scroll_aperture_widget.hpp

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// Copyright Take Vos 2022.
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE_1_0.txt or copy at https://www.boost.org/LICENSE_1_0.txt)
 
#pragma once
 
#include "widget.hpp"
 
namespace hi { inline namespace v1 {
 
class scroll_aperture_widget : public widget {
public:
    using super = widget;
 
    observer<float> content_width;
    observer<float> content_height;
    observer<float> aperture_width;
    observer<float> aperture_height;
    observer<float> offset_x;
    observer<float> offset_y;
 
    scroll_aperture_widget(gui_window& window, widget *parent) noexcept : super(window, parent)
    {
        hi_axiom(is_gui_thread());
        hi_axiom(parent);
 
        // The aperture-widget will not draw itself, only its selected content.
        semantic_layer = parent->semantic_layer;
 
        // clang-format off
        _content_width_cbt = content_width.subscribe([&](auto...){ request_relayout(); });
        _content_height_cbt = content_height.subscribe([&](auto...){ request_relayout(); });
        _aperture_width_cbt = aperture_width.subscribe([&](auto...){ request_relayout(); });
        _aperture_height_cbt = aperture_height.subscribe([&](auto...){ request_relayout(); });
        _offset_x_cbt = offset_x.subscribe([&](auto...){ request_relayout(); });
        _offset_y_cbt = offset_y.subscribe([&](auto...){ request_relayout(); });
        // clang-format off
    }
 
    template<typename Widget, typename... Args>
    Widget &make_widget(Args &&...args) noexcept
    {
        hi_axiom(is_gui_thread());
        hi_axiom(not _content);
 
        auto tmp = std::make_unique<Widget>(window, this, std::forward<Args>(args)...);
        auto &ref = *tmp;
        _content = std::move(tmp);
        return ref;
    }
 
    [[nodiscard]] bool x_axis_scrolls() const noexcept
    {
        return *content_width > *aperture_width;
    }
 
    [[nodiscard]] bool y_axis_scrolls() const noexcept
    {
        return *content_height > *aperture_height;
    }
 
    [[nodiscard]] generator<widget *> children() const noexcept override
    {
        co_yield _content.get();
    }
 
    widget_constraints const &set_constraints() noexcept override
    {
        _layout = {};
 
        hi_axiom(_content);
        hilet content_constraints = _content->set_constraints();
 
        hilet minimum_size = extent2{
            content_constraints.margins.left() + content_constraints.minimum.width() + content_constraints.margins.right(),
            content_constraints.margins.top() + content_constraints.minimum.height() + content_constraints.margins.bottom()};
        hilet preferred_size = extent2{
            content_constraints.margins.left() + content_constraints.preferred.width() + content_constraints.margins.right(),
            content_constraints.margins.top() + content_constraints.preferred.height() + content_constraints.margins.bottom()};
        hilet maximum_size = extent2{
            content_constraints.margins.left() + content_constraints.maximum.width() + content_constraints.margins.right(),
            content_constraints.margins.top() + content_constraints.maximum.height() + content_constraints.margins.bottom()};
 
        return _constraints = {minimum_size, preferred_size, maximum_size, margins{}};
    }
 
    void set_layout(widget_layout const &layout) noexcept override
    {
        hilet content_constraints = _content->constraints();
        hilet margins = content_constraints.margins;
 
        if (compare_store(_layout, layout)) {
            hilet preferred_size = content_constraints.preferred;
 
            aperture_width = layout.width() - margins.left() - margins.right();
            aperture_height = layout.height() - margins.bottom() - margins.top();
 
            // Start scrolling with the preferred size as minimum, so
            // that widgets in the content don't get unnecessarily squeezed.
            content_width = *aperture_width < preferred_size.width() ? preferred_size.width() : *aperture_width;
            content_height = *aperture_height < preferred_size.height() ? preferred_size.height() : *aperture_height;
        }
 
