PixelPaint: Add "Brush Mode" to EraseTool :^)

Previously EraseTool would only let you have hard lines, similar
to PenTool. After inheriting from BrushTool in previous commits,
making the eraser (optionally) behave like a brush is much easier.

We only need to change how the colors are handled for the hardness,
which is why the `draw_point()` call is a bit more involved. Just
blending the colors doesn't work here since we actually want to
replace the previous color, unlike in BrushTool where we are just
layering the color on top.

2 files changed, 66 insertions, 4 deletions

diff --git a/Userland/Applications/PixelPaint/EraseTool.cpp b/Userland/Applications/PixelPaint/EraseTool.cpp
index 88f2cb3269..85b2130530 100644
--- a/Userland/Applications/PixelPaint/EraseTool.cpp
+++ b/Userland/Applications/PixelPaint/EraseTool.cpp
@@ -14,6 +14,7 @@
 #include <LibGUI/Label.h>
 #include <LibGUI/Menu.h>
 #include <LibGUI/Painter.h>
+#include <LibGUI/RadioButton.h>
 #include <LibGUI/ValueSlider.h>
 #include <LibGfx/Bitmap.h>
 
@@ -36,10 +37,26 @@ Color EraseTool::color_for(GUI::MouseEvent const&)
 
 void EraseTool::draw_point(Gfx::Bitmap& bitmap, Gfx::Color const& color, Gfx::IntPoint const& point)
 {
-    int radius = size() / 2;
-    Gfx::IntRect rect { point.x() - radius, point.y() - radius, size(), size() };
-    GUI::Painter painter(bitmap);
-    painter.clear_rect(rect, color);
+    if (m_draw_mode == DrawMode::Pencil) {
+        int radius = size() / 2;
+        Gfx::IntRect rect { point.x() - radius, point.y() - radius, size(), size() };
+        GUI::Painter painter(bitmap);
+        painter.clear_rect(rect, color);
+    } else {
+        for (int y = point.y() - size(); y < point.y() + size(); y++) {
+            for (int x = point.x() - size(); x < point.x() + size(); x++) {
+                auto distance = point.distance_from({ x, y });
+                if (x < 0 || x >= bitmap.width() || y < 0 || y >= bitmap.height())
+                    continue;
+                if (distance >= size())
+                    continue;
+                auto old_color = bitmap.get_pixel(x, y);
+                auto falloff = (1.0 - double { distance / size() }) * (1.0 / (100 - hardness()));
+                auto new_color = old_color.interpolate(color, falloff);
+                bitmap.set_pixel(x, y, new_color);
+            }
+        }
+    }
 }
 
 GUI::Widget* EraseTool::get_properties_widget()
@@ -65,6 +82,23 @@ GUI::Widget* EraseTool::get_properties_widget()
         };
         set_primary_slider(&size_slider);
 
+        auto& hardness_container = m_properties_widget->add<GUI::Widget>();
+        hardness_container.set_fixed_height(20);
+        hardness_container.set_layout<GUI::HorizontalBoxLayout>();
+
+        auto& hardness_label = hardness_container.add<GUI::Label>("Hardness:");
+        hardness_label.set_text_alignment(Gfx::TextAlignment::CenterLeft);
+        hardness_label.set_fixed_size(80, 20);
+
+        auto& hardness_slider = hardness_container.add<GUI::ValueSlider>(Orientation::Horizontal, "%");
+        hardness_slider.set_range(1, 99);
+        hardness_slider.set_value(hardness());
+
+        hardness_slider.on_change = [&](int value) {
+            set_hardness(value);
+        };
+        set_secondary_slider(&hardness_slider);
+
         auto& secondary_color_container = m_properties_widget->add<GUI::Widget>();
         secondary_color_container.set_fixed_height(20);
         secondary_color_container.set_layout<GUI::HorizontalBoxLayout>();
@@ -75,6 +109,29 @@ GUI::Widget* EraseTool::get_properties_widget()
         use_secondary_color_checkbox.on_checked = [&](bool checked) {
             m_use_secondary_color = checked;
         };
+
+        auto& mode_container = m_properties_widget->add<GUI::Widget>();
+        mode_container.set_fixed_height(46);
+        mode_container.set_layout<GUI::HorizontalBoxLayout>();
+        auto& mode_label = mode_container.add<GUI::Label>("Draw Mode:");
+        mode_label.set_text_alignment(Gfx::TextAlignment::CenterLeft);
+        mode_label.set_fixed_size(80, 20);
+
+        auto& mode_radio_container = mode_container.add<GUI::Widget>();
+        mode_radio_container.set_layout<GUI::VerticalBoxLayout>();
+        auto& pencil_mode_radio = mode_radio_container.add<GUI::RadioButton>("Pencil");
+        auto& brush_mode_radio = mode_radio_container.add<GUI::RadioButton>("Brush");
+
+        pencil_mode_radio.on_checked = [&](bool) {
+            m_draw_mode = DrawMode::Pencil;
+            hardness_slider.set_enabled(false);
+        };
+        brush_mode_radio.on_checked = [&](