indicator()

Scrollable & MayaFlux::Portal::Forma::Scrollable::indicator	(	Surface &	surface,
		Mapped< glm::vec2 >	el,
		Kinesis::AABB2D	track
	)

Attach a caller-built element as a live, draggable scroll indicator.

Scrollable draws nothing itself. Build whatever Mapped<glm::vec2> your own geometry function produces - a bar, a squiggle, a sampled texture, anything computable from (position_frac, extent_frac) - via Portal::Forma::create<glm::vec2>, register it, and hand it here. position_frac is 0 at the top of content_bounds and 1 at the fully scrolled bottom; extent_frac is the viewport/content height ratio (how much of the content is visible at once), so a geometry function can size its own drawing without asking Scrollable anything further.

On every scroll - wheel (place()'s default wiring), scroll_by(), or dragging this same element - the live fraction pair is written to el.state and el.sync() is called, the same "call sync() straight from the handler that changed the value, no polling" idiom Collapsible's own on_press already uses. track() also refreshes extent_frac (without a Layer, so el's hit region only, not bounds_hint, can lag very slightly until the next scroll - self-corrects on the first interaction after).

Also wires on_drag on el.element.id: dragging maps the cursor's NDC y absolutely onto content offset within track, the same inverse-mapping idiom Geometry::vertical_fader uses for its own handle, routed through scroll_by() so drag and wheel scrolling stay in sync through one path. No handle-size compensation is applied, unlike vertical_fader - an indicator has no fixed rendered size for Scrollable to know about.

Parameters

surface	Surface owning the same Layer/Context place() used.
el	Caller's Mapped<glm::vec2>, already registered on surface's Layer.
track	NDC region the drag is measured against; its full height maps to the full scrollable range.

Returns

*this, for chaining - see track()'s

.

Definition at line 140 of file Scrollable.cpp.

{
    if (!scroll || !offset || !m_tracked || !m_indicator)
        return *this;
 
    *m_indicator = std::move(el);
    m_indicator->state->write(scroll_extent(*scroll));
    m_indicator->sync(&surface.layer());
 
    auto scroll_state = scroll;
    auto scroll_offset = offset;
    auto tracked = m_tracked;
    auto ind = m_indicator;
 
    surface.ctx().on_drag(ind->element.id, IO::MouseButtons::Left,
        [scroll_state, scroll_offset, tracked, ind, surface, track](uint32_t, glm::vec2 ndc) mutable {
            const float max_offset_y = std::max(0.F,
                scroll_state->content_bounds.height() - scroll_state->viewport_bounds.height());
            if (max_offset_y <= 0.F)
                return;
 
            const float frac = std::clamp((track.max.y - ndc.y) / track.height(), 0.F, 1.F);
            const float target = frac * max_offset_y;
 
            Kinesis::apply_scroll(*scroll_state, { 0.F, target - scroll_state->offset.y });
            reflow(*scroll_state, *scroll_offset, *tracked, surface.layer(), ind.get());
        });
 
    return *this;
}

References MayaFlux::Portal::Forma::Surface::ctx(), MayaFlux::Portal::Forma::Layer::get(), MayaFlux::Portal::Forma::Surface::layer(), MayaFlux::IO::Left, m_indicator, m_tracked, offset, MayaFlux::Portal::Forma::Context::on_drag(), scroll, and track().

Referenced by wheel_handler().

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