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/Slide.cpp

@@ -0,0 +1,53 @@
+/*
+ * Copyright (c) 2022, kleines Filmröllchen <filmroellchen@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "Slide.h"
+#include <AK/JsonObject.h>
+#include <AK/NonnullRefPtrVector.h>
+#include <LibGUI/Window.h>
+#include <LibGfx/Painter.h>
+#include <LibGfx/Size.h>
+#include <LibGfx/TextAlignment.h>
+
+Slide::Slide(NonnullRefPtrVector<SlideObject> slide_objects, String title)
+    : m_slide_objects(move(slide_objects))
+    , m_title(move(title))
+{
+}
+
+ErrorOr<Slide> Slide::parse_slide(JsonObject const& slide_json, NonnullRefPtr<GUI::Window> window)
+{
+    // FIXME: Use the text with the "title" role for a title, if there is no title given.
+    auto title = slide_json.get("title"sv).as_string_or("Untitled slide");
+
+    auto const& maybe_slide_objects = slide_json.get("objects"sv);
+    if (!maybe_slide_objects.is_array())
+        return Error::from_string_view("Slide objects must be an array"sv);
+
+    auto const& json_slide_objects = maybe_slide_objects.as_array();
+    NonnullRefPtrVector<SlideObject> slide_objects;
+    for (auto const& maybe_slide_object_json : json_slide_objects.values()) {
+        if (!maybe_slide_object_json.is_object())
+            return Error::from_string_view("Slides must be objects"sv);
+        auto const& slide_object_json = maybe_slide_object_json.as_object();
+
+        auto slide_object = TRY(SlideObject::parse_slide_object(slide_object_json, window));
+        slide_objects.append(move(slide_object));
+    }
+
+    return Slide { move(slide_objects), title };
+}
+
+void Slide::paint(Gfx::Painter& painter, unsigned int current_frame, Gfx::FloatSize display_scale) const
+{
+    for (auto const& object : m_slide_objects) {
+        if (object.is_visible_during_frame(current_frame))
+            object.paint(painter, display_scale);
+    }
+
+    // FIXME: Move this to user settings.
+    painter.draw_text(painter.clip_rect(), title(), Gfx::TextAlignment::BottomCenter);
+}