This webpage tests whether the font rendering gamma is correct. This only works if the rendering engine uses anti-aliasing and also should be performed in the pixel-perfect 100% zoom.

Here are the four parts:
Test:
!!!!!!!!!!!!""""""""""""
!!!!!!!!!!!!""""""""""""
!!!!!!!!!!!!""""""""""""
!!!!!!!!!!!!""""""""""""
!!!!!!!!!!!!""""""""""""
!!!!!!!!!!!!""""""""""""


The result should look something like this (minor artifacts between the characters and the shade of gray being slightly off are acceptable, the shade of gray being visually distinct is a FAIL):


Classic GDI passes the test:


In ClearType GDI, there is a gamma setting: cleartypeGDI-gamma.PNG it turns out that out of the six options only the last one passes the test:







Chromium 79.0.3912.0 (Developer Build) (64-bit) on Microsoft Windows always fails whether the system rendering engine is set to classic GDI (top) or ClearType GDI (bottom):



Android Chrome 42.0.2311.111 fails:


In Firefox, it is complicated. In the default settings if the system is set to classic GDI it fails:

and if the system is set to ClearType GDI it also fails:

However, if gfx.font_rendering.cleartype_params.rendering_mode is set to 2 and the system is set to ClearType GDI, it barely passes:

And if gfx.canvas.azure.backends and gfx.content.azure.backends are changed from direct2d1.1,skia,cairo to direct2d1.1,cairo and hardware acceleration is disabled it properly uses GDI (of which the results are mentioned above) but only in older versions. https://support.mozilla.org/en-US/questions/1268750
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