Routines
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57443: Check Walls Vertical First
Used by the routines at TestCellMovingRight and TestCellMovingLeft.
Tests an object against the walls in a cell, by testing it against each rectangle of the tile of the cell in turn, with the position along the Y axis first. The rectangles are four bytes each (the X and Y positions of the centre, then the half width and half depth), and a zero X position ends the list.
Input
DE X position to test
HL Y position to test
IX Object
Output
A The depth into the wall along the X axis (negative)
F The carry flag is set if there was a collision
Find the cell and its rectangle list.
CheckWallsVerticalFirst 57443 CALL FindPositionInCell Call FindPositionInCell.
Find the list of rectangles for the tile.
57446 LD BC,25396 Point BC at RectangleListTable.
57449 CALL GetTableEntry Call GetTableEntry.
57452 PUSH HL Copy the rectangle list to IY (using the stack).
57453 POP IY
Test the next rectangle.
CheckWallsVerticalFirst_Loop 57455 LD A,(IY+0) Return if this is the end of the list.
57458 AND A
57459 RET Z
Jump to CheckWallsVerticalFirst_Next if the object is not touching the rectangle.
57460 CALL CheckOverlapAlongY Call CheckOverlapAlongY.
57463 JR NC,CheckWallsVerticalFirst_Next Jump to CheckWallsVerticalFirst_Next if the object is not touching the rectangle.
Return if the object is touching the rectangle.
57465 CALL CheckOverlapAlongX Call CheckOverlapAlongX.
57468 RET C Return if the object is touching the rectangle.
Move on to the next rectangle.
CheckWallsVerticalFirst_Next 57469 INC IY Move on to the next rectangle.
57471 INC IY
57473 INC IY
57475 INC IY
57477 JR CheckWallsVerticalFirst_Loop Jump to CheckWallsVerticalFirst_Loop.
View the equivalent code in;
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