Drawing pixels: yLookupHi

       Name: yLookupHi                                               [Show more]
       Type: Variable
   Category: Drawing pixels
    Summary: Lookup table for converting pixel y-coordinate to high byte of
             screen address
    Context: See this variable in context in the source code
 References: This variable is used as follows:
             * GetScreenAddress uses yLookupHi


 This table returns the high byte of the screen address of the start of the
 row, for the custom screen mode.

 Note that the custom screen mode starts at address &5A80, so the first two
 entries in this table do not point to screen memory; the first two character
 rows in this table are off the top of the custom screen, so the first row
 on-screen is the third row. This is why, when we print the top two lines of
 text in the custom screen with the PrintCharacter routine, we do so at the
 following y-coordinates:

   * yCursor = 24 for the first line of text

   * yCursor = 33 for the second line of text

 To see where these are on-screen, we need to subtract 16 for the first two
 character rows which are off the top of the screen, to give:

   * y-coordinate = 8 for the first line of text

   * y-coordinate = 17 for the second line of text

 The value passed to PrintCharacter points to the bottom row of the character
 to print, so the first coordinate points to the ninth pixel row (as the first
 pixel row is row 0), and the second points to the 18th pixel row. There are
 eight pixels in each character row, so this prints the first row of text so
 that it has a one-pixel margin between the top of the text and the top of the
 screen, and it prints the second row so that it has a one-pixel margin between
 the top of the text and the bottom of the line above.

 I don't know why this table starts at &5800 and not &5A80, but that's how it
 is.


.yLookupHi

 FOR I%, 0, 31

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

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