Bug with Experimental Feature: BeginComboPreview

[BobbyAnguelov]

(you may also go to Demo>About Window, and click "Config/Build Information" to obtain a bunch of detailed information that you can paste here)

Version/Branch of Dear ImGui:

Dear ImGui 1.89.6 (18960)
--------------------------------
sizeof(size_t): 8, sizeof(ImDrawIdx): 2, sizeof(ImDrawVert): 20
define: __cplusplus=199711
define: _WIN32
define: _WIN64
define: _MSC_VER=1936
define: _MSVC_LANG=201402
define: IMGUI_HAS_VIEWPORT
define: IMGUI_HAS_DOCK
--------------------------------
io.BackendPlatformName: imgui_impl_win32
io.BackendRendererName: imgui_impl_dx11
io.ConfigFlags: 0x00000443
 NavEnableKeyboard
 NavEnableGamepad
 DockingEnable
 ViewportsEnable
io.ConfigViewportsNoDecoration
io.ConfigInputTextCursorBlink
io.ConfigWindowsResizeFromEdges
io.ConfigMemoryCompactTimer = 60.0
io.BackendFlags: 0x00001C0E
 HasMouseCursors
 HasSetMousePos
 PlatformHasViewports
 HasMouseHoveredViewport
 RendererHasVtxOffset
 RendererHasViewports
--------------------------------
io.Fonts: 1 fonts, Flags: 0x00000000, TexSize: 512,64
io.DisplaySize: 1264.00,761.00
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

Operating System: Windows11

My Issue/Question:

So this is super weird, but using the code below:

ImGui::Begin( "Repro" );
if ( ImGui::BeginChild( "DAS", ImVec2( -1, ImGui::GetFrameHeightWithSpacing() ) ) )
{
    ImGui::SetNextItemWidth( -1 );
    if ( ImGui::BeginCombo( "##Test", "", ImGuiComboFlags_CustomPreview ) )
    {
        ImGui::EndCombo();
    }

    if ( ImGui::BeginComboPreview() )
    {
        ImGui::Text( "Preview" );
        ImGui::EndComboPreview();
    }
}
ImGui::EndChild();
ImGui::End();

This works when the imgui window is on my main monitor but if I move it to a secondary monitor (to the left so negative x coords), then preview stops displaying due to the narrow test on line 1838 in imgui_widgets.cpp failing. Shouldn't that line read:

if (!window->ClipRect.Overlaps(preview_data->PreviewRect))

instead of

if (!window->ClipRect.Contains(preview_data->PreviewRect))

Changing that fixes the issue. Also this only seems to occur when you put the combo inside of a child window.

[ocornut]

You are correct. I have pushed your fix as a134892
(It's not merged in docking until a few days but I have confirmed it cherry-pick fines on docking, if you need a merge sooner let me know) merfged in docking since I had another fix pushed for something else.

Thank you for reporting and fixing!

PS: To clarify, it's not due to negative coordinates per se, but happened if the preview rectangle was not entirely contained within the parent window current clipping rectangle.