite_Position, the width in character cells in ActorSprite_Width and the number of rows to draw in ActorSprite_RowsRemaining and ActorSprite_Rows. This is set up for the shifting routine at DrawActorSpriteRow.
Input
IX Actor
Output
C 0
DE Address of the first row of sprite data to draw
HL Screen address of the bottom row of the sprite
PrepareActorSprite 30084 CALL FetchActorSprite Fetch the address of the actor sprite using FetchActorSprite.
PrepareActorSprite_Position 30087 LD L,(IX+1) Fetch the horizontal co-ordinate of the actor.
30090 LD H,(IX+2) Fetch the vertical co-ordinate of the actor.
30093 LD A,L Fetch the horizontal co-ordinate.
30094 DEC A Decrease A by one.
30095 RLCA Multiply by 2.
30096 AND %00001110 Keep only bits 1-3.
30098 CP 14 Jump to PrepareActorSprite_Shift if this is not the maximum offset.
30100 JR NZ,PrepareActorSprite_Shift
30102 LD A,241 Use the offset which jumps to the code for sprites which are aligned to a character cell.
Self modifying code; this updates the operand of the JR command at 30392.
PrepareActorSprite_Shift 30104 LD (30393),A Write the offset to the JR command at 30393.
A sprite which is aligned to a character cell is two cells wide, otherwise it is three cells wide.
30107 LD A,2 Set the width to 2.
30109 JR Z,PrepareActorSprite_Width Jump to PrepareActorSprite_Width if the sprite is aligned to a character cell.
30111 INC A Set the width to 3.
PrepareActorSprite_Width 30112 LD (24344),A Write the width to the actor sprite width (ActorSprite_Width).
30115 CALL ClipSprite Clip the sprite using ClipSprite.
30118 LD (24351),HL Save the position of the actor sprite (ActorSprite_Position).
30121 CALL ScreenAddress Convert the position into a screen address using ScreenAddress.
30124 LD A,(DE) Fetch the height of the sprite.
30125 SUB C Subtract the number of rows which are not visible.
30126 JR NC,PrepareActorSprite_Rows Jump to PrepareActorSprite_Rows if there are any rows to draw.
30128 XOR A There are no rows to draw.
PrepareActorSprite_Rows 30129 LD (24346),A Set the number of rows of the actor sprite to draw (ActorSprite_RowsRemaining).
30132 LD (24343),A Set the number of rows of the actor sprite on the screen (ActorSprite_Rows).
30135 LD B,0 Set the high byte of the offset to 0.
30137 SLA C Multiply the number of hidden rows by 2.
30139 EX DE,HL Skip the hidden rows in the sprite data.
30140 ADD HL,BC
30141 EX DE,HL
30142 JR PrepareSprite_Finish Jump to PrepareSprite_Finish to finish.
View the equivalent code in;
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