Add custom button in window title bar

[s-pravin]

Version/Branch of Dear ImGui:

Version: 1.81
Branch: docking

Back-end/Renderer/Compiler/OS

Back-ends: imgui_impl_glfw.cpp + imgui_impl_opengl3.cpp
Operating System: Windows 10

My Issue/Question:

I am trying to customize ImGui window title bar by adding a custom button over it. Though, button content gets rendered as per expectation, button click isn't captured. I have set cursor position to the button location before invoking ItemSize, but am not confident if that's the correct way to achieve this.

• Does anyone know why button click isn't captured in the example below?
• Any downsides to adding custom button in title bar? I am trying to achieve functionality offered by Pin button in Visual Studio e.g. Solution Explorer/Properties etc.

Standalone, minimal, complete and verifiable example:

        ImGui::SetNextWindowSize(ImVec2(200, 200));
        ImGui::Begin("Demo Window");
        ImGuiWindow* curWindow = ImGui::GetCurrentWindow();
        ImDrawList* drawList = ImGui::GetForegroundDrawList(curWindow);
        ImRect titlePos = curWindow->TitleBarRect();

        ImGuiContext& g = *GImGui;
        const ImGuiID id = curWindow->GetID("#snap");

        const ImRect bb(ImVec2(titlePos.Max.x - 30, titlePos.Max.y - 15), ImVec2(titlePos.Max.x - 10, titlePos.Max.y - 7));
        ImGui::SetCursorScreenPos(bb.Min);
        ImGui::SetCursorPos(bb.Min);
        ImGui::ItemSize(bb);
        ImGui::ItemAdd(bb, id);

        bool hovered, held;
        bool pressed = ImGui::ButtonBehavior(bb, id, &hovered, &held);

        // Render
        const ImU32 col = ImGui::GetColorU32((held && hovered) ? ImGuiCol_ButtonActive : hovered ? ImGuiCol_ButtonHovered : ImGuiCol_Button);
        ImGui::RenderNavHighlight(bb, id);
        ImGui::RenderFrame(bb.Min, bb.Max, col, true);
        drawList->AddRectFilled(bb.Min, bb.Max, ImGui::GetColorU32(ImVec4(1.0f, 1.0f, 1.0f, 1.0f)));
        drawList->AddTriangleFilled(ImVec2(titlePos.Max.x - 30, titlePos.Max.y - 7), ImVec2(titlePos.Max.x - 10, titlePos.Max.y - 7), ImVec2(titlePos.Max.x - 20, titlePos.Max.y - 15), ImGui::GetColorU32(ImVec4(1.0f, 0.0f, 0.0f, 1.0f)));

        ImGui::SetCursorScreenPos(curWindow->ContentRegionRect.Min);
        ImGui::Text("Test Content");
        if (pressed)
            ImGui::Text("Button pressed");
        ImGui::End();

[ocornut]

There are two things at play here:

• After Begin() the window has a clip rectangle to cover only the scrollable client area, and interactions are affected by this clipping rectangle. You may need to manually call PushClipRect()/PopClipRect() to temporarily access to the whole area outside the window client area.

• May or not affect you: by default Hovering tests are performed on a "first come first served" (~back to front) basis, so when two items are overlapping the first one will get the Hover and generally be able to interact. Using SetItemAllowOverlap() we have a (currently ill-defined and bit messy) mechanism to allow "last come first served" (~front to back) hovering tests. There are various treacherous aspect to the current implementation which I won't get into detail right now, but SetItemAllowOverlap() is not always sufficient currently.
  The reason I say this may not affect you is that the Title Bar actually doesn't submit a regular item, and therefore I think may not be affected by this requirement anyway.