Function ShowExampleAppConstrainedResize

core/src/imgui/imgui_demo.cpp:7032–7078

Demonstrate creating a window with custom resize constraints.

// Demonstrate creating a window with custom resize constraints.
static void ShowExampleAppConstrainedResize(bool* p_open)
{
    struct CustomConstraints
    {
        // Helper functions to demonstrate programmatic constraints
        static void Square(ImGuiSizeCallbackData* data) { data->DesiredSize.x = data->DesiredSize.y = IM_MAX(data->DesiredSize.x, data->DesiredSize.y); }
        static void Step(ImGuiSizeCallbackData* data)   { float step = (float)(int)(intptr_t)data->UserData; data->DesiredSize = ImVec2((int)(data->DesiredSize.x / step + 0.5f) * step, (int)(data->DesiredSize.y / step + 0.5f) * step); }
    };

    const char* test_desc[] =
    {
        "Resize vertical only",
        "Resize horizontal only",
        "Width > 100, Height > 100",
        "Width 400-500",
        "Height 400-500",
        "Custom: Always Square",
        "Custom: Fixed Steps (100)",
    };

    static bool auto_resize = false;
    static int type = 0;
    static int display_lines = 10;
    if (type == 0) ImGui::SetNextWindowSizeConstraints(ImVec2(-1, 0),    ImVec2(-1, FLT_MAX));      // Vertical only
    if (type == 1) ImGui::SetNextWindowSizeConstraints(ImVec2(0, -1),    ImVec2(FLT_MAX, -1));      // Horizontal only
    if (type == 2) ImGui::SetNextWindowSizeConstraints(ImVec2(100, 100), ImVec2(FLT_MAX, FLT_MAX)); // Width > 100, Height > 100
    if (type == 3) ImGui::SetNextWindowSizeConstraints(ImVec2(400, -1),  ImVec2(500, -1));          // Width 400-500
    if (type == 4) ImGui::SetNextWindowSizeConstraints(ImVec2(-1, 400),  ImVec2(-1, 500));          // Height 400-500
    if (type == 5) ImGui::SetNextWindowSizeConstraints(ImVec2(0, 0),     ImVec2(FLT_MAX, FLT_MAX), CustomConstraints::Square);                     // Always Square
    if (type == 6) ImGui::SetNextWindowSizeConstraints(ImVec2(0, 0),     ImVec2(FLT_MAX, FLT_MAX), CustomConstraints::Step, (void*)(intptr_t)100); // Fixed Step

    ImGuiWindowFlags flags = auto_resize ? ImGuiWindowFlags_AlwaysAutoResize : 0;
    if (ImGui::Begin("Example: Constrained Resize", p_open, flags))
    {
        if (ImGui::Button("200x200")) { ImGui::SetWindowSize(ImVec2(200, 200)); } ImGui::SameLine();
        if (ImGui::Button("500x500")) { ImGui::SetWindowSize(ImVec2(500, 500)); } ImGui::SameLine();
        if (ImGui::Button("800x200")) { ImGui::SetWindowSize(ImVec2(800, 200)); }
        ImGui::SetNextItemWidth(200);
        ImGui::Combo("Constraint", &type, test_desc, IM_ARRAYSIZE(test_desc));
        ImGui::SetNextItemWidth(200);
        ImGui::DragInt("Lines", &display_lines, 0.2f, 1, 100);
        ImGui::Checkbox("Auto-resize", &auto_resize);
        for (int i = 0; i < display_lines; i++)
            ImGui::Text("%*sHello, sailor! Making this line long enough for the example.", i * 4, "");
    }
    ImGui::End();
}

//-----------------------------------------------------------------------------
// [SECTION] Example App: Simple overlay / ShowExampleAppSimpleOverlay()