CSS Pixels: Verify how density-independent pixels behave in Windows and Mac

[maryjom]

In June call (the 7th?) and other days we had discussions about CSS pixels, but we do need to understand better how density-independent pixels behave (if it's comparable to CSS pixels). This question also came up in the AG WG 3rd content review.

@mitchellevan I think you had checked Android (and iOS?) and it was comparable. Having this documented somewhere would be super-helpful.

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@mitchellevan's edit 2023-12-03: The scope of the present issue will be Windows and Mac. Specifically, the present issue will be our response to this part of @melaniephilipp's 2023-09-29 public comment on the FPWD, moved here from #227:

Do you have any guidance on how to measure the CSS pixel equivalents for macOS software [or] Window software ... for testing purposes?

[mitchellevan]

I added the "FPWD" label to the present issue because it will address a portion of #227.

[maryjom]

Specifics of "how to measure" density-independent pixels for Windows and Mac for testing depends on available measuring tools. In issue 227, mraccess said "There are pixel rules apps for some platforms like Android and Windows that display a pixel rule as an overlay on top of the software being tested - this likely would only work for open software and not closed software."

To me, it isn't up to WCAG2ICT to define or list those tools. We could simply mention that some platforms have available measurement tools.

I am not sure what "proof" or additional guidance readers of WCAG2ICT might be looking for. CSS pixels don't exist for non-web ICT software developers to use, so aren't truly meaningful in those contexts. Their "equivalent" or at least equivalent concept for software developers is in the platform-specific density-independent pixels, so that should be used.

For testing, it's a larger discussion that should occur outside of this TF - "What are the correct test techniques for non-web software?" is a valid question that should be answered. Our TF is not at liberty to specifically answer that, to develop those test techniques, or define the tools to be used.

[maryjom]

The answer to this is the same as the answer in issue #227.