For the purpose of automated regression testing, I am capturing some screenshots of a GDI canvas inside our application and compare them against screenshots taken from new builds. The image comparison has to be pixel perfect for the test to pass. This works well on my machine and on a colleague's machine (both Windows 7) but if we compare the images taken on one machine with those from another the comparison always fails. The differencing shows some minor differences in GDI font rendering. I would like to find out which factors could affect the font rendering that cause this difference in appearance and am running out of ideas.
- We have the same fonts installed as far as we are aware.
- Font size is set to 100 % on both machines
- We're running on the same screen resolution
- I suspected ClearType settings and indeed checking the registry HKCU\Software\Microsoft\Avalon.Graphics\DISPLAY1 showed up with some keys set for level, contrast and text contrast on my machine and these keys missing for my colleague. But I removed the keys from my registry and after a reboot we still don't produce matching images. Is there another way to export clear type settings?
- I also tried Visual Effects / Smooth Edges of screen fonts to no avail
Are there any other settings that could cause the font rendering coming out differently? Or are there any service packs, in particulr that could affect it?