Routines
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41467: Clip Sprite Vertically
Used by the routines at ClipSecondSprite and ClipFirstSprite.
Clips a sprite so that it lies between 23 and 183 on the vertical axis, which is the playfield. The position of a sprite is its bottom row and its rows go up from there, so rows below the playfield are skipped by moving on the address of the data, and rows above it are not drawn.
Input
A Vertical position
B Number of rows
DE Address of the first row of data
H Width in bytes
Output
B Number of rows to draw
DE Address of the first row of data to draw
L Vertical position of the first row to draw
ClipSpriteVertically 41467 LD L,A Store the vertical position.
41468 SUB 23 Subtract 23, the top of the playfield.
41470 SUB B Subtract the number of rows.
41471 JR NC,ClipSpriteVertically_Top Jump to ClipSpriteVertically_Top if the sprite does not go past the top.
41473 LD A,L Fetch the vertical position.
41474 SUB 23 Subtract 23 to get the number of rows that fit.
41476 LD B,A Store it as the number of rows.
41477 RET Return.
ClipSpriteVertically_Top 41478 LD A,L Fetch the vertical position.
41479 SUB 183 Subtract 183, the bottom of the playfield.
41481 RET Z Return if the sprite starts exactly at the bottom.
41482 RET C Return if the sprite starts above the bottom.
41483 LD L,A Store the number of rows that are below the bottom.
41484 LD A,B Fetch the number of rows.
41485 SUB L Take off the rows that are below the bottom.
41486 LD B,A Store it.
41487 XOR A Clear A.
ClipSpriteVertically_Skip 41488 ADD A,H Add the width for each row that is below the bottom.
41489 DEC L Count down.
41490 JR NZ,ClipSpriteVertically_Skip Loop back to ClipSpriteVertically_Skip for each row.
41492 EX DE,HL Put the address of the data in HL.
41493 CALL AddAToHL Skip the data for the rows below the bottom.
41496 EX DE,HL Put the address back in DE.
41497 LD L,183 Start at the bottom of the playfield.
41499 RET Return.
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