I've been toying with DPI handling recently. Part of this is motivated by the work on Multiple Viewport #1542 which are making this topic trickier than it already was before. Some (early and experimental) commits are being pushed to the Viewport branch.

This is mostly a thread to link commits too, write down some notes and eventually attract feedback, suggestion or solutions.

The work involve

• imgui-side changes (how does it affects fonts? style? various sizes and positions)
• platform-side work

Single viewport DPI handling can be handled by the application at the moment (by using a larger font and scaling e.g. the style appropriately), however we ought to clarify and simplify the work that needs to be done, and support it in the examples. The position/size of windows relative to their viewport also ideally ought to be scaled.

Multi viewport DPI handling involve changing those depending on where we are located: moving an imgui window from screen 1 to screen 2 can affect sizing. Effectively calling Begin() can put you in a different DPI context. It's trickier to solve because e.g. our font system currently don't allow for arbitrary quality scaling so we may have to come up with scheme to make that more transparent eventually. Likewise for style (and scaling style sizes is a lossy operation).

Platform-side: At the moment I am focusing on Windows. I imagine (hope) MacOS will be easier but I don't have reliable access to a Mac right now. I don't know about Linux. The platform dependent part of the work is not very complex. Under Windows, consideration of backward compatibility with older versions of Windows and Windows SDK makes the code more messy, but nothing really hard.