RmlUi/Source/Core/ScrollController.h

#pragma once

#include "../../Include/RmlUi/Core/Header.h"
#include "../../Include/RmlUi/Core/ScrollTypes.h"
#include "../../Include/RmlUi/Core/Types.h"

namespace Rml {

/**
    Implements scrolling behavior that occurs over time.

    Scrolling modes are activated externally, targeting a given element. The actual scrolling takes place during update calls.
 */

class ScrollController {
public:
	enum class Mode {
		None,
		Smoothscroll, // Smooth scrolling to target distance.
		Autoscroll,   // Scrolling with middle mouse button.
		Inertia,      // Applying scrolling inertia when using swipe gesture
	};

	void ActivateAutoscroll(Element* target, Vector2i start_position);
	void ActivateSmoothscroll(Element* target, Vector2f delta_distance, ScrollBehavior scroll_behavior);
	void ActivateInertia(Element* target, Vector2f velocity);

	void InstantScrollOnTarget(Element* target, Vector2f delta_distance);

	bool Update(Vector2i mouse_position, float dp_ratio);

	void IncrementSmoothscrollTarget(Vector2f delta_distance);

	// Resets any active mode and its state.
	void Reset();

	// Sets the scroll behavior for mouse wheel processing and scrollbar interaction.
	void SetDefaultScrollBehavior(ScrollBehavior scroll_behavior, float speed_factor);

	// Returns the autoscroll cursor based on the active scroll velocity.
	String GetAutoscrollCursor(Vector2i mouse_position, float dp_ratio) const;
	// Returns true if autoscroll mode is active and the cursor has been moved outside the idle scroll area.
	bool HasAutoscrollMoved() const;

	Mode GetMode() const { return mode; }
	Element* GetTarget() const { return target; }

private:
	// Updates time to now, and returns the delta time since the previous time update.
	float UpdateTime();

	void UpdateAutoscroll(float dt, Vector2i mouse_position, float dp_ratio);

	void UpdateSmoothscroll(float dt, float dp_ratio);

	void UpdateInertia(float dt);

	bool HasSmoothscrollReachedTarget() const;

	void PerformScrollOnTarget(Vector2f delta_distance);

	Mode mode = Mode::None;

	Element* target = nullptr;
	double previous_update_time = 0;

	Vector2i autoscroll_start_position;
	Vector2f autoscroll_accumulated_length;
	bool autoscroll_moved = false;

	bool smoothscroll_prefer_instant = false;
	float smoothscroll_speed_factor = 1.f;

	Vector2f smoothscroll_target_distance;
	Vector2f smoothscroll_scrolled_distance;
	Vector2f smoothscroll_accumulated_fractional_distance;

	Vector2f inertia_scroll_velocity;
};

} // namespace Rml