Drawing pixels: yLookupLo

       Name: yLookupLo                                               [Show more]
       Type: Variable
   Category: Drawing pixels
    Summary: Lookup table for converting pixel y-coordinate to low byte of
             screen address
    Context: See this variable in context in the source code
 References: This variable is used as follows:
             * DrawDashboardLine uses yLookupLo
             * DrawObjectEdge (Part 3 of 5) uses yLookupLo
             * GetScreenAddress uses yLookupLo


 For character rows 0 to 7 and 16 to 31, this table returns the low byte of
 the screen address of the start of the row, for the custom screen mode.

 For character rows 8 to 15, the table is reused, as these locations would
 point to the blue sky, and we don't draw in the sky as it contains working
 game code. Instead, the lookup table at yLookupLo+8 contains pixel masks for
 use in the line-drawing routine at DrawDashboardLine.


.yLookupLo

 FOR I%, 0, 7

  EQUB LO(&5800 + (I% * &140))

 NEXT

 EQUB %01110111         \ Clear the first pixel of a mode 5 pixel byte
 EQUB %10111011         \ Clear the second pixel of a mode 5 pixel byte
 EQUB %11011101         \ Clear the third pixel of a mode 5 pixel byte
 EQUB %11101110         \ Clear the fourth pixel of a mode 5 pixel byte

 EQUB %01110111         \ Clear the first pixel of a mode 5 pixel byte
 EQUB %10111011         \ Clear the second pixel of a mode 5 pixel byte
 EQUB %11011101         \ Clear the third pixel of a mode 5 pixel byte
 EQUB %11101110         \ Clear the fourth pixel of a mode 5 pixel byte

 FOR I%, 16, 31

  EQUB LO(&5800 + (I% * &140))

 NEXT

 EQUB &81, &81          \ These bytes appear to be unused
 EQUB &81, &81
 EQUB &81, &81
 EQUB &81