Window border width does not respect system theme

[c0d3h4x0r]

Environment

Windows build number: 10.0.18362.207
Windows Terminal version (if applicable): 0.2.1831.0

Steps to reproduce

1. Install the third-party Aerolite.theme to get window borders back to being usable (i.e. not zero-width).
2. Note that Command Prompt, Windows PowerShell, and Ubuntu for Windows 10 command shell windows all respect the nice new border width.
3. Launch Windows Terminal.

Expected behavior

Windows Terminal should also respect the theme's window border width.

Actual behavior

Windows Terminal has a zero-width window border in defiance of the system theme, making it nearly impossible to resize.

[zadjii-msft]

Is there a way to change the width of the window borders without installing a third-party theme installer?

I'm going to guess that this is a subset of #1625, assuming that the border width is in fact a system theme property we can query

[c0d3h4x0r]

That’s the wrong question to ask. The right question is, if every other app seems able to honor the third-party theme, why won’t Windows Terminal?

[DHowett-MSFT]

Unfortunately, it is the right question to ask. There's a lot of history here for us to unravel, the earliest part of which is "why is it so hard to draw in the titlebar" and the latest part of which is "now that we're drawing in the titlebar, why was it decided by the win32 kernel driver and desktop window compositor that we absolutely must handle all of this ourselves? it's like this system was never actually designed but instead organically grown."

We're a fairly simple UI with fairly simple requirements, but one of those requirements is "have a custom color in our title bar." Unfortunately, that means:

• We need to draw the titlebar ourselves, in its entirety, which means:
• We need to have the UI framework (here Xaml Islands) go edge-to-edge, which means:
• we need to draw our own window borders
• we need to draw our own caption buttons
• we need to account for the theme part size of the window's elements
• we lose access to DWM shadows
  • dwm shadows are a trick, the window border is actually 8px wide and the compositor eats 7 pixels off the edge to make a shadow
  • when we try to draw our own title bar, dwm gives up and says "you don't want X? I'll take away Y, Z, A, B and C as well. Enjoy."
  • there's some weird magic hit testing that we cannot replicate for the resize handles "off the edge of the window"
• we need to cut a hole in the Xaml island to allow titlebar and drag input to come back through (yes, this is silly)
• we are driving dependencies on our internal partners to make this less of a heckscape.

I spent almost my entire sunday trying to answer all of the questions that arise from this list. It's not due to ignorance that we're asking the questions that we are.

[DHowett-MSFT]

Incidentally, the work merged in #929 does bring back theme-sized drag handles, they just look like a black hole opened up and consumed the contents of your display. ;)

Under all of the theming slapped down by the desktop compositor is actually just the Windows Vista Aero Basic theme with all of its rounded corners and weird thick window borders.

[c0d3h4x0r]

We're a fairly simple UI with fairly simple requirements, but one of those requirements is "have a custom color in our title bar."

And from that "requirement" stems the plethora of other problems. Instead, revisit that requirement -- why is it a requirement? Why does this app think it needs to be "more special" than other Windows applications and thus inconsistent with them (and likely less compatible with other system-wide UI changes that may come in future major Windows revisions)? Can the problem that "requirement" is trying to solve be better solved instead via some other design choice that avoids all the myriad technical issues created by the current approach?

[DHowett-MSFT]

This might be better with recent dev builds. We're giving DWM a lot more control over the window frame than we were prior.

[c0d3h4x0r]

That sounds like a wise approach to me. 👍