menu_view: support for displaying text selections

Similarly to the way of how a <cursor> can be defined for a <label>
widget, a selection can be expressed as follows:

  <label ...>
    <selection at="2" length="12"/>
  </label>

Issue #3607
Issue #3629

repos/gems/src/app/menu_view/label_widget.h

@@ -16,7 +16,7 @@
 
 /* local includes */
 #include <widget_factory.h>
-#include <cursor.h>
+#include <text_selection.h>
 
 namespace Menu_view { struct Label_widget; }
 
@@ -30,17 +30,22 @@ struct Menu_view::Label_widget : Widget, Cursor::Glyph_position
 	Text _text { };
 
 	Cursor::Model_update_policy         _cursor_update_policy;
+	Text_selection::Model_update_policy _selection_update_policy;
 
 	List_model<Cursor>         _cursors    { };
+	List_model<Text_selection> _selections { };
 
 	Label_widget(Widget_factory &factory, Xml_node node, Unique_id unique_id)
 	:
-		Widget(factory, node, unique_id), _cursor_update_policy(factory, *this)
+		Widget(factory, node, unique_id),
+		_cursor_update_policy(factory, *this),
+		_selection_update_policy(factory.alloc, *this)
 	{ }
 
 	~Label_widget()
 	{
-		_cursors.destroy_all_elements(_cursor_update_policy);
+		_cursors   .destroy_all_elements(_cursor_update_policy);
+		_selections.destroy_all_elements(_selection_update_policy);
 	}
 
 	void update(Xml_node node) override
@@ -49,7 +54,8 @@ struct Menu_view::Label_widget : Widget, Cursor::Glyph_position
 		_text = node.attribute_value("text", Text(""));
 		_text = Xml_unquoted(_text);
 
-		_cursors.update_from_xml(_cursor_update_policy, node);
+		_cursors   .update_from_xml(_cursor_update_policy,    node);
+		_selections.update_from_xml(_selection_update_policy, node);
 	}
 
 	Area min_size() const override
@@ -74,6 +80,9 @@ struct Menu_view::Label_widget : Widget, Cursor::Glyph_position
 
 		Point const centered = at + Point(dx/2, dy/2);
 
+		_selections.for_each([&] (Text_selection const &selection) {
+			selection.draw(pixel_surface, alpha_surface, at, text_size.h()); });
+
 		Text_painter::paint(pixel_surface,
 		                    Text_painter::Position(centered.x(), centered.y()),
 		                    *_font, Color(0, 0, 0), _text.string());

repos/gems/src/app/menu_view/text_selection.h

@@ -0,0 +1,125 @@
+/*
+ * \brief  Text selection
+ * \author Norman Feske
+ * \date   2020-01-15
+ */
+
+/*
+ * Copyright (C) 2020 Genode Labs GmbH
+ *
+ * This file is part of the Genode OS framework, which is distributed
+ * under the terms of the GNU Affero General Public License version 3.
+ */
+
+#ifndef _TEXT_SELECTION_H_
+#define _TEXT_SELECTION_H_
+
+/* Genode includes */
+#include <util/xml_generator.h>
+#include <util/list_model.h>
+
+/* local includes */
+#include <types.h>
+#include <widget_factory.h>
+#include <cursor.h>
+
+namespace Menu_view { struct Text_selection; }
+
+class Menu_view::Text_selection : List_model<Text_selection>::Element
+{
+	public:
+
+		using Glyph_position = Cursor::Glyph_position;
+
+	private:
+
+		friend class List_model<Text_selection>;
+		friend class List<Text_selection>;
+
+		Glyph_position &_glyph_position;
+
+		enum { NAME_MAX_LEN = 32 };
+		typedef String<NAME_MAX_LEN> Name;
+
+		Name const _name;
+
+		struct Range
+		{
+			unsigned xpos_px;
+			unsigned width_px;
+		};
+
+		Range _range { 0, 0 };
+
+		static Name _node_name(Xml_node node)
+		{
+			return node.attribute_value("name", Name(node.type()));
+		}
+
+		Range _range_from_xml_node(Xml_node node)
+		{
+			unsigned const at     = node.attribute_value("at",     0u),
+			               length = node.attribute_value("length", 0u);
+
+			unsigned const x1 = _glyph_position.xpos_of_glyph(at),
+			               x2 = _glyph_position.xpos_of_glyph(at + length);
+
+			unsigned const width = (x2 >= x1 ? x2 - x1 : 0);
+
+			return { .xpos_px = x1, .width_px = width };
+		}
+
+	public:
+
+		Text_selection(Xml_node node, Glyph_position &glyph_position)
+		:
+			_glyph_position(glyph_position), _name(_node_name(node))
+		{ }
+
+		void draw(Surface<Pixel_rgb888> &pixel_surface,
+		          Surface<Pixel_alpha8> &,
+		          Point at, unsigned height) const
+		{
+			Color const color(0xcf, 0x69, 0x69, 180);
+			Box_painter::paint(pixel_surface,
+			                   Rect(at + Point(_range.xpos_px, 0),
+			                        Area(_range.width_px, height)),
+			                   color);
+		}
+
+		struct Model_update_policy : List_model<Text_selection>::Update_policy
+		{
+			Allocator      &_alloc;
+			Glyph_position &_glyph_position;
+
+			Model_update_policy(Allocator &alloc, Glyph_position &glyph_position)
+			:
+				_alloc(alloc), _glyph_position(glyph_position)
+			{ }
+
+			void destroy_element(Text_selection &t) { destroy(_alloc, &t); }
+
+			Text_selection &create_element(Xml_node node)
+			{
+				return *new (_alloc)
+					Text_selection(node, _glyph_position);
+			}
+
+			void update_element(Text_selection &t, Xml_node node)
+			{
+				t._range = t._range_from_xml_node(node);
+			}
+
+			static bool element_matches_xml_node(Text_selection const &t, Xml_node node)
+			{
+				return node.has_type("selection") && _node_name(node) == t._name;
+			}
+
+			static bool node_is_element(Xml_node node)
+			{
+				return node.has_type("selection");
+			}
+		};
+};
+
+#endif /* _TEXT_SELECTION_ */