Viewport: Exposing SetNextWindowViewport(). Used in demo and old/obsolete SetNextWindowPosCenter() (which is an interesting case). Fixed back-end likely crash calling GetFocus() after viewport destruction. Fixed metrics crash.

Viewport, Platform: Refresh monitor list (win32, glfw) + avoid calling GetWindowFocus before platform window creation to not require of backend to null-check things inconsistently. (#1542)

Viewport: Removed unnecessary fields (now that the coordinate system is consistent accross viewports): MouseRefPrevViewport, MouseClickedPosViewportId. (#1542)

Viewport, Platform: Using Platform_GetWindowFocus to provide a much stronger heuristic of platform z-order, in replacement for when the back-end cannot provide io.MouseHoveredViewport. The pressure for it to work well increased with the use of viewports by popups/menus. (#1542)

Viewport: Moved ScaleWindow* code in a proper location. Various comments.

Misc: tweaks + minor changes merged from master to reduce branch drift. Removed code that ended up unused.

Merge branch 'master' into viewport ...

# Conflicts:
#	imgui.cpp
#	imgui.h
#	imgui_internal.h

Misc: Stop moving window if mouse position becomes invalid. Flagged menus are _NoMove for sanity.

Misc: NavCalcPreferredRefPos selects between mouse and nav reference position + added sanity assert (merged from viewport branch to minimize branch drift).

Begin: Shuffled some code, _should_ have no side-effect. Clear NextWindowData in one call and more consistently. (merged from viewport branch to minimize branch drift).

Misc: Comments and shallow/small changes (merged from viewport branch to minimize branch drift).

ImGuiTextBuffer::appendfv needs to va_end the args_copy.

Viewport: Avoid creating viewport on drag (fix cc882b0)

Merge branch 'master' into viewport ...

# Conflicts:
#	examples/allegro5_example/imgui_impl_a5.cpp
#	examples/allegro5_example/imgui_impl_a5.h
#	examples/allegro5_example/imgui_impl_allegro5.cpp
#	examples/allegro5_example/imgui_impl_allegro5.h
#	examples/allegro5_example/main.cpp
#	examples/imgui_impl_allegro5.cpp
#	examples/imgui_impl_allegro5.h
#	imgui.cpp
#	imgui_internal.h

Internals: Removed unecessary Pos/PosFloat separation, only reason appears to be mostly pre-1.0. The only piece of code that I expected sub-pixel window position to matter actually already round its delta (wrongly so, will fix later/separately if we want).

Viewport: Tidying up AddUpdateViewport() calls. Moved flags argument. Removed extraneous mid-frame call to FindPlatformMonitorFromRect(). (#1542)

Viewport: Fixed glitches with newly appearing menus creating viewport while the underlying imgui window should be hidden. (#1542)

Viewport: Fixed issues with popups drifting in particular when reference mouse position become invalid (e.g. changing app focus while viewported-menu is open). Storing monitor index in viewport at beginning of the frame. (#1542)

Fix various typos.

Viewport: Fixed mouse hover flicker on mouse button release frame after moving a window. (#1542) ...

Platform: Clarifying some comments in back-ends.

Removed presumably obsolete MovingWindow tests which prevent move/merge logic in viewport branch from working in all situations (e.g. docking away when ActiveId is the ID of a tab)

Removed presumably obsolete MovingWindow tests which prevent move/merge logic in viewport branch from working in all situations (e.g. docking away when ActiveId is the ID of a tab)

Internals: Removed misleading ImRect::FixInverted + fix minor formatting in Readme. ...

Demo: Fixed Overlay: Added a context menu item to enable freely moving the window.

Viewport, Platform: Fixed IME positioning for multi-viewport. Moved API from ImGuiIO to ImGuiPlatformIO. Because it is extremely unlikely to people redefined this API manually the moving-forward-breakage is ok. (#1542) ...

SDL2 ime support under Win32 never worked properly because of SDL interferences.

Viewport: Clamp windows within monitors + fallback rescue window when it is out of sight (e.g. removed monitor, changed resolution) + Win32: declare primary monitor at the beginning of the list. (#1542)

Viewports: Todos, Tooltips/menus not automatically forced into their own viewport when the NoMerge flag is set (however the multiplication of viewports makes them more likely to protude and create their own). Win32: try to make primary monitor the first tin the list. (#1542)

Viewport: Added ImGuiConfigFlags_ViewportsNoMerge flag (to enforce a platform window for all floating windows) + minor tidying up and addition of non-functional wip code.

Window: Relaxed the internal stack size checker to allow Push/Begin/Pop/.../End patterns to be used with PushStyleColor, PushStyleVar, PushFont without causing a false positive assert. (#1767)

Viewport: Fixed initial popup positioning not using the monitor area properly. (#1542)

Viewport, Platform: Added work area in ImGuiPlatformMonitor. Renamed fields. (#1542)