Windows Power-User Series
Have you ever looked at some old
DOS documents with graphics or special characters and wished you could
see them as intended in a Windows program rather than having to open it in
an old DOS Editor using a DOS-window? You could use the OEM font set which
comes close to the view you'd see in a full-size DOS window. But Notepad is
stuck with ONLY ONE font, and many other Windows programs don't allow you to
use the OEM font either!
Well, by changing the value of one byte in Notepad, you can display a file in one of five new fonts; including the OEM font shown here:
Notepad actually uses some code from a
Windows system program called GDI32.DLL to set up how it will display the
contents of any file it opens. The particular API (Application
Program Interface) instruction we need to identify in the code
is called GetStockObject. When Notepad calls upon GDI32 to run
this specific instruction, it must also send a parameter (or argument) which
tells it what font to use. Notepad passes the data to GDI32 by first
placing it in a specific location of an area of memory known to the program
as The Stack; we say it pushes the data onto the stack. And,
logically enough, we'll be looking for a PUSH instruction just before the
CALL to the GDI32 code. Unless you want to try your hand at using whatever
sophisticated Windows debugging program you might have, then don't
worry about these details!! It makes sense (and turns out to be true) that
there'd be only one reference to GDI32.GetStockObject in the Notepad code,
and for a Windows 95 'B' machine, it will look like this once the code is
loaded into memory:
004027BE 6A10 push 00000010
004027C0 FF1594724000 Call dword ptr 
Here are some notes (only the details pertaining to fonts shown here) from a reference work on Windows API code [My own comments in brackets]:
The GetStockObject function retrieves a handle to one of the predefined stock pens, brushes, fonts, or palettes. HGDIOBJ GetStockObject( int fnObject // type of stock object ); Parameters fnObject -- Specifies the type of stock object. This parameter can be any one of the following values [only the fonts shown above will be listed here]: Value Meaning SYSTEM_FIXED_FONT Fixed-pitch (monospace) system font already used [ 16 = 10h ] in Windows versions earlier than 3.0 [This is the font used by NOTEPAD. Note the hex byte 10 that's pushed onto the stack just before the call.] OEM_FIXED_FONT Original equipment manufacturer (OEM) dependent [ 10 = 0Ah ] fixed-pitch (monospace) font. [This gives us an acceptable approximation in Windows programs to the old DOS font characters on most systems.] ANSI_FIXED_FONT Windows fixed-pitch (monospace) system font. [ 11 = 0Bh ] [Might be a nice alternative to the original font.] ANSI_VAR_FONT Windows variable-pitch (proportional space) system [ 12 = 0Ch ] font. [Sure looks tiny; although this might be very useful if you had huge text files to search!] DEVICE_DEFAULT_FONT "Windows NT only: Device-dependent font." [I'm not [ 14 = 0Eh ] exactly sure what this means, but from the pictures above you might conclude that using the 0Eh byte in Windows 95 simply displays the ANSI_FIXED_FONT with a larger size.] SYSTEM_FONT System font. By default, Windows uses the system [ 13 = 0Dh ] font to draw menus, dialog box controls, and text. In Windows versions 3.0 and later, the system font is a proportionally spaced font; earlier versions of Windows used a monospace system font. [ NOTE: By trying many different byte values, I came to the conclusion that using any value not defined on this list produces the same effect as using this font.]
After searching for the string of hex
digits which makes up the two instructions shown above (6A 10 FF 15 94 72 40 00) and verifying that
they occur only once in the file, I identified what I've been calling the
font byte (10h in the PUSH instruction) as offset location
001BBF for my copy of
NOTEPAD.EXE (08-24-96 11:11a 34,304 bytes).
If you have Windows 95 B and know how to use a hex editor (see the section titled, Making the changes to Notepad Yourself on my page about Removing the 'Nag Screen' if you need a free hex editor and some help using it), then you've already got all the info you need... Just load a COPY of NOTEPAD.EXE into your hex editor and go for it.
For those of you with Win 98, 98SE or NT I'd like to verify my findings before releasing them publicly; but feel free to ask for the information if you want to try it out! (Use: this online form to contact me.) I still need to search through a copy of Win NT's NOTEPAD.
NOTE: Since Notepad isn't very large (roughly 30kb) you might want to make a couple different versions saved under different names for whenever you might need them: NOTEANSI.exe or NOTEPOEM.exe (at least until I can make a menu program for choosing these fonts from within Notepad). Also: Notepad appears to run OK from any folder, even a different drive, at least on my Win 95 B machine, so you could place these patched copies in separate folders.
Tuesday August 22, 2000
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