fix: set_primary_window no longer breaks other windows

[v-ein]

---

name: Pull Request
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title: fix: set_primary_window no longer breaks other windows
assignees: ''

---

Description:

With this PR, set_primary_window no longer modifies windows other than the window passed in and the previous primary window (if it was set). This fixes #1691, effectively changing window position only when the window switches between primary and regular state. No other windows, in particular, popups and modals, are affected (keep in mind that a modal that has a non-empty label still won't center properly - see #2323 which is not fixed yet).

The only change set_primary_window still does to every window is re-focusing them - this is necessary to place the primary window to the bottom of Z-order. There are no public functions in ImGui API to control Z order, so re-focusing is the only way to place them atop of the primary window (so that they are not hidden behind). As a result, all windows after this call are always reordered according to their creation order. This matches behavior that existed before this PR.

Another change in this PR is that set_primary_window keeps window flags that are not related to positioning it as a primary window, for example, horizontal_scrollbar. This fixes #1978.

Also, the 2nd argument of set_primary_window is now optional, which allows for a more intuitive call like set_primary_window(wnd) rather than set_primary_window(wnd, True) (you know, I always hated to type that True 😂).

Concerning Areas:
If ImGui ever provides API to conrol windows' Z-order, we'll need to make use of it in place of refocusing every window.