SelectableFlags_SpanAllColumns doesn't span all columns when horizontal scrolling

[PazerOP]

Dear ImGui version/build info:

Dear ImGui 1.77 WIP (17601)
--------------------------------
sizeof(size_t): 8, sizeof(ImDrawIdx): 2, sizeof(ImDrawVert): 20
define: __cplusplus=201705
define: _WIN32
define: _WIN64
define: _MSC_VER=1925
--------------------------------
io.BackendPlatformName: imgui_impl_sdl
io.BackendRendererName: imgui_impl_opengl3
io.ConfigFlags: 0x00000001
 NavEnableKeyboard
io.ConfigInputTextCursorBlink
io.ConfigWindowsResizeFromEdges
io.ConfigWindowsMemoryCompactTimer = 60.0f
io.BackendFlags: 0x00000006
 HasMouseCursors
 HasSetMousePos
--------------------------------
io.Fonts: 1 fonts, Flags: 0x00000000, TexSize: 512,64
io.DisplaySize: 800.00,600.00
io.DisplayFramebufferScale: 1.00,1.00
--------------------------------
style.WindowPadding: 8.00,8.00
style.WindowBorderSize: 0.00
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

Version/Branch of Dear ImGui:

Lastest commit on master at the current time, a2454f2

Back-end/Renderer/Compiler/OS

Back-ends: imgui_impl_sdl.cpp + imgui_impl_opengl3.cpp
Compiler: VS2019 16.5.0
Operating System: Windows 10 1909 (18363)

My Issue/Question:

When the current window is scrolled horizontally, ImGuiSelectableFlags_SpanAllColumns doesn't work properly. It appears to stop where the visible area would end if the window was not being scrolled horizontally. This is not just a cosmetic issue, it affects hit testing as well (moving the mouse to the right of the blue area in the selectable causes it to leave the hovered state).

I considered submitting a pull request that changed window->ContentRegionRect to window->DC.CurrentColumns->HostWorkRect on both lines of

imgui/imgui_widgets.cpp

Lines 5617 to 5618 in a2454f2

	const float min_x = (flags & ImGuiSelectableFlags_SpanAllColumns) ? window->ContentRegionRect.Min.x : pos.x;
	const float max_x = (flags & ImGuiSelectableFlags_SpanAllColumns) ? window->ContentRegionRect.Max.x : GetContentRegionMaxAbs().x;

, which appears to fix the issue, but I have no idea if that is the "correct" way of fixing the issue.

Screenshots/Video

The minimal example code below produces the following window:

However, if we scroll to the right, we see the selectable in the first column is actually clamped to the initially visible region of the window:

Standalone, minimal, complete and verifiable example:

ImGui::SetNextWindowSize({ 300, 300 }, ImGuiCond_Always);
if (ImGui::Begin("TestWindow", nullptr, ImGuiWindowFlags_HorizontalScrollbar))
{
	ImGui::Columns(2);

	ImGui::Selectable("A Selectable In A Column", true, ImGuiSelectableFlags_SpanAllColumns); ImGui::NextColumn();
	ImGui::Text("Very long column 2 aaaaaaaaaaaaaaaaaaaaaaaa"); ImGui::NextColumn();
	ImGui::Columns();

	ImGui::Text("A very long string of text that forces the content width to be wide enough that horizontal scrollbars show up");
}
ImGui::End();

[zodiacon]

It doesn't seem to solve the issue completely with Tables. When scrolling horizontally (with SpanAllColumns), it does highlight the entire row BUT clicking at the area scrolled in is ignored.
(Probably a related bug)

[ocornut]

Thanks @PazerOP for reporting this.
This should now be fixed in master (by 8074b49).

Various tests for it:

if (ImGui::Begin("Test A", NULL, ImGuiWindowFlags_HorizontalScrollbar))
{
    ImGui::Button("Spacer", ImVec2(500, 0));
    ImGui::Selectable("Selectable");
    if (ImGui::TreeNodeEx("TreeNode", ImGuiTreeNodeFlags_SpanAvailWidth))
        ImGui::TreePop();
}
ImGui::End();

ImGui::SetNextWindowSize(ImVec2(300, 300), ImGuiCond_Once);
if (ImGui::Begin("Test B #3187", NULL, ImGuiWindowFlags_HorizontalScrollbar))
{
    ImGui::Columns(2);

    ImGui::Selectable("Selectable Col 0 Regular", false);
    ImGui::Selectable("Selectable Col 0 SpanAllColumns", false, ImGuiSelectableFlags_SpanAllColumns);
    ImGui::NextColumn();
    ImGui::Text("Very long column 2 aaaaaaaaaaaaaaaaaaaaaaaa");
    ImGui::NextColumn();

    ImGui::Text("Blah blah");
    ImGui::NextColumn();
    ImGui::Selectable("Selectable Col 1 Regular", false);
    ImGui::Selectable("Selectable Col 1 SpanAllColumns", false, ImGuiSelectableFlags_SpanAllColumns);
    ImGui::NextColumn();

    ImGui::Columns();

    ImGui::Text("A very long string of text that forces the content width to be wide enough that horizontal scrollbars show up");
}
ImGui::End();

#ifdef IMGUI_HAS_TABLE
if (ImGui::Begin("Test C #3386"))
{
    if (ImGui::BeginTable("Table", 2, ImGuiTableFlags_ScrollFreezeTopRow | ImGuiTableFlags_Scroll | ImGuiTableFlags_ScrollFreezeLeftColumn))
    {
        ImGui::TableSetupColumn("Col 1", ImGuiTableColumnFlags_WidthFixed | ImGuiTableColumnFlags_NoHide, 200);
        ImGui::TableSetupColumn("Col 2", ImGuiTableColumnFlags_WidthFixed, 200);
        ImGui::TableAutoHeaders();

        ImGui::TableNextRow();
        ImGui::TableSetColumnIndex(0);

        ImGui::Selectable("Selectable Col 0 Regular");
        ImGui::Selectable("Selectable Col 0 SpanAllColumns", false, ImGuiSelectableFlags_SpanAllColumns);
        if (ImGui::TableNextCell())
            ImGui::TextUnformatted("Blah blah");

        ImGui::TableNextRow();
        ImGui::TableSetColumnIndex(0);
        ImGui::TextUnformatted("Blah blah");

        ImGui::TableSetColumnIndex(1);
        ImGui::Selectable("Selectable Col 1 Regular");
        ImGui::Selectable("Selectable Col 1 SpanAllColumns", false, ImGuiSelectableFlags_SpanAllColumns);

        ImGui::EndTable();
    }
}
ImGui::End();
#endif