Drawing the screen: SCTBX2

       Name: SCTBX2                                                  [Show more]
       Type: Variable
   Category: Drawing the screen
    Summary: Lookup table for converting a pixel x-coordinate to the byte
             number in the pixel row that corresponds to this pixel
    Context: See this variable in context in the source code
 References: This variable is used as follows:
             * CPIX uses SCTBX2
             * HLOIN uses SCTBX2
             * letter2 uses SCTBX2
             * LOIN (Part 2 of 7) uses SCTBX2
             * LOIN (Part 5 of 7) uses SCTBX2
             * PIXEL uses SCTBX2


 The SCTBX1 and SCTBX2 tables can be used to convert a pixel x-coordinate into
 the byte number and bit number within that byte of the pixel in screen memory.

 Given a pixel x-coordinate X in the range 0 to 255, the tables split this into
 factors of 7, as follows:

   X = (7 * SCTBX2,X) + SCTBX1,X - 8

 Because each byte in screen memory contains seven pixels, this means SCTBX2,X
 is the byte number on the pixel row. And because the seven pixel bits inside
 that byte are ordered on-screen as bit 0, then bit 1, then bit 2 up to bit 6,
 SCTBX1,X is the bit number within that byte.


.SCTBX2

FOR I%, 0, 255

 EQUB (I% + 8) DIV 7

NEXT