Routines
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40832: Prepare Draw 2/ 3 Byte Sprite
Used by the routines at RemoveEntity and DisplayEntity.
Gets everything ready to draw (or erase) the sprite at the position which was last recorded by StoreEntity. Sprites are drawn using the exclusive OR operation, so drawing a sprite for a second time erases it.
The number of rows to draw is written to Old_Sprite_Row_Count, and the shifting routine at DrawOldSpriteRow_Aligned is set up to move the sprite along by the position MOD 8 pixels.
Output
C 0
DE The address of the first row of sprite data to draw
HL The screen address of the bottom row of the sprite
PrepDraw23 40832 CALL GetSpriteA Fetch the address of the old sprite with GetSpriteA.
PrepDraw23_NoFetch 40835 LD HL,(24086) HL=Previous_X_Position (the saved X position in L and the saved Y position in H).
40838 LD A,L Fetch the X position.
40839 DEC A Decrease A by one.
40840 RLCA Multiply by 2.
40841 AND %00001110 Keep only bits 1-3.
40843 CP 14 Jump to PrepDraw23_Shift if this is not the maximum offset.
40845 JR NZ,PrepDraw23_Shift
40847 LD A,232 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 40677.
PrepDraw23_Shift 40849 LD (40677),A Write the offset to 40677.
40852 CALL ScreenAddress Call ScreenAddress to get the screen address of the position.
40855 LD A,(DE) Fetch the number of rows in the sprite (the first byte of the sprite data).
40856 LD (24088),A Write the number of rows to Old_Sprite_Row_Count.
This entry point is used by the routine at PrepDraw2.
PrepDraw23_Finish 40859 LD C,0 C=0.
40861 INC DE Move past the height byte.
40862 RET Return.
View the equivalent code in;
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