Applications: Add Presenter

This version can already:
- load all of the defined file format except for the image type and the
  frame-specific stuff
- navigate frames and slides (though frames are mostly stubbed out)
- display text with various common settings
- displays text with various fitting and scaling methods
- scale and position objects correctly no matter the window size

Userland/Applications/Presenter/Presentation.h

@@ -0,0 +1,60 @@
+/*
+ * Copyright (c) 2022, kleines Filmröllchen <filmroellchen@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include "Slide.h"
+#include <AK/Forward.h>
+#include <AK/HashMap.h>
+#include <AK/NonnullOwnPtr.h>
+#include <AK/String.h>
+#include <AK/Vector.h>
+#include <LibGfx/Painter.h>
+#include <LibGfx/Size.h>
+
+static constexpr int const PRESENTATION_FORMAT_VERSION = 1;
+
+// In-memory representation of the presentation stored in a file.
+// This class also contains all the parser code for loading .presenter files.
+class Presentation {
+public:
+    ~Presentation() = default;
+
+    // We can't pass this class directly in an ErrorOr because some of the components are not properly moveable under these conditions.
+    static ErrorOr<NonnullOwnPtr<Presentation>> load_from_file(StringView file_name, NonnullRefPtr<GUI::Window> window);
+
+    StringView title() const;
+    StringView author() const;
+    Gfx::IntSize normative_size() const { return m_normative_size; }
+
+    Slide const& current_slide() const { return m_slides[m_current_slide.value()]; }
+    unsigned current_slide_number() const { return m_current_slide.value(); }
+    unsigned current_frame_in_slide_number() const { return m_current_frame_in_slide.value(); }
+
+    void next_frame();
+    void previous_frame();
+    void go_to_first_slide();
+
+    // This assumes that the caller has clipped the painter to exactly the display area.
+    void paint(Gfx::Painter& painter) const;
+
+private:
+    static HashMap<String, String> parse_metadata(JsonObject const& metadata_object);
+    static ErrorOr<Gfx::IntSize> parse_presentation_size(JsonObject const& metadata_object);
+
+    Presentation(Gfx::IntSize normative_size, HashMap<String, String> metadata);
+    static NonnullOwnPtr<Presentation> construct(Gfx::IntSize normative_size, HashMap<String, String> metadata);
+
+    void append_slide(Slide slide);
+
+    Vector<Slide> m_slides {};
+    // This is not a pixel size, but an abstract size used by the slide objects for relative positioning.
+    Gfx::IntSize m_normative_size;
+    HashMap<String, String> m_metadata;
+
+    Checked<unsigned> m_current_slide { 0 };
+    Checked<unsigned> m_current_frame_in_slide { 0 };
+};