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Client support issues
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 will have to call ExtTextOut multiple times in order to support dx, dy positioning arrays.
To support dx, dy arrays on Windows NT4, Windows 98, or Windows 95:
- Produce the glyph string from character string, using the OTLS.
- Obtain the advance width information for each glyph, using the OTLS.
- Create a buffer containing only glyphs with the same delta y value (say, dy1), and replace glyphs having other delta y values with place-holders of the associated advance widths.
- Call ExtTextOut to position the glyphs with the same delta y (dy1).
- Replace appropriate placeholders with next group of glyphs, all of which have the same delta y (say, dy2).
- Call ExtTextOut to position the glyphs with the same delta y (dy2).
- Replace appropriate placeholders with next group of glyphs, all of which have the same delta y (say, dy3).
- Call ExtTextOut to position the glyphs with the same delta y (dy3).
- 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:
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String of glyphs in glyph buffer |
| Delta-y values of glyphs |
dy0 |
dy1 |
dy0 |
dy0 |
dy2 |
dy1 |
dy2 |
dy0 |
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First Call to ExtTextOut |
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| Penpoint moved dy0 |
posit-ioned dy0 |
width place-holder |
posit-ioned dy0 |
posit-ioned dy0 |
width place-holder |
width place-holder |
width place-holder |
posit-ioned dy0 |
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1 |
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| Next Call to ExtTextOut |
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| Penpoint moved dy1 |
posit-ioned dy0 |
posit-ioned dy1 |
posit-ioned dy0 |
posit-ioned dy0 |
width place-holder |
posit-ioned dy1 |
width place-holder |
posit-ioned dy0 |
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| Next Call to ExtTextOut |
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| Penpoint moved dy2 |
posit-ioned dy0 |
posit-ioned dy1 |
posit-ioned dy0 |
posit-ioned dy0 |
posit-ioned dy2 |
posit-ioned dy1 |
posit-ioned dy2 |
posit-ioned dy0 |
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this page was last updated 27 November 2001
© 2001 Microsoft Corporation. All rights reserved. Terms of use.
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