donner::svg::compositor::DragSession Class Reference

RAII session for a drag interaction with composited rendering. More...

#include "donner/svg/compositor/DragSession.h"

Public Member Functions
	~DragSession ()
	Destructor. Demotes the target entity if the session is still active.
	DragSession (const DragSession &)=delete
DragSession &	operator= (const DragSession &)=delete
	DragSession (DragSession &&other) noexcept
	Transfer ownership of an active drag promotion.
DragSession &	operator= (DragSession &&other) noexcept
	End this session's promotion and take ownership of another's.
Entity	target () const
	Returns the target entity being dragged.
bool	isActive () const
	Returns true if this session is still active (entity is promoted).
void	end ()
	Explicitly end the drag session, demoting the entity.

Static Public Member Functions
static std::optional< DragSession >	begin (CompositorController &compositor, Entity target)
	Begin a drag session by promoting the target entity.

Detailed Description

RAII session for a drag interaction with composited rendering.

Promotes the target entity on construction and demotes it on destruction, ensuring the compositor layer lifecycle is tied to the drag gesture. Callers mutate the entity's DOM transform directly during the drag; the compositor's fast path (renderFrame) picks up pure-translation deltas and reuses the cached bitmap without re-rasterizing.

Usage:

// On pointer-down / drag start:
auto drag = DragSession::begin(compositor, hitEntity);
if (!drag) { return; }  // promotion failed, fall back to full re-render
 
// On pointer-move:
element.setTransform(Transform2d::Translate(currentPos - startPos) * startTransform);
compositor.renderFrame(viewport);
 
// On pointer-up / drag end:
drag.reset();  // or let it fall out of scope
compositor.renderFrame(viewport);  // re-render with entity settled at new DOM position

Constructor & Destructor Documentation

DragSession()

donner::svg::compositor::DragSession::DragSession ( DragSession && other )

noexcept

Transfer ownership of an active drag promotion.

Parameters

other

Session whose promotion is transferred.

Member Function Documentation

begin()

std::optional< DragSession > donner::svg::compositor::DragSession::begin ( CompositorController & compositor, Entity target )

static

Begin a drag session by promoting the target entity.

Parameters

compositor	The compositor controller managing layers.
target	The entity to drag.

Returns

A DragSession if promotion succeeded, or std::nullopt if the entity could not be promoted (invalid entity, layer limit reached, etc.).

operator=()

DragSession & donner::svg::compositor::DragSession::operator= ( DragSession && other )

noexcept

End this session's promotion and take ownership of another's.

Parameters

other

Session whose promotion is transferred.

Returns

This session after the transfer.

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The documentation for this class was generated from the following file:

• donner/svg/compositor/DragSession.h