Docking: how to figure out if a docked tab becomes active/visible?

[parbo]

Version/Branch of Dear ImGui:

Dear ImGui 1.84 WIP (18302)
--------------------------------
sizeof(size_t): 8, sizeof(ImDrawIdx): 2, sizeof(ImDrawVert): 20
define: __cplusplus=201703
define: _WIN32
define: _WIN64
define: _MSC_VER=1928
define: _MSVC_LANG=201703
define: IMGUI_HAS_VIEWPORT
define: IMGUI_HAS_DOCK
--------------------------------
io.BackendPlatformName: imgui_impl_glfw
io.BackendRendererName: imgui_impl_opengl3
io.ConfigFlags: 0x00000440
 DockingEnable
 ViewportsEnable
io.ConfigViewportsNoAutoMerge
io.ConfigViewportsNoDecoration
io.ConfigInputTextCursorBlink
io.ConfigWindowsResizeFromEdges
io.ConfigMemoryCompactTimer = 60,0
io.BackendFlags: 0x00001C06
 HasMouseCursors
 HasSetMousePos
 PlatformHasViewports
 HasMouseHoveredViewport
 RendererHasViewports
--------------------------------
io.Fonts: 7 fonts, Flags: 0x00000000, TexSize: 4096,4096
io.DisplaySize: 2560,00,1377,00
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: 0,00
style.ItemSpacing: 8,00,4,00
style.ItemInnerSpacing: 4,00,4,00

My Issue/Question:

In the docking branch, is there a way to figure out if a docked window (i.e. a tab) became active/visible? ImGui::IsWindowAppearing() does not seem to work for that.

[ocornut]

Hello,
Please define "active/visible" and why IsWindowAppearing() doesn't work for you.

[parbo]

When opening a window in a dockspace by calling ImGui::SetNextWindowDockId before ImGui::Begin, then ImGui::IsWindowAppearing doesn't return true. Also, I had expected that switching between tabs in a dockspace would ImGui::IsWindowAppearing to become true as the tab becomes active, but it doesn't afaict. And if that is intended, then I think there should be some other API to know that a docked window in a tab became visible.

[ocornut]

The reason I asked the question is that there are situations we may want a different appearing condition that the one you mention here, and specifically #2283 wants a different one and couldn't obtain it. And I assumed it was still the case.

But what I'm seeing right now after testing is that we "accidentally" solved #2283 but what you mention - which is the most desirable behavior ihmo - is now broken. So there's a bug (maybe recent?) indeed, will investigate.

[ocornut]

Amusingly this case got broken by:
Fix IsWindowAppearing() from returning true twice in most cases. (#3982, #1497, #1061)
84e6fe4

[ocornut]

Pushed a fix here: 91704b7
Thank you!

[ocornut]

This is a more complex than expected, because they are cases were IsWindowAppearing() would return true while Begin() returned false, meaning users may not submit contents. We are working on it.

[ocornut]

Pushed two extra commits which should fix the issues we encountered.

Also added a sanity assert to ensure that Begin() never returns false when the Appearing flag is set.