Display of Asian characters (with Unicode): Difference in character spacing when presented in a RichEdit control compared with using ExtTextOut

This picture illustrates my predicament:

All of the characters appear to be the same size, but the space between them is different when presented in a RichEdit control compared with when I use ExtTextOut.

I would like to present the characters the same as in the RichEdit control (ideally), in order to preserve wrap positions.

Can anyone tell me:

a) Which is the more correct representation?

b) Why the RichEdit control displays the text with no gaps between the Asian Characters?

c) Is there any way to make ExtTextOut reproduce the behaviour of the RichEdit control when drawing these characters?

d) Would this be any different if I was working on an Asian version of Windows?

Perhaps I'm being optimistic, but if anyone has any hints to offer, I'd be very interested to hear.

In case it helps:

Here's my text:

快的棕色狐狸跳在懶惰狗1 2 3 4 5 6 7 8 9 0

apologies to Asian readers, this is merely for testing our Unicode implemetation and I don't even know what language the characters are taken from, let alone whether they mean anything

In order to view the effect by pasting these characters into a RichEdit control (eg. Wordpad), you may find you have to swipe them and set the fo开发者_高级运维nt to 'Arial'.

The rich text that I obtain is:

{\rtf1\ansi\ansicpg1252\deff0\deflang2057{\fonttbl{\f0\fnil\fcharset0 Arial;}}{\colortbl ;\red0\green0\blue0;}\viewkind4\uc1\pard\sa200\sl276\slmult1\lang9\fs22\u24555?\u30340?\u26837?\u33394?\u29392?\u29432?\u36339?\u22312?\u25078?\u24816?\u29399?1 2 3 4 5 6 7 8 9 0\par\pard\'a3 $$ \'80\'80\cf1\lang2057\fs16\par}

It doesn't appear to contain a value for character 'pitch' which was my first thought.

I don't know the answer, but there are several things to suspect:

• There are several versions of the rich edit control. Perhaps you're using an older one that doesn't have all the latest typographic improvements.
• There are many styles and flags that affect the behavior of a rich editcontrol, so you might want to explore which ones are set and what they do. For example, look at EM_GETEDITSTYLE.
• Many Asian fonts come in two versions on Windows. One is optimized for horizontal layout, and the other for vertical layout. That latter usually has the same name, but has @ prepended to it. Perhaps you are using the wrong one in the rich edit control.

UPDATE: By messing around with Wordpad, I was able to reproduce the problem with the crowded text in the rich edit control.

1. Open a new document in Wordpad on Windows 7. Note that the selected font is Calibri.
2. Paste the sample text into the document.
3. Text appears correct, but Wordpad changed the font to SimSun.
4. Select the text and change the font back to Calibri or Arial.

The text will now be overcrowded, very similar to your example. Thus it appears the fundamental problem is with font linking and fallback. ExtTextOut is probably selecting an appropriate font for the script automatically. Your challenge is to figure out how to identify the right font for the script and set that font in the rich edit control.

This will only help with part of your problem, but there is a way to draw text to a DC that will look exactly the same as it does with RichEdit: what's called the windowless RichEdit control. It not exactly easy to use: I wrote a CodeProject article on it a few years back. I used this to solve the problem of a scrollable display of blocks of text, each one of which can be edited by clicking on it: the normal drawing is done with the windowless RichEdit, and the editing by showing a "real" RichEdit control on the top of it.

That would at least get you the text looking the same in both cases, though unfortunately both cases would show too little character spacing.

One further thought: if you could rely on Microsoft Office being installed, you could also try later versions of RichEdit that come with office. There's more about these on Murray Sargent's blog, as well as some interesting articles on font binding that might also help.

ExtTextOut allows you to specify the logical spacing between records. It has the parameter lpDx which is a const pointer to an array of values that indicate the distance between origins of adjacent character cells. The Microsoft API documentation notes that if you don't set it, then it sets it's own default spacing. I would have to say that's why ExtTextOut is working fine.

In particular, when you construct a EMR_EXTTEXTOUTW record in EMF, it populates an EMR_TEXT structure with this DX array - which looking at one of your comments, allowed the RichEdit to insert the EMF with the information contained in the record, whereby if you didn't set a font binding then the RTF record does some matching to work out what font to use.

In terms of the RichEdit control, the following article might be useful:

Use Font Binding in a Rich Edit Control

After character sets are assigned, Rich Edit scans the text around the insertion point forward and backward to find the nearest fonts that have been used for the character sets. If no font is found for a character set, Rich Edit uses the font chosen by the client for that character set. If the client hasn't specified a font for the character set, Rich Edit uses the default font for that character set. If the client wants some other font, the client can always change it, but this approach will work most of the time. The current default font choices are based on the following table. Note that the default fonts are set per-process, and there are separate lists for UI usage and for non-UI usage.

If you haven't set the characterset, then it further explains that it falls back to ANSI_CHARSET. However, it's most definitely a lot more complicated than that, as that blog article by Murray Sargent (a programmer at Microsoft) shows.