Supporting dx, dy arrays

Applications can support dx, dy positioning of glyphs if they are running on Windows NT5 and using USP and/or RichEdit 3.0 to create and position the glyph string.

ExtTextOut does not support delta y positioning on Windows NT4, Windows 98, or Windows 95. Applications running on these platforms must call ExtTextOut multiple times in order to support dx, dy positioning arrays, as follows:

1. Use the OTLS to produce the glyph string from character string.
2. Use the OTLS to obtain the advance width information for each glyph.
3. Create a buffer containing only glyphs with the same delta y value (say, dy1). Replace glyphs having other delta y values with placeholders of the associated advance widths.
4. Call ExtTextOut to position the glyphs with the same delta y (dy1).
5. Replace appropriate placeholders with next group of glyphs, all of which have the same delta y (say, dy2).
6. Call ExtTextOut to position the glyphs with the same delta y (dy2).
7. Replace appropriate placeholders with next group of glyphs, all of which have the same delta y (say, dy3).
8. Call ExtTextOut to position the glyphs with the same delta y (dy3).
9. Continue replacing placeholders and calling ExtTextOut for each group of glyphs with discrete delta y values.

This process is illustrated in the diagram below.

Making multiple ExtTextOutcalls to perform dy positioning on systems without dx, dy support: