Blurry fonts after font size change

Hi,

My fonts are blurry after trying to select a custom DPI then resetting the DPI to 120, BUT ONLY IN CERTAIN SITUATIONS!!

It seems to be older applications that are affected.

For example, here is the difference between the rendering of courier new 30 point in mirc (popular irc client) and MS Word:

[see image here: h.imagehost.org/0995/G2.png (word is at the bottom).]

This is just one example. It seems half the apps have the blurred version of the font and half have the sharp version.

I should state now, that I have deliberately chosen courier new, but even if I choose other fonts, they are still blurred. Also, cleartype is switched on. If I switch to the windows vista basic scheme, the problem disappears; when I switch back to aero, the problem reappears. Cleartype is switched on in both cases. If I switch cleartype off *everything* looks horrible and jagged. The MS Cleartype tuner is of no help.


Thanks in advance for your help.

OK, since I found the solution I shall answer my own post.

When you right click the desktop, select personalise, then click "Adjust font size (DPI)", vista runs a program called dpiscaling.exe. This has two radio buttons for the "standard" settings - Default scale (96 DPI) and Larger Scale (120 DPI). There is a button for selecting a Custom DPI.

When you click the custom DPI button, there is a check box "Use Windows XP DPI scaling". If this is unchecked, you will end up with the blurred fonts I experienced even if you reselect one of the standard DPIs (96 or 120). This is extremely poor user interface practice from Microsoft - an option that is actually applicable to one of the standard DPIs is hidden in another dialog. [For those who are interested, dpiscaling.exe writes this option to the registry under this key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\DWM - there is a value UseDPIScaling which MUST BE ZERO if you want sharp fonts]

So, why does this apply only to certain applications? Well, under vista, applications can control the way vista scales their fonts by calling a function from the Win32 API: SetProcessDPIAware(). Windows applications developed using "modern" frameworks - e.g. with the .NET framework automatically call this function. Applications developed with older frameworks (older versions of MFC, WTL) or just directly using the win32 API do not call it.