LibGUI: Add a GItemView class.

This is a GAbstractView subclass that implements a icon-based view onto
a GModel. It still need a bunch of work, but it's in basic usable shape.

LibGUI/GItemView.cpp

@@ -0,0 +1,199 @@
+#include <LibGUI/GItemView.h>
+#include <LibGUI/GModel.h>
+#include <LibGUI/GScrollBar.h>
+#include <SharedGraphics/Painter.h>
+#include <Kernel/KeyCode.h>
+
+GItemView::GItemView(GWidget* parent)
+    : GAbstractView(parent)
+{
+}
+
+GItemView::~GItemView()
+{
+}
+
+void GItemView::scroll_into_view(const GModelIndex& index, Orientation orientation)
+{
+    GScrollableWidget::scroll_into_view(item_rect(index.row()), orientation);
+}
+
+void GItemView::resize_event(GResizeEvent& event)
+{
+    GAbstractView::resize_event(event);
+    update_content_size();
+}
+
+void GItemView::did_update_model()
+{
+    GAbstractView::did_update_model();
+    update_content_size();
+    update();
+}
+
+void GItemView::update_content_size()
+{
+    if (!model())
+        return set_content_size({ });
+
+    m_visual_column_count = available_size().width() / effective_item_size().width();
+    if (m_visual_column_count)
+        m_visual_row_count = ceil_div(model()->row_count(), m_visual_column_count);
+    else
+        m_visual_row_count = 0;
+
+    int content_width = available_size().width();
+    int content_height = m_visual_row_count * effective_item_size().height();
+
+    set_content_size({ content_width, content_height });
+}
+
+Rect GItemView::item_rect(int item_index) const
+{
+    if (!m_visual_row_count || !m_visual_column_count)
+        return { };
+    int visual_row_index = item_index / m_visual_column_count;
+    int visual_column_index = item_index % m_visual_column_count;
+    return {
+        visual_column_index * effective_item_size().width(),
+        visual_row_index * effective_item_size().height(),
+        effective_item_size().width(),
+        effective_item_size().height()
+    };
+}
+
+void GItemView::mousedown_event(GMouseEvent& event)
+{
+    if (event.button() == GMouseButton::Left) {
+        // FIXME: Since all items are the same size, just compute the clicked item index
+        //        instead of iterating over everything.
+        auto adjusted_position = event.position().translated(0, vertical_scrollbar().value());
+        for (int i = 0; i < item_count(); ++i) {
+            if (item_rect(i).contains(adjusted_position)) {
+                model()->set_selected_index({ i, 0 });
+                update();
+                return;
+            }
+        }
+        model()->set_selected_index({ });
+        update();
+    }
+}
+
+void GItemView::paint_event(GPaintEvent& event)
+{
+    Painter painter(*this);
+    painter.set_clip_rect(event.rect());    
+    painter.fill_rect(event.rect(), Color::White);
+    painter.save();
+    painter.translate(-horizontal_scrollbar().value(), -vertical_scrollbar().value());
+
+    auto column_metadata = model()->column_metadata(m_model_column);
+    const Font& font = column_metadata.font ? *column_metadata.font : this->font();
+
+    for (int item_index = 0; item_index < model()->row_count(); ++item_index) {
+        bool is_selected_item = item_index == model()->selected_index().row();
+        Color background_color;
+        if (is_selected_item) {
+            background_color = is_focused() ? Color::from_rgb(0x84351a) : Color::from_rgb(0x606060);
+        } else {
+            background_color = Color::White;
+        }
+
+        Rect item_rect = this->item_rect(item_index);
+        GModelIndex model_index(item_index, m_model_column);
+
+        auto icon = model()->data(model_index, GModel::Role::Icon);
+        auto item_text = model()->data(model_index, GModel::Role::Display);
+
+        Rect icon_rect = { 0, 0, 32, 32 };
+        icon_rect.center_within(item_rect);
+        icon_rect.move_by(0, -font.glyph_height() - 6);
+
+        if (icon.is_bitmap()) {
+            painter.draw_scaled_bitmap(icon_rect, icon.as_bitmap(), icon.as_bitmap().rect());
+        }
+
+        Rect text_rect { 0, icon_rect.bottom() + 6 + 1, font.width(item_text.to_string()), font.glyph_height() };
+        text_rect.center_horizontally_within(item_rect);
+        text_rect.inflate(4, 4);
+
+        Color text_color;
+        if (is_selected_item)
+            text_color = Color::White;
+        else
+            text_color = model()->data(model_index, GModel::Role::ForegroundColor).to_color(Color::Black);
+        painter.fill_rect(text_rect, background_color);
+        painter.draw_text(text_rect, item_text.to_string(), font, TextAlignment::Center, text_color);
+    };
+
+    painter.restore();
+
+    if (is_focused())
+        painter.draw_rect({ { }, available_size() }, Color::from_rgb(0x84351a));
+}
+
+int GItemView::item_count() const
+{
+    if (!model())
+        return 0;
+    return model()->row_count();
+}
+
+void GItemView::keydown_event(GKeyEvent& event)
+{
+    if (!model())
+        return;
+    auto& model = *this->model();
+    if (event.key() == KeyCode::Key_Return) {
+        model.activate(model.selected_index());
+        return;
+    }
+    if (event.key() == KeyCode::Key_Up) {
+        GModelIndex new_index;
+        if (model.selected_index().is_valid())
+            new_index = { model.selected_index().row() - 1, model.selected_index().column() };
+        else
+            new_index = { 0, 0 };
+        if (model.is_valid(new_index)) {
+            model.set_selected_index(new_index);
+            scroll_into_view(new_index, Orientation::Vertical);
+            update();
+        }
+        return;
+    }
+    if (event.key() == KeyCode::Key_Down) {
+        GModelIndex new_index;
+        if (model.selected_index().is_valid())
+            new_index = { model.selected_index().row() + 1, model.selected_index().column() };
+        else
+            new_index = { 0, 0 };
+        if (model.is_valid(new_index)) {
+            model.set_selected_index(new_index);
+            scroll_into_view(new_index, Orientation::Vertical);
+            update();
+        }
+        return;
+    }
+    if (event.key() == KeyCode::Key_PageUp) {
+        int items_per_page = visible_content_rect().height() / effective_item_size().height();
+        GModelIndex new_index(max(0, model.selected_index().row() - items_per_page), model.selected_index().column());
+        if (model.is_valid(new_index)) {
+            model.set_selected_index(new_index);
+            scroll_into_view(new_index, Orientation::Vertical);
+            update();
+        }
+        return;
+    }
+    if (event.key() == KeyCode::Key_PageDown) {
+        int items_per_page = visible_content_rect().height() / effective_item_size().height();
+        GModelIndex new_index(min(model.row_count() - 1, model.selected_index().row() + items_per_page), model.selected_index().column());
+        if (model.is_valid(new_index)) {
+            model.set_selected_index(new_index);
+            scroll_into_view(new_index, Orientation::Vertical);
+            update();
+        }
+        return;
+    }
+    return GWidget::keydown_event(event);
+}