Routines
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D292: Test Left Column
Used by the routine at DrawTerrain.
Tests the right end of a segment of a tile in the left column against the horizontal position in B.
Input
B Horizontal position to test against
IX Address of the record of the segment
Output
F Zero if the end of the segment is at the position or beyond it
TestLeftColumn D292 LD A,($CE37) The vertical step.
D295 AND A Jump to TestLeftColumn_Sloped if A is not zero.
D296 JR NZ,TestLeftColumn_Sloped
D298 LD A,(IX+$00) Read offset 00 of IX.
D29B ADD A,(IX+$02) Add the byte at offset 02 of IX to A.
D29E JR TestLeftColumn_Compare Jump to TestLeftColumn_Compare.
TestLeftColumn_Sloped D2A0 LD A,($CE59) The horizontal step copy.
D2A3 AND A Jump to TestLeftColumn_Direction if A is not zero.
D2A4 JR NZ,TestLeftColumn_Direction
D2A6 LD A,($CE43) The segment column.
D2A9 ADD A,$08 Add 08 to A.
D2AB JR TestLeftColumn_Compare Jump to TestLeftColumn_Compare.
TestLeftColumn_Direction D2AD LD A,($E41B) The slope direction.
D2B0 CP $01 Jump to TestLeftColumn_Start if A is 01.
D2B2 JR Z,TestLeftColumn_Start
D2B4 LD A,(IX+$02) Read offset 02 of IX.
D2B7 JR TestLeftColumn_Compare Jump to TestLeftColumn_Compare.
TestLeftColumn_Start D2B9 LD A,(IX+$00) Read offset 00 of IX.
TestLeftColumn_Compare D2BC CP B Return if A is less than B.
D2BD RET C
D2BE XOR A Clear A.
D2BF RET Return.
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