PaintBrush: Start refactoring to support layer-based images

The main editing widget is now the new ImageEditor widget, which works
on an Image object, which internally has a stack of Layer objects.

Layers are composited back-to-front when painting the Image inside an
ImageEditor.

Applications/PaintBrush/Image.cpp

@@ -0,0 +1,66 @@
+/*
+ * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "Image.h"
+#include "Layer.h"
+#include <LibGUI/Painter.h>
+
+namespace PaintBrush {
+
+RefPtr<Image> Image::create_with_size(const Gfx::Size& size)
+{
+    if (size.is_empty())
+        return nullptr;
+
+    if (size.width() > 16384 || size.height() > 16384)
+        return nullptr;
+
+    return adopt(*new Image(size));
+}
+
+Image::Image(const Gfx::Size& size)
+    : m_size(size)
+{
+}
+
+void Image::paint_into(GUI::Painter& painter, const Gfx::Rect& dest_rect, const Gfx::Rect& src_rect)
+{
+    for (auto& layer : m_layers) {
+        auto target = dest_rect.translated(layer.location());
+        dbg() << "Composite layer " << layer.name() << " target: " << target << ", src_rect: " << src_rect;
+        painter.draw_scaled_bitmap(target, layer.bitmap(), src_rect);
+    }
+}
+
+void Image::add_layer(NonnullRefPtr<Layer> layer)
+{
+    for (auto& existing_layer : m_layers) {
+        ASSERT(&existing_layer != layer.ptr());
+    }
+    m_layers.append(move(layer));
+}
+
+}