        // Make sure the offsets are limited to the scrollable area.
        hilet offset_x_max = std::max(*content_width - *aperture_width, 0.0f);
        hilet offset_y_max = std::max(*content_height - *aperture_height, 0.0f);
        offset_x = std::clamp(std::round(*offset_x), 0.0f, offset_x_max);
        offset_y = std::clamp(std::round(*offset_y), 0.0f, offset_y_max);
 
        // The position of the content rectangle relative to the scroll view.
        // The size is further adjusted if the either the horizontal or vertical scroll bar is invisible.
        _content_rectangle = {
            -*offset_x + margins.left(), -*offset_y + margins.bottom(), *content_width, *content_height};
 
        // The content needs to be at a higher elevation, so that hitbox check
        // will work correctly for handling scrolling with mouse wheel.
        _content->set_layout(layout.transform(_content_rectangle, 1.0f, layout.rectangle()));
    }
 
    void draw(draw_context const &context) noexcept
    {
        if (*mode > widget_mode::invisible) {
            _content->draw(context);
        }
    }
 
    [[nodiscard]] hitbox hitbox_test(point3 position) const noexcept override
    {
        hi_axiom(is_gui_thread());
 
        if (*mode >= widget_mode::partial) {
            auto r = _content->hitbox_test_from_parent(position);
 
            if (layout().contains(position)) {
                r = std::max(r, hitbox{this, position});
            }
            return r;
 
        } else {
            return {};
        }
    }
 
    bool handle_event(gui_event const &event) noexcept override
    {
        hi_axiom(is_gui_thread());
 
        if (event == gui_event_type::mouse_wheel) {
            hilet new_offset_x = *offset_x + event.mouse().wheel_delta.x() * theme().scale;
            hilet new_offset_y = *offset_y + event.mouse().wheel_delta.y() * theme().scale;
            hilet max_offset_x = std::max(0.0f, *content_width - *aperture_width);
            hilet max_offset_y = std::max(0.0f, *content_height - *aperture_height);
 
            offset_x = std::clamp(new_offset_x, 0.0f, max_offset_x);
            offset_y = std::clamp(new_offset_y, 0.0f, max_offset_y);
            request_relayout();
            return true;
        } else {
            return super::handle_event(event);
        }
    }
 
    void scroll_to_show(hi::aarectangle to_show) noexcept override
    {
        auto safe_rectangle = intersect(_layout.rectangle(), _layout.clipping_rectangle);
        float delta_x = 0.0f;
        float delta_y = 0.0f;
 
        if (safe_rectangle.width() > theme().margin and safe_rectangle.height() > theme().margin) {
            // This will look visually better, if the selected widget is moved with some margin from
            // the edge of the scroll widget. The margins of the content do not have anything to do
            // with the margins that are needed here.
            safe_rectangle = safe_rectangle - theme().margin;
 
            if (to_show.right() > safe_rectangle.right()) {
                delta_x = to_show.right() - safe_rectangle.right();
            } else if (to_show.left() < safe_rectangle.left()) {
                delta_x = to_show.left() - safe_rectangle.left();
            }
 
            if (to_show.top() > safe_rectangle.top()) {
                delta_y = to_show.top() - safe_rectangle.top();
            } else if (to_show.bottom() < safe_rectangle.bottom()) {
                delta_y = to_show.bottom() - safe_rectangle.bottom();
            }
 
            // Scroll the widget
            offset_x += delta_x;
            offset_y += delta_y;
        }
 
        // There may be recursive scroll view, and they all need to move until the rectangle is visible.
        if (parent) {
            parent->scroll_to_show(bounding_rectangle(_layout.to_parent * translate2(delta_x, delta_y) * to_show));
        }
    }
private:
    aarectangle _content_rectangle;
    std::unique_ptr<widget> _content;
    decltype(content_width)::callback_token _content_width_cbt;
    decltype(content_height)::callback_token _content_height_cbt;
    decltype(aperture_width)::callback_token _aperture_width_cbt;
    decltype(aperture_height)::callback_token _aperture_height_cbt;
    decltype(offset_x)::callback_token _offset_x_cbt;
    decltype(offset_y)::callback_token _offset_y_cbt;
};
 
}} // namespace hi::inline v1