PixelPaint: Let PickerTool optionally sample all layers

Previously, only the color from the selected layer would be picked.
Now, we allow the user to select if they want to sample the color
from all layers.

Userland/Applications/PixelPaint/Image.cpp

@@ -532,4 +532,19 @@ void Image::crop(Gfx::IntRect const& cropped_rect)
     did_change_rect(cropped_rect);
 }
 
+Color Image::color_at(Gfx::IntPoint const& point) const
+{
+    Color color;
+    for (auto& layer : m_layers) {
+        if (!layer.is_visible() || !layer.rect().contains(point))
+            continue;
+
+        auto layer_color = layer.bitmap().get_pixel(point);
+        float layer_opacity = layer.opacity_percent() / 100.0f;
+        layer_color.set_alpha((u8)(layer_color.alpha() * layer_opacity));
+        color = color.blend(layer_color);
+    }
+    return color;
+}
+
 }

Userland/Applications/PixelPaint/Image.h

@@ -103,6 +103,8 @@ public:
     void rotate(Gfx::RotationDirection direction);
     void crop(Gfx::IntRect const& rect);
 
+    Color color_at(Gfx::IntPoint const& point) const;
+
 private:
     explicit Image(Gfx::IntSize const&);
 

Userland/Applications/PixelPaint/PickerTool.cpp

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2021, Mustafa Quraish <mustafa@cs.toronto.edu>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -7,6 +8,8 @@
 #include "PickerTool.h"
 #include "ImageEditor.h"
 #include "Layer.h"
+#include <LibGUI/BoxLayout.h>
+#include <LibGUI/CheckBox.h>
 
 namespace PixelPaint {
 
@@ -20,17 +23,41 @@ PickerTool::~PickerTool()
 
 void PickerTool::on_mousedown(Layer* layer, MouseEvent& event)
 {
-    if (!layer)
+    auto& position = event.layer_event().position();
+
+    Color color;
+    if (m_sample_all_layers) {
+        color = m_editor->image().color_at(position);
+    } else {
+        if (!layer || !layer->rect().contains(position))
+            return;
+        color = layer->bitmap().get_pixel(position);
+    }
+
+    // We picked a transparent pixel, do nothing.
+    if (!color.alpha())
         return;
 
-    auto& layer_event = event.layer_event();
-    if (!layer->rect().contains(layer_event.position()))
-        return;
-    auto color = layer->bitmap().get_pixel(layer_event.position());
-    if (layer_event.button() == GUI::MouseButton::Left)
+    if (event.layer_event().button() == GUI::MouseButton::Left)
         m_editor->set_primary_color(color);
-    else if (layer_event.button() == GUI::MouseButton::Right)
+    else if (event.layer_event().button() == GUI::MouseButton::Right)
         m_editor->set_secondary_color(color);
 }
 
+GUI::Widget* PickerTool::get_properties_widget()
+{
+    if (!m_properties_widget) {
+        m_properties_widget = GUI::Widget::construct();
+        m_properties_widget->set_layout<GUI::VerticalBoxLayout>();
+
+        auto& sample_checkbox = m_properties_widget->add<GUI::CheckBox>("Sample all layers");
+        sample_checkbox.set_checked(m_sample_all_layers);
+        sample_checkbox.on_checked = [&](bool value) {
+            m_sample_all_layers = value;
+        };
+    }
+
+    return m_properties_widget.ptr();
+}
+
 }

Userland/Applications/PixelPaint/PickerTool.h

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2021, Mustafa Quraish <mustafa@cs.toronto.edu>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -16,7 +17,13 @@ public:
     virtual ~PickerTool() override;
 
     virtual void on_mousedown(Layer*, MouseEvent&) override;
+
+    virtual GUI::Widget* get_properties_widget() override;
     virtual Gfx::StandardCursor cursor() override { return Gfx::StandardCursor::Eyedropper; }
+
+private:
+    RefPtr<GUI::Widget> m_properties_widget;
+    bool m_sample_all_layers { false };
 };
 
 }