PixelPaint: Add `Merge Active Layer Down` action

This allows you to merge the active layer with the one below it.

3 files changed, 33 insertions, 0 deletions

diff --git a/Userland/Applications/PixelPaint/Image.cpp b/Userland/Applications/PixelPaint/Image.cpp
index 6f3676fa9a..271800c374 100644
--- a/Userland/Applications/PixelPaint/Image.cpp
+++ b/Userland/Applications/PixelPaint/Image.cpp
@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2020-2021, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2021, Mustafa Quraish <mustafa@cs.toronto.edu>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -483,6 +484,23 @@ void Image::merge_visible_layers()
     }
 }
 
+void Image::merge_active_layer_down(Layer& layer)
+{
+    if (m_layers.size() < 2)
+        return;
+    int layer_index = this->index_of(layer);
+    if (layer_index == 0) {
+        dbgln("Cannot merge layer down: layer is already at the bottom");
+        return; // FIXME: Notify user of error properly.
+    }
+
+    auto& layer_below = m_layers.at(layer_index - 1);
+    GUI::Painter painter(layer_below.bitmap());
+    painter.draw_scaled_bitmap(rect(), layer.bitmap(), layer.rect(), (float)layer.opacity_percent() / 100.0f);
+    remove_layer(layer);
+    select_layer(&layer_below);
+}
+
 void Image::select_layer(Layer* layer)
 {
     for (auto* client : m_clients)
diff --git a/Userland/Applications/PixelPaint/Image.h b/Userland/Applications/PixelPaint/Image.h
index f4c693d5e3..cefd0551e3 100644
--- a/Userland/Applications/PixelPaint/Image.h
+++ b/Userland/Applications/PixelPaint/Image.h
@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2020-2021, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2021, Mustafa Quraish <mustafa@cs.toronto.edu>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -74,6 +75,7 @@ public:
     void select_layer(Layer*);
     void flatten_all_layers();
     void merge_visible_layers();
+    void merge_active_layer_down(Layer& layer);
 
     void add_client(ImageClient&);
     void remove_client(ImageClient&);
diff --git a/Userland/Applications/PixelPaint/main.cpp b/Userland/Applications/PixelPaint/main.cpp
index 246e7ddaa9..dc82695dfd 100644
--- a/Userland/Applications/PixelPaint/main.cpp
+++ b/Userland/Applications/PixelPaint/main.cpp
@@ -541,6 +541,19 @@ int main(int argc, char** argv)
         },
         window));
 
+    layer_menu.add_action(GUI::Action::create(
+        "M&erge Active Layer Down", { Mod_Ctrl, Key_E }, [&](auto&) {
+            auto* editor = current_image_editor();
+            if (!editor)
+                return;
+            auto active_layer = editor->active_layer();
+            if (!active_layer)
+                return;
+            editor->image().merge_active_layer_down(*active_layer);
+            editor->did_complete_action();
+        },
+        window));
+
     auto& filter_menu = window->add_menu("&Filter");
     auto& spatial_filters_menu = filter_menu.add_submenu("&Spatial");