Method ScrollbarEx

tutorials/common/imgui/imgui_widgets.cpp:924–1014

Vertical/Horizontal scrollbar The entire piece of code below is rather confusing because: - We handle absolute seeking (when first clicking outside the grab) and relative manipulation (afterward or when clicking inside the grab) - We store values as normalized ratio and in a form that allows the window content to change while we are holding on a scrollbar - We handle both horizontal and vertical s

// - We handle both horizontal and vertical scrollbars, which makes the terminology not ideal.
// Still, the code should probably be made simpler..
bool ImGui::ScrollbarEx(const ImRect& bb_frame, ImGuiID id, ImGuiAxis axis, ImS64* p_scroll_v, ImS64 size_avail_v, ImS64 size_contents_v, ImDrawFlags flags)
{
    ImGuiContext& g = *GImGui;
    ImGuiWindow* window = g.CurrentWindow;
    if (window->SkipItems)
        return false;

    const float bb_frame_width = bb_frame.GetWidth();
    const float bb_frame_height = bb_frame.GetHeight();
    if (bb_frame_width <= 0.0f || bb_frame_height <= 0.0f)
        return false;

    // When we are too small, start hiding and disabling the grab (this reduce visual noise on very small window and facilitate using the window resize grab)
    float alpha = 1.0f;
    if ((axis == ImGuiAxis_Y) && bb_frame_height < g.FontSize + g.Style.FramePadding.y * 2.0f)
        alpha = ImSaturate((bb_frame_height - g.FontSize) / (g.Style.FramePadding.y * 2.0f));
    if (alpha <= 0.0f)
        return false;

    const ImGuiStyle& style = g.Style;
    const bool allow_interaction = (alpha >= 1.0f);

    ImRect bb = bb_frame;
    bb.Expand(ImVec2(-ImClamp(IM_FLOOR((bb_frame_width - 2.0f) * 0.5f), 0.0f, 3.0f), -ImClamp(IM_FLOOR((bb_frame_height - 2.0f) * 0.5f), 0.0f, 3.0f)));

    // V denote the main, longer axis of the scrollbar (= height for a vertical scrollbar)
    const float scrollbar_size_v = (axis == ImGuiAxis_X) ? bb.GetWidth() : bb.GetHeight();

    // Calculate the height of our grabbable box. It generally represent the amount visible (vs the total scrollable amount)
    // But we maintain a minimum size in pixel to allow for the user to still aim inside.
    IM_ASSERT(ImMax(size_contents_v, size_avail_v) > 0.0f); // Adding this assert to check if the ImMax(XXX,1.0f) is still needed. PLEASE CONTACT ME if this triggers.
    const ImS64 win_size_v = ImMax(ImMax(size_contents_v, size_avail_v), (ImS64)1);
    const float grab_h_pixels = ImClamp(scrollbar_size_v * ((float)size_avail_v / (float)win_size_v), style.GrabMinSize, scrollbar_size_v);
    const float grab_h_norm = grab_h_pixels / scrollbar_size_v;

    // Handle input right away. None of the code of Begin() is relying on scrolling position before calling Scrollbar().
    bool held = false;
    bool hovered = false;
    ItemAdd(bb_frame, id, NULL, ImGuiItemFlags_NoNav);
    ButtonBehavior(bb, id, &hovered, &held, ImGuiButtonFlags_NoNavFocus);

    const ImS64 scroll_max = ImMax((ImS64)1, size_contents_v - size_avail_v);
    float scroll_ratio = ImSaturate((float)*p_scroll_v / (float)scroll_max);
    float grab_v_norm = scroll_ratio * (scrollbar_size_v - grab_h_pixels) / scrollbar_size_v; // Grab position in normalized space
    if (held && allow_interaction && grab_h_norm < 1.0f)
    {
        const float scrollbar_pos_v = bb.Min[axis];
        const float mouse_pos_v = g.IO.MousePos[axis];

        // Click position in scrollbar normalized space (0.0f->1.0f)
        const float clicked_v_norm = ImSaturate((mouse_pos_v - scrollbar_pos_v) / scrollbar_size_v);
        SetHoveredID(id);

        bool seek_absolute = false;
        if (g.ActiveIdIsJustActivated)
        {
            // On initial click calculate the distance between mouse and the center of the grab
            seek_absolute = (clicked_v_norm < grab_v_norm || clicked_v_norm > grab_v_norm + grab_h_norm);