Routines
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50280: Draw Strip
Used by the routines at DrawCell and DrawStripsLeftToRight.
Draws one tile of the edge of a cell of the town, if its position is inside the area where the town is drawn, which is from 17 to 207 horizontally and below 256 vertically. The tile number comes from the list at IY, and is changed to the number of an image by a table at TileImageNumbers and then by the swap flag.
Input
IY The address of the tile in its list
C One to swap the image for the other of its pair
Return if the tile is outside the play area horizontally.
DrawStrip 50280 LD DE,(41550) Fetch ScreenHorizontalPosition into DE.
50284 LD HL,207 Return if it is further to the right than 207.
50287 AND A
50288 SBC HL,DE
50290 RET C
50291 LD HL,16 Return if it is not further to the right than 16.
50294 SBC HL,DE
50296 RET NC
Return if the tile is off the screen vertically.
50297 LD HL,(41552) Fetch ScreenVerticalPosition.
50300 LD A,H Return if the high byte is not zero.
50301 AND A
50302 RET NZ
50303 LD D,L Keep the low byte of the vertical position in D.
Fetch the tile and find its image.
50304 LD A,C Fetch the swap flag.
50305 PUSH BC Stash the count of tiles on the stack.
50306 LD C,(IY+0) Fetch the tile number into BC.
50309 LD B,0
50311 LD HL,24108 Find the entry for the tile in TileImageNumbers.
50314 ADD HL,BC
50315 XOR (HL) Combine it with the swap flag, to make the number of the image.
50316 LD BC,35374 Point BC at EdgeImagePointers.
Find the address of the image.
50319 CALL GetTableEntry Call GetTableEntry.
Draw the image.
50322 CALL DrawStripGraphic Call DrawStripGraphic.
50325 POP BC Restore the count of tiles from the stack.
50326 RET Return.
View the equivalent code in;
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