Method UpdateWindowManualResize

src/imgui/imgui.cpp:6730–6943

Handle resize for: Resize Grips, Borders, Gamepad Return true when using auto-fit (double-click on resize grip)

// Handle resize for: Resize Grips, Borders, Gamepad
// Return true when using auto-fit (double-click on resize grip)
static int ImGui::UpdateWindowManualResize(ImGuiWindow* window, const ImVec2& size_auto_fit, int* border_hovered, int* border_held, int resize_grip_count, ImU32 resize_grip_col[4], const ImRect& visibility_rect)
{
    ImGuiContext& g = *GImGui;
    ImGuiWindowFlags flags = window->Flags;

    if ((flags & ImGuiWindowFlags_NoResize) || window->AutoFitFramesX > 0 || window->AutoFitFramesY > 0)
        return false;
    if ((flags & ImGuiWindowFlags_AlwaysAutoResize) && (window->ChildFlags & (ImGuiChildFlags_ResizeX | ImGuiChildFlags_ResizeY)) == 0)
        return false;
    if (window->WasActive == false) // Early out to avoid running this code for e.g. a hidden implicit/fallback Debug window.
        return false;

    int ret_auto_fit_mask = 0x00;
    const float grip_draw_size = IM_TRUNC(ImMax(g.FontSize * 1.35f, window->WindowRounding + 1.0f + g.FontSize * 0.2f));
    const float grip_hover_inner_size = (resize_grip_count > 0) ? IM_TRUNC(grip_draw_size * 0.75f) : 0.0f;
    const float grip_hover_outer_size = g.WindowsBorderHoverPadding;

    ImRect clamp_rect = visibility_rect;
    const bool window_move_from_title_bar = g.IO.ConfigWindowsMoveFromTitleBarOnly && !(window->Flags & ImGuiWindowFlags_NoTitleBar);
    if (window_move_from_title_bar)
        clamp_rect.Min.y -= window->TitleBarHeight;

    ImVec2 pos_target(FLT_MAX, FLT_MAX);
    ImVec2 size_target(FLT_MAX, FLT_MAX);

    // Resize grips and borders are on layer 1
    window->DC.NavLayerCurrent = ImGuiNavLayer_Menu;

    // Manual resize grips
    PushID("#RESIZE");
    for (int resize_grip_n = 0; resize_grip_n < resize_grip_count; resize_grip_n++)
    {
        const ImGuiResizeGripDef& def = resize_grip_def[resize_grip_n];
        const ImVec2 corner = ImLerp(window->Pos, window->Pos + window->Size, def.CornerPosN);

        // Using the FlattenChilds button flag we make the resize button accessible even if we are hovering over a child window
        bool hovered, held;
        ImRect resize_rect(corner - def.InnerDir * grip_hover_outer_size, corner + def.InnerDir * grip_hover_inner_size);
        if (resize_rect.Min.x > resize_rect.Max.x) ImSwap(resize_rect.Min.x, resize_rect.Max.x);
        if (resize_rect.Min.y > resize_rect.Max.y) ImSwap(resize_rect.Min.y, resize_rect.Max.y);
        ImGuiID resize_grip_id = window->GetID(resize_grip_n); // == GetWindowResizeCornerID()
        ItemAdd(resize_rect, resize_grip_id, NULL, ImGuiItemFlags_NoNav);
        ButtonBehavior(resize_rect, resize_grip_id, &hovered, &held, ImGuiButtonFlags_FlattenChildren | ImGuiButtonFlags_NoNavFocus);
        //GetForegroundDrawList(window)->AddRect(resize_rect.Min, resize_rect.Max, IM_COL32(255, 255, 0, 255));
        if (hovered || held)
            SetMouseCursor((resize_grip_n & 1) ? ImGuiMouseCursor_ResizeNESW : ImGuiMouseCursor_ResizeNWSE);

        if (held && g.IO.MouseDoubleClicked[0])
        {
            // Auto-fit when double-clicking
            size_target = CalcWindowSizeAfterConstraint(window, size_auto_fit);
            ret_auto_fit_mask = 0x03; // Both axes
            ClearActiveID();
        }
        else if (held)
        {
            // Resize from any of the four corners
            // We don't use an incremental MouseDelta but rather compute an absolute target size based on mouse position