Screen buffer: DrawTrackBytes (Part 1 of 3)

       Name: DrawTrackBytes (Part 1 of 3)                            [Show more]
       Type: Subroutine
   Category: Screen buffer
    Summary: Draw the pixel bytes that make up the track view (0 to 15)
  Deep dive: Drawing around the dashboard
             Drawing the track view
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * DrawTrackView (Part 2 of 4) calls DrawTrackBytes
             * DrawTrackView (Part 3 of 4) calls DrawTrackBytes
             * DrawTrackView (Part 4 of 4) calls DrawTrackBytes


 This routine draws pixel bytes 0 to 39, which draws a one-pixel high line in
 the track view.

 Note that this routine starts on a page boundary (DrawTrackBytes = &7C00).
 This is important as it means the code can be modified at a specific address
 using only the low byte of that address, as we know that high byte is the same
 throughout the routine. This is why the staDrawByte and ldaDrawByte lookup
 tables only need to store the low bytes of the addresses for instructions that
 we need to modify.


.DrawTrackBytes

 DRAW_BYTE 0            \ Draw pixel bytes 0 to 15
 DRAW_BYTE 1
 DRAW_BYTE 2
 DRAW_BYTE 3
 DRAW_BYTE 4
 DRAW_BYTE 5
 DRAW_BYTE 6
 DRAW_BYTE 7
 DRAW_BYTE 8
 DRAW_BYTE 9
 DRAW_BYTE 10
 DRAW_BYTE 11
 DRAW_BYTE 12
 DRAW_BYTE 13
 DRAW_BYTE 14
 DRAW_BYTE 15

 JMP byte1              \ Jump to part 2 to continue with pixel byte 16