Method update_scroll_containers

src/engine.rs:5398–5682

(
        &mut self,
        enable_drag_scrolling: bool,
        scroll_delta: Vector2,
        delta_time: f32,
        touch_input_active: bool,
    )

    const SCROLL_VELOCITY_SMOOTHING: f32 = 0.4; // EMA factor for velocity tracking

    pub fn update_scroll_containers(
        &mut self,
        enable_drag_scrolling: bool,
        scroll_delta: Vector2,
        delta_time: f32,
        touch_input_active: bool,
    ) {
        let pointer = self.pointer_info.position;
        let dt = delta_time.max(0.0001); // Guard against zero/negative dt

        // Remove containers that weren't open this frame, reset flag for next frame
        let mut i = 0;
        while i < self.scroll_container_datas.len() {
            if !self.scroll_container_datas[i].open_this_frame {
                self.scroll_container_datas.swap_remove(i);
                continue;
            }
            self.scroll_container_datas[i].open_this_frame = false;
            i += 1;
        }

        for scd in &mut self.scroll_container_datas {
            scd.scrollbar_activity_this_frame = false;
        }

        // --- Drag scrolling ---
        if enable_drag_scrolling {
            let pointer_state = self.pointer_info.state;

            match pointer_state {
                PointerDataInteractionState::PressedThisFrame => {
                    // Find the deepest scroll container under the pointer and start drag
                    let mut best: Option<usize> = None;
                    for si in 0..self.scroll_container_datas.len() {
                        let scd = &self.scroll_container_datas[si];
                        let bb = scd.bounding_box;
                        if pointer.x >= bb.x
                            && pointer.x <= bb.x + bb.width
                            && pointer.y >= bb.y
                            && pointer.y <= bb.y + bb.height
                        {
                            best = Some(si);
                        }
                    }
                    if let Some(si) = best {
                        let scd = &mut self.scroll_container_datas[si];
                        scd.scroll_momentum = Vector2::default();
                        scd.previous_delta = Vector2::default();

                        scd.pointer_scroll_active = false;
                        scd.scrollbar_thumb_drag_active_x = false;
                        scd.scrollbar_thumb_drag_active_y = false;

                        let mut started_thumb_drag = false;
                        if let Some(scrollbar_cfg) = scd.scrollbar {
                            let alpha = scrollbar_visibility_alpha(scrollbar_cfg, scd.scrollbar_idle_frames);
                            if alpha > 0.0 {
                                if scd.scroll_y_enabled {