ConfigWindowsMoveFromTitleBarOnly flag prevents dragging windows across vertically arranged displays.

[lailoken]

Version/Branch of Dear ImGui:

Version 1.90

Back-ends:

imgui_impl_dx11.cpp

Compiler, OS:

Windows 11 + MSVC 2017

Full config/build information:

Dear ImGui 1.90.0 (19000)
--------------------------------
sizeof(size_t): 8, sizeof(ImDrawIdx): 4, sizeof(ImDrawVert): 20
define: __cplusplus=199711
define: IMGUI_DISABLE_OBSOLETE_FUNCTIONS
define: IMGUI_DISABLE_OBSOLETE_KEYIO
define: _WIN32
define: _WIN64
define: _MSC_VER=1938
define: _MSVC_LANG=201402
define: IMGUI_HAS_VIEWPORT
define: IMGUI_HAS_DOCK
--------------------------------
io.BackendPlatformName: imgui_impl_win32
io.BackendRendererName: imgui_impl_dx11
io.ConfigFlags: 0x00004441
 NavEnableKeyboard
 DockingEnable
 ViewportsEnable
 DpiEnableScaleViewports
io.ConfigViewportsNoDecoration
io.ConfigDockingWithShift
io.ConfigInputTextCursorBlink
io.ConfigWindowsResizeFromEdges
io.ConfigMemoryCompactTimer = 60.0
io.BackendFlags: 0x00001C0E
 HasMouseCursors
 HasSetMousePos
 PlatformHasViewports
 HasMouseHoveredViewport
 RendererHasVtxOffset
 RendererHasViewports
--------------------------------
io.Fonts: 9 fonts, Flags: 0x00000000, TexSize: 2048,2048
io.DisplaySize: 1912.00,1332.00
io.DisplayFramebufferScale: 1.00,1.00
--------------------------------
style.WindowPadding: 3.00,3.00
style.WindowBorderSize: 1.00
style.FramePadding: 4.00,2.00
style.FrameRounding: 0.00
style.FrameBorderSize: 1.00
style.ItemSpacing: 6.00,3.00
style.ItemInnerSpacing: 3.00,3.00

Details:

When I have a displays arranged vertically (one above another), I am unable to drag windows from a lower display to a higher display.

I have found that this is due to the following line:

io.ConfigWindowsMoveFromTitleBarOnly = true;

And when I set that to false it works again.
(Also, when it is true, dragging a window down into a lower display works well until the window is about halfway into the lower display, when it suddenly jumps the entire window onto the lower display)

I also notice that toggling: ConfigViewportsNoDecoration to false (showing windows default decoration) fixes it.

Screenshots/Video:

Minimal, Complete and Verifiable Example code:

No response

[ocornut]

Just in case, can you report the coordinates of all monitors as reported in Metrics->Viewport?

[lailoken]

I've tried with monitor both below and above my main (3) display, same problem:

[ocornut]

I currently don't have multiple monitors to test with, but I guess this is causing the issue:

            else if (window->ViewportOwned && g.PlatformIO.Monitors.Size > 0)
            {
                // Lost windows (e.g. a monitor disconnected) will naturally moved to the fallback/dummy monitor aka the main viewport.
                const ImGuiPlatformMonitor* monitor = GetViewportPlatformMonitor(window->Viewport);
                visibility_rect.Min = monitor->WorkPos + visibility_padding;
                visibility_rect.Max = monitor->WorkPos + monitor->WorkSize - visibility_padding;
                ClampWindowPos(window, visibility_rect);
            }

static inline void ClampWindowPos(ImGuiWindow* window, const ImRect& visibility_rect)
{
    ImGuiContext& g = *GImGui;
    ImVec2 size_for_clamping = window->Size;
    if (g.IO.ConfigWindowsMoveFromTitleBarOnly && (!(window->Flags & ImGuiWindowFlags_NoTitleBar) || window->DockNodeAsHost))
        size_for_clamping.y = ImGui::GetFrameHeight(); // Not using window->TitleBarHeight() as DockNodeAsHost will report 0.0f here.
    window->Pos = ImClamp(window->Pos, visibility_rect.Min - size_for_clamping, visibility_rect.Max);
}

Our way of clamping position use monitor boundaries. Problem is that we can have rectangular boundaries encompassing all monitors area, so we may need to do thing differently while moving a window vs when not moving it.
While moving we could use the bounding box of all monitors.

[ocornut]

Actually same as #3071

[lailoken]

I'll follow the other ticket. (missed it)

[ocornut]

Should be fixed with 30ba3c3 !