PixelPaint: Limit editing tools to selection

This effectively creates a double-buffer for tools to use when modifying
the layer's bitmap (content or mask). Once the changes have been made
the tool reports to the layer that it has made changes along with a Rect
of the changed region. The layer will then merge the changes from the
scratch image to the real bitmap. This merge is done as follows: If a
given pixel is inside the selected region, the pixel from the scratch
bitmap is copied to the real bitmap. If the pixel is not inside the
selected region, the pixel from the real bitmap is copied to the scratch
bitmap.

As an optimization, when there is no selection active, the new method
for getting the scratch bitmap will return the real bitmap and no
merging will need to take place.

8 files changed, 51 insertions, 14 deletions

diff --git a/Userland/Applications/PixelPaint/Layer.cpp b/Userland/Applications/PixelPaint/Layer.cpp
index 3c8bab3035..6a8c38cb90 100644
--- a/Userland/Applications/PixelPaint/Layer.cpp
+++ b/Userland/Applications/PixelPaint/Layer.cpp
@@ -1,6 +1,7 @@
 /*
  * Copyright (c) 2020-2021, Andreas Kling <kling@serenityos.org>
  * Copyright (c) 2022, Tobias Christiansen <tobyase@serenityos.org>
+ * Copyright (c) 2022, Timothy Slater <tslater2006@gmail.com>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -65,6 +66,21 @@ Layer::Layer(Image& image, NonnullRefPtr<Gfx::Bitmap> bitmap, String name)
 
 void Layer::did_modify_bitmap(Gfx::IntRect const& rect)
 {
+    if (!m_scratch_edited_bitmap.is_null()) {
+        for (int y = 0; y < rect.height(); ++y) {
+            for (int x = 0; x < rect.width(); ++x) {
+                Gfx::IntPoint next_point = { rect.left() + x, rect.top() + y };
+                if (!m_scratch_edited_bitmap->rect().contains(next_point))
+                    continue;
+
+                if (this->image().selection().is_selected(next_point.translated(this->location())))
+                    currently_edited_bitmap().set_pixel(next_point, m_scratch_edited_bitmap->get_pixel(next_point));
+                else
+                    m_scratch_edited_bitmap->set_pixel(next_point, currently_edited_bitmap().get_pixel(next_point));
+            }
+        }
+    }
+
     m_image.layer_did_modify_bitmap({}, *this, rect);
     update_cached_bitmap();
 }
@@ -93,6 +109,21 @@ void Layer::set_name(String name)
     m_image.layer_did_modify_properties({}, *this);
 }
 
+Gfx::Bitmap& Layer::get_scratch_edited_bitmap()
+{
+    if (this->image().selection().is_empty()) {
+        m_scratch_edited_bitmap = nullptr;
+        return currently_edited_bitmap();
+    }
+
+    if (!m_scratch_edited_bitmap.is_null())
+        return *m_scratch_edited_bitmap;
+
+    m_scratch_edited_bitmap = MUST(currently_edited_bitmap().clone());
+
+    return *m_scratch_edited_bitmap;
+}
+
 RefPtr<Gfx::Bitmap> Layer::try_copy_bitmap(Selection const& selection) const
 {
     if (selection.is_empty()) {
@@ -158,6 +189,7 @@ ErrorOr<void> Layer::try_set_bitmaps(NonnullRefPtr<Gfx::Bitmap> content, RefPtr<
 
     m_content_bitmap = move(content);
     m_mask_bitmap = move(mask);
+    m_scratch_edited_bitmap = nullptr;
     update_cached_bitmap();
     return {};
 }
@@ -274,7 +306,7 @@ void Layer::set_edit_mode(Layer::EditMode mode)
 {
     if (m_edit_mode == mode)
         return;
-
+    m_scratch_edited_bitmap = nullptr;
     m_edit_mode = mode;
 }
 
diff --git a/Userland/Applications/PixelPaint/Layer.h b/Userland/Applications/PixelPaint/Layer.h
index a2996e24c0..6e5121ecee 100644
--- a/Userland/Applications/PixelPaint/Layer.h
+++ b/Userland/Applications/PixelPaint/Layer.h
@@ -2,6 +2,7 @@
  * Copyright (c) 2020-2021, Andreas Kling <kling@serenityos.org>
  * Copyright (c) 2022, the SerenityOS developers.
  * Copyright (c) 2022, Tobias Christiansen <tobyase@serenityos.org>
+ * Copyright (c) 2022, Timothy Slater <tslater2006@gmail.com>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -45,6 +46,7 @@ public:
     Gfx::Bitmap* mask_bitmap() { return m_mask_bitmap; }
 
     void create_mask();
+    Gfx::Bitmap& get_scratch_edited_bitmap();
 
     Gfx::IntSize size() const { return content_bitmap().size(); }
 
@@ -102,6 +104,7 @@ private:
     String m_name;
     Gfx::IntPoint m_location;
     NonnullRefPtr<Gfx::Bitmap> m_content_bitmap;
+    RefPtr<Gfx::Bitmap> m_scratch_edited_bitmap { nullptr };
     RefPtr<Gfx::Bitmap> m_mask_bitmap { nullptr };
     NonnullRefPtr<Gfx::Bitmap> m_cached_display_bitmap;
 
diff --git a/Userland/Applications/PixelPaint/Tools/BrushTool.cpp b/Userland/Applications/PixelPaint/Tools/BrushTool.cpp
index 802ebbc0d2..88568da916 100644
--- a/Userland/Applications/PixelPaint/Tools/BrushTool.cpp
+++ b/Userland/Applications/PixelPaint/Tools/BrushTool.cpp
@@ -29,7 +29,7 @@ void BrushTool::on_mousedown(Layer* layer, MouseEvent& event)
 
     // Shift+Click draws a line from the last position to current one.
     if (layer_event.shift() && m_has_clicked) {
-        draw_line(layer->currently_edited_bitmap(), color_for(layer_event), m_last_position, layer_event.position());
+        draw_line(layer->get_scratch_edited_bitmap(), color_for(layer_event), m_last_position, layer_event.position());
         auto modified_rect = Gfx::IntRect::from_two_points(m_last_position, layer_event.position()).inflated(m_size * 2, m_size * 2);
         layer->did_modify_bitmap(modified_rect);
         m_last_position = layer_event.position();
@@ -39,7 +39,7 @@ void BrushTool::on_mousedown(Layer* layer, MouseEvent& event)
     int const first_draw_opacity = 10;
 
     for (int i = 0; i < first_draw_opacity; ++i)
-        draw_point(layer->currently_edited_bitmap(), color_for(layer_event), layer_event.position());
+        draw_point(layer->get_scratch_edited_bitmap(), color_for(layer_event), layer_event.position());
 
     layer->did_modify_bitmap(Gfx::IntRect::centered_on(layer_event.position(), Gfx::IntSize { m_size * 2, m_size * 2 }));
     m_last_position = layer_event.position();
@@ -55,7 +55,7 @@ void BrushTool::on_mousemove(Layer* layer, MouseEvent& event)
     if (!(layer_event.buttons() & GUI::MouseButton::Primary || layer_event.buttons() & GUI::MouseButton::Secondary))
         return;
 
-    draw_line(layer->currently_edited_bitmap(), color_for(layer_event), m_last_position, layer_event.position());
+    draw_line(layer->get_scratch_edited_bitmap(), color_for(layer_event), m_last_position, layer_event.position());
 
     auto modified_rect = Gfx::IntRect::from_two_points(m_last_position, layer_event.position()).inflated(m_size * 2, m_size * 2);
 
diff --git a/Userland/Applications/PixelPaint/Tools/BucketTool.cpp b/Userland/Applications/PixelPaint/Tools/BucketTool.cpp
index 4cba2b9699..80228d5fc7 100644
--- a/Userland/Applications/PixelPaint/Tools/BucketTool.cpp
+++ b/Userland/Applications/PixelPaint/Tools/BucketTool.cpp
@@ -50,11 +50,11 @@ void BucketTool::on_mousedown(Layer* layer, MouseEvent& event)
     if (!layer->rect().contains(layer_event.position()))
         return;
 
-    GUI::Painter painter(layer->currently_edited_bitmap());
+    GUI::Painter painter(layer->get_scratch_edited_bitmap());
 
-    flood_fill(layer->currently_edited_bitmap(), layer_event.position(), m_editor->color_for(layer_event), m_threshold);
+    flood_fill(layer->get_scratch_edited_bitmap(), layer_event.position(), m_editor->color_for(layer_event), m_threshold);
 
-    layer->did_modify_bitmap();
+    layer->did_modify_bitmap(layer->get_scratch_edited_bitmap().rect());
     m_editor->did_complete_action(tool_name());
 }
 
diff --git a/Userland/Applications/PixelPaint/Tools/EllipseTool.cpp b/Userland/Applications/PixelPaint/Tools/EllipseTool.cpp
index a9256cb100..aa3b676843 100644
--- a/Userland/Applications/PixelPaint/Tools/EllipseTool.cpp
+++ b/Userland/Applications/PixelPaint/Tools/EllipseTool.cpp
@@ -84,10 +84,10 @@ void EllipseTool::on_mouseup(Layer* layer, MouseEvent& event)
         return;
 
     if (event.layer_event().button() == m_drawing_button) {
-        GUI::Painter painter(layer->currently_edited_bitmap());
+        GUI::Painter painter(layer->get_scratch_edited_bitmap());
         draw_using(painter, m_ellipse_start_position, m_ellipse_end_position, m_thickness);
         m_drawing_button = GUI::MouseButton::None;
-        layer->did_modify_bitmap();
+        layer->did_modify_bitmap(layer->get_scratch_edited_bitmap().rect());
         m_editor->update();
         m_editor->did_complete_action(tool_name());
     }
diff --git a/Userland/Applications/PixelPaint/Tools/LineTool.cpp b/Userland/Applications/PixelPaint/Tools/LineTool.cpp
index dbb12f3f3b..5aebf8b885 100644
--- a/Userland/Applications/PixelPaint/Tools/LineTool.cpp
+++ b/Userland/Applications/PixelPaint/Tools/LineTool.cpp
@@ -76,10 +76,11 @@ void LineTool::on_mouseup(Layer* layer, MouseEvent& event)
 
     auto& layer_event = event.layer_event();
     if (layer_event.button() == m_drawing_button) {
-        GUI::Painter painter(layer->currently_edited_bitmap());
+        GUI::Painter painter(layer->get_scratch_edited_bitmap());
         draw_using(painter, m_line_start_position, m_line_end_position, m_editor->color_for(m_drawing_button), m_thickness);
         m_drawing_button = GUI::MouseButton::None;
-        layer->did_modify_bitmap();
+        auto modified_rect = Gfx::IntRect::from_two_points(m_line_start_position, m_line_end_position).inflated(m_thickness * 2, m_thickness * 2);
+        layer->did_modify_bitmap(modified_rect);
         m_editor->update();
         m_editor->did_complete_action(tool_name());
     }
diff --git a/Userland/Applications/PixelPaint/Tools/RectangleTool.cpp b/Userland/Applications/PixelPaint/Tools/RectangleTool.cpp
index 44fe26ec5c..fb88922eef 100644
--- a/Userland/Applications/PixelPaint/Tools/RectangleTool.cpp
+++ b/Userland/Applications/PixelPaint/Tools/RectangleTool.cpp
@@ -87,10 +87,11 @@ void RectangleTool::on_mouseup(Layer* layer, MouseEvent& event)
         return;
 
     if (event.layer_event().button() == m_drawing_button) {
-        GUI::Painter painter(layer->currently_edited_bitmap());
+        GUI::Painter painter(layer->get_scratch_edited_bitmap());
         draw_using(painter, m_rectangle_start_position, m_rectangle_end_position, m_thickness, m_corner_radius);
         m_drawing_button = GUI::MouseButton::None;
-        layer->did_modify_bitmap();
+        auto modified_rect = Gfx::IntRect::from_two_points(m_rectangle_start_position, m_rectangle_end_position).inflated(m_thickness * 2, m_thickness * 2);
+        layer->did_modify_bitmap(modified_rect);
         m_editor->update();
         m_editor->did_complete_action(tool_name());
     }
diff --git a/Userland/Applications/PixelPaint/Tools/SprayTool.cpp b/Userland/Applications/PixelPaint/Tools/SprayTool.cpp
index 1118d6333f..a28bc03137 100644
--- a/Userland/Applications/PixelPaint/Tools/SprayTool.cpp
+++ b/Userland/Applications/PixelPaint/Tools/SprayTool.cpp
@@ -40,7 +40,7 @@ void SprayTool::paint_it()
     if (!layer)
         return;
 
-    auto& bitmap = layer->currently_edited_bitmap();
+    auto& bitmap = layer->get_scratch_edited_bitmap();
     GUI::Painter painter(bitmap);
     VERIFY(bitmap.bpp() == 32);
     double const minimal_radius = 2;