Draggable

A container widget that can be dragged with pointer input. The drag offset is applied as a paint-time translate, so the Taitank layout is unaffected.

Overview

Draggable extends Container and overrides pointer event handlers to track drag state. When the user presses and moves the pointer, the widget's visual position is offset by the drag delta. The layout position (as computed by Taitank) remains unchanged.

State Machine

Draggable uses a lightweight state machine with three states:

State	Description
kIdle	Pointer is not interacting with the widget.
kHovering	Pointer is over the widget but not pressed.
kDragging	Pointer is pressed and moving the widget.

State transitions are triggered by pointer events:

• OnPointerEnter → kHovering (if not dragging)
• OnPointerExit → kIdle (if not dragging)
• OnPointerDown → kDragging
• OnPointerUp → kIdle

Usage

#include <neoflux/widget/draggable.h>

auto box = std::make_shared<Draggable>();
box->SetWidth(100.0F)
   .SetHeight(100.0F)
   .SetBackgroundColor({.r = 51, .g = 128, .b = 230, .a = 255})
   .SetBorderRadius(12.0F);

auto label = std::make_shared<Text>("Drag Me");
box->AddChild(label);

API Reference

Methods

Method	Description
GetDragOffset() -> Point	Returns the current drag offset (x, y).
IsDragging() -> bool	Returns true if the widget is currently being dragged.

Overridden Events

Event	Behavior
OnPointerDown(pos)	Records press position, sets dragging state.
OnPointerUp(pos)	Ends drag, returns to idle state.
OnPointerMove(pos)	Updates drag offset when dragging, marks needs build.
OnPointerEnter()	Transitions to hovering state.
OnPointerExit()	Transitions to idle state.
Paint(ctx)	Saves context, translates by drag offset, paints children, restores.

Long-Press Detection Pattern

Combine Draggable with coroutines for long-press detection. The state machine acts as a "condition lock": a coroutine launched on pointer-down checks the widget state after sleeping; if the state has changed (pointer released), the coroutine returns silently.

class DragBox : public Draggable {
 public:
  bool OnPointerDown(const Point& local_pos) override {
    Draggable::OnPointerDown(local_pos);
    auto weak = std::weak_ptr<DragBox>(
        std::static_pointer_cast<DragBox>(shared_from_this()));
    app_->GetEventLoop().Schedule(LongPressCoroutine(weak));
    return true;
  }

 private:
  static Task<void> LongPressCoroutine(std::weak_ptr<DragBox> weak) {
    co_await Sleep(std::chrono::milliseconds(500));
    auto box = weak.lock();
    if (!box || !box->IsDragging()) co_return;
    // Long press detected.
  }
};

See Also

• Widget
• Container
• ScrollView