func (a *App) SetFrameCallback(cb FrameCallback) {
	if a.window == nil {
		return
	}
	a.window.frameCallback = cb
}

type FrameStats struct {
	// FrameStart is the time when Frame() was called.
	FrameStart	time.Time

	// LayoutDuration is how long the layout pass took.
	// Zero if layout was not performed this frame.
	LayoutDuration	time.Duration

	// DrawDuration is how long the draw pass took.
	DrawDuration	time.Duration

	// TotalDuration is the total time spent in Frame().
	TotalDuration	time.Duration

	// LayoutPerformed indicates whether layout was recalculated this frame.
	LayoutPerformed	bool

	// DrawSkipped indicates that the draw pass was skipped because no
	// widgets in the tree needed re-rendering. When true, the host
	// application can reuse the previous frame's GPU framebuffer output.
	//
	// This is the primary retained-mode optimization: idle UIs skip
	// rendering entirely, consuming zero CPU for the draw phase.
	DrawSkipped	bool

	// DrawStats provides per-widget statistics from the draw traversal.
	//
	// When DrawSkipped is true, DrawStats is zero-valued (no traversal
	// was performed). When DrawSkipped is false, DrawStats shows how many
	// widgets were drawn, how many were dirty vs clean, and how many were
	// skipped due to invisibility.
	//
	// This is primarily useful for performance monitoring and for
	// validating that the retained-mode dirty-tracking system is
	// working correctly.
	DrawStats	widget.DrawStats
}