Multiple viewports not merged if something has active focus. #4212
Description
Version/Branch of Dear ImGui:
Dear ImGui 1.80 (18000)
--------------------------------
sizeof(size_t): 8, sizeof(ImDrawIdx): 4, sizeof(ImDrawVert): 20
define: __cplusplus=199711
define: IMGUI_DISABLE_DEFAULT_ALLOCATORS
define: _WIN32
define: _WIN64
define: _MSC_VER=1928
define: _MSVC_LANG=201402
define: IMGUI_HAS_VIEWPORT
define: IMGUI_HAS_DOCK
--------------------------------
io.BackendPlatformName: Propeller
io.BackendRendererName: NULL
io.ConfigFlags: 0x00000441
NavEnableKeyboard
DockingEnable
ViewportsEnable
io.ConfigViewportsNoDecoration
io.ConfigDockingAlwaysTabBar
io.ConfigDockingTransparentPayload
io.ConfigInputTextCursorBlink
io.ConfigWindowsResizeFromEdges
io.ConfigMemoryCompactTimer = 60.0
io.BackendFlags: 0x00001C02
HasMouseCursors
PlatformHasViewports
HasMouseHoveredViewport
RendererHasViewports
--------------------------------
io.Fonts: 1 fonts, Flags: 0x00000000, TexSize: 512,64
io.DisplaySize: 1553.00,825.00
io.DisplayFramebufferScale: 1.00,1.00
--------------------------------
style.WindowPadding: 8.00,8.00
style.WindowBorderSize: 1.00
style.FramePadding: 4.00,3.00
style.FrameRounding: 0.00
style.FrameBorderSize: 1.00
style.ItemSpacing: 8.00,4.00
style.ItemInnerSpacing: 4.00,4.00
Back-end/Renderer/Compiler/OS
Back-ends: Custom backend on top of SDL2, Win32
Compiler: MSVC
Operating System: Windows 10
My Issue/Question:
I'm looking into issues in a work-in-progress game related to window resizing and platform window generation. I'm still narrowing things down, but I've found a weird behavior I believe is a bug. Viewports are only merged if g.ActiveId == 0:
Lines 11924 to 11928 in db0338a
I believe this intended to prevent a window from disappearing if it has focus, but since the ActiveId tracks global focus, windows are not merged. This seems wrong to me.
Standalone, minimal, complete and verifiable example:
This can be reproduced from the ImGui demo:
- Open the Log example and About Dear ImGui window.
- Drag the About Dear ImGui window to the side so that a new platform window is created.
- Click in the Filter textbox on the Log example so that it gains focus.
- Resize the parent window to be larger so that it now fully encompasses the About Dear ImGui window.
- Expect it to be absorbed into the parent viewport, but it is not.
- Click elsewhere to make the Filter textbox loses focus, and watch the About Dear ImGui get absorbed into the parent window.