Imgui: Restrict window movement / position

[enelija]

Version/Branch of Dear ImGui:

Version: dear imgui, v1.73
Branch: master

Screenshots/Video

My Issue/Question:
Hello!

Is there any possibility to restrict / constraint the movement of windows to a specific area, in my case to a fixed minimum y position? (like a SetNextWindowPosConstraints or similar)
I have a menu and an icon bar at the top and would like to prevent users to move any other Dear ImGui window over these two bars (prevent overlapping).

What I have tried (not working):

ImGui::Begin("Settings");

ImGuiContext& g = *GImGui;
if (g.MovingWindow != NULL && g.IO.MousePos.y < (topY + g.ActiveIdClickOffset.y))
{
    g.IO.MousePos.y = topY + g.ActiveIdClickOffset.y;
    // also tried to set the g.IO.MousePos.y invalid here 
}
ImGui::End();

Thanks!

[ocornut]

While I'm not against a potential SetNextWindowPosConstraints() api call, I think the problem you are trying to solve is common and rather specific and I believe we should come up with a more dedicated solution.

In OS terminology there is usually a "Work Area" per monitor, which is the monitor rectangle minor task-bar etc. and we could envision having a similar system per viewport. So instead of using a positioning constraint, the menus/bars windows would register themselves are eating space off the work area.

[enelija]

Windows consuming space from the work area sounds even better.
Are you aware of any work-around for now?

[ocornut]

I don't think there is, no.

[enelija]

My current work-around (consuming the resize grip area without displaying content there):

void Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
{
    ImGui::Begin(name, p_open, ImGuiWindowFlags_NoScrollbar | ImGuiWindowFlags_NoScrollWithMouse);

    const auto height{ ImGui::GetWindowContentRegionMax().y - ImGui::GetWindowContentRegionMin().y };
    ImGui::BeginChild("1_Content", ImVec2(0, height - Style::resizeGripHeight), false, flags);
}

void End()
{
    ImGui::EndChild();
    ImGui::BeginChild("2_ResizeGrip", ImVec2(0.0f, Style::resizeGripHeight), false, ImGuiWindowFlags_NoScrollbar | ImGuiWindowFlags_NoScrollWithMouse);
    ImGui::EndChild();
    ImGui::End();
}

[ocornut]

Note that 75de34e281141f851f7e5f9f6a923573167bc0f0 added a per-viewport work-area in the docking branch, and position clamping uses this work area. So in docking branch if you have a main-menu bar you can position a window entirely behind it.