When Windows system fonts change shape and font smoothing drops out, note the state of the smoothing checkbox first. In field reports of legacy HMI programming tools, the change appears while a project loads, holds until the next reboot, and leaves no saved setting behind. Run the launch, load and reboot test to confirm which kind you have, then treat it as a session cost or restore the saved settings.
Opening a project in legacy HMI programming software can flip the Windows system fonts to a different face and switch font smoothing off, with no setting touched. The pattern that shows up in field reports is narrow: the software starts clean, the change lands while the project file loads, and one reboot brings the old look back. That combination means the change lives in the running Windows session only. This article gives you the test that confirms it in one pass, the symptoms that point somewhere else, and the action for each result, on Windows 2000, XP and Vista.
Symptoms and what each one points to
Match what you see to one of these before changing anything.
- Fonts change while a project loads. System menu and title bar text switch face, and the font smoothing checkbox clears. This is the session-only change the rest of the article covers.
- Fonts change at software start, with no project loaded. A different trigger. Record the software version and the Windows edition and hand both to the vendor; the reported behavior starts at project load.
- The change is still there after a reboot. Windows has saved a display setting. Go to the restore step, not the reboot step.
- A warning about the DPI setting appears at every software start. Reported alongside the font change on a system running a custom DPI size. Cancel it at each start; the reports name no way to silence it.
- Fonts went wrong right after an install round that also touched the browser. Too many variables changed in one session. Skip the reinstalls and run the load test below.
Text that is clipped at the dialog edge is a separate rendering fault, not a restyled system font; the article on HMI dialogs clipped by legacy Windows fonts covers that one.
Record the baseline first
On Windows 2000 and XP the smoothing setting sits at Display Properties, Appearance tab, Effects button, checkbox Use the following method to smooth edges of screen fonts, with Standard or ClearType selected. On Vista the same controls sit under Personalization in Control Panel. ClearType is the smoothing Windows draws for LCD flat panels; Standard suits CRT tubes.
Write down three things before you touch the software:
- Which smoothing method the checkbox shows.
- The Windows edition.
- The DPI size. Windows' normal size is 96 DPI and its Large preset is 120 DPI; a custom size prints as a percentage of the normal size.
Those three values let support reproduce what you see on the same screen.
The launch, load, reboot test
- Note the baseline: smoothing method, checkbox state, Windows edition, DPI size.
- Start the software from the Start menu and open no project. Compare the fonts and the checkbox against the baseline.
- If step 2 is clean, open a project from the file menu and watch the system fonts and the smoothing checkbox while the file loads. If the current look must stay intact for something else on screen, cancel the open dialog instead; the reports show cancelling leaves the settings untouched.
- Save other work and reboot once. Compare the fonts and the checkbox with the baseline again.
- Read the result. Change only at load, gone after reboot: the session-only change. Change at start with no project, or a change that survives reboot: a different fault, with its own path below.
Scenario: a Windows XP programming PC at 134% DPI
Inputs, and where each comes from: font smoothing ClearType, checkbox ticked at the Display Properties path (the report's baseline); Windows XP (reported); a custom DPI size of 134% (reported on a second system that showed the same behavior); the software starts clean from the Start menu (reported).
Rule in words: a session-only display change carries three marks together. Launching the software alone leaves the baseline in place. The change appears while a project loads. One reboot restores the baseline. Any other order is a different fault.
Arithmetic: the custom size converts to DPI as 134% × 96 DPI = 128.64 DPI, so about 129 DPI. The Large preset works out at 120 ÷ 96 DPI = 125% of normal. This system therefore ran 129 − 120 = 9 DPI above Large, about 7% larger again. That is the kind of detail worth writing down, because support reproducing the fault needs the same numbers on the same screen.
Result: start clean, checkbox ticked, fonts normal. Project load: system menu font changed, checkbox cleared. One reboot: fonts back to normal, checkbox ticked again.
Decision: that is the session-only branch. Treat the change as a cost of the programming session: load projects when a reboot can follow, and cancel the open dialog when the screen must stay untouched. The threshold for leaving this branch: any font change at start with no project loaded, or any change that survives reboot. Either one goes to the restore and escalate steps below.
What to do in each branch
Session-only. No report names a software setting that stops the change, so plan around it. Put a reboot at the end of the programming block, or cancel the open dialog when the current screen matters. Leave the installation alone: one Vista report mixed an uninstall with browser upgrades and a reinstall in the same week, so the recovery there cannot be pinned on any single step.
Change survives reboot. Use Windows' own restore: Control Panel, Appearance and Personalization, Fonts, Font settings, Restore default font settings. If the change comes back on the next project load, the saved settings are being touched after all; record the baseline values again and hand them to the vendor.
Change at start, no project loaded. Escalate with the recorded software version, Windows edition, smoothing method and DPI size. Keep the one-change-at-a-time discipline there; it is the same method that isolates a startup DLL crash in HMI software that crashes at startup.
If the programming PC is a newer Windows machine, compatibility mode is a separate question with its own setup; the article on running legacy HMI programming software in XP compatibility mode covers that side.
Recommendation
Recommendation: run the launch, load, reboot test against a recorded baseline before changing any Windows setting. If fonts change only while a project loads and one reboot restores them, treat it as a session cost of the tool: schedule project loads so a reboot can follow, cancel the open dialog when the screen must stay untouched, and keep the software installed. If the change appears at launch or survives reboot, stop testing, use the restore default font settings action, and send the vendor the smoothing method, Windows edition and DPI size you recorded.
Questions
Does this font change affect saved projects or Windows settings?
No saved setting changes. The reports show the checkbox and fonts back at their baseline after one reboot, so projects, files and Windows configuration are untouched. The change lives in the running session only. That is why the test compares the checkbox before the load and after the reboot: that comparison is what tells you the saved values never moved.
Why does a DPI warning appear each time the software starts?
The report that documents the font change also complains about a warning over the DPI setting at every start. The system behind it ran a custom DPI size, and the routine was to cancel the warning each time. No report names a setting that silences it. If the custom size exists for readability, keep it and cancel the warning; if not, set one of the 96 DPI or 120 DPI presets Windows offers.
Should I uninstall the HMI software to get the fonts back?
One early report saw fonts return after an uninstall, but the same stretch included browser upgrades, a downgrade and a reinstall, so no single step there can take the credit. Later reports tie the change to project loading, not to the installation, and show one reboot restoring the fonts. Keep the software installed and run the launch, load, reboot test instead.
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