Programmatically enable ClearType in Windows Mobile

Question

For our Windows Mobile application I want to enable the ClearType option on the device. According to this article on MSDN it should be done be setting the following registry key:

HKEY_LOCAL_MACHINE\SYSTEM\GDI\Cleartype

But nothing happens after setting this particular key. Even a soft reset does not enable it, but simply gets rid of the registry key I just created.

Strange thing is that when I set it manually using Settings->System->Screen->ClearType it works immediately. And comparing the registry exports before and after changing the setting show that it is just the key mentioned above that changes.

I don't quite understand why it wouldn't work when I change the registry key myself. Anyone who knows what I'm doing wrong here?

[update] It looks like the solution is to do either:

• Broadcast a WM_SETTINGCHANGE message with the correct parameters like:

  SendMessage(HWND_BROADCAST, WM_SETTINGCHANGE, 0, 1)

  But that has not worked so far. I guess the wParam parameter might need a different value.

• Or call CreateEvent with the relevant event for ClearType changes. A bit like BacklightChangeEvent or SDKBacklightChangeEvent would work. But so far I haven't seen any documentation on these events, so I can't work out what the event would be.

Answer 1

Did you flush the registry after changing the value and before doing the Soft Reset?
Sounds like the change did not persist.

Answer 2

I have found the solution myself. It turns out that making the registry change is not needed, but just a call to SystemParametersInfo with the SPI_SETFONTSMOOTHING parameter is enough to make it apply the changes.

This is my code using .NET CF 2.0:

[DllImport("coredll.dll", SetLastError = true)]
static extern bool SystemParametersInfo(uint uiAction, uint uiParam, ref int pvParam, uint fWinIni);

const uint SPI_SETFONTSMOOTHING = 0x004b;
const uint SPI_UPDATEINI = 0x1;

int pv = 0;
bool ret = SystemParametersInfo(SPI_SETFONTSMOOTHING, 1, ref pv, SPIF_UPDATEINIFILE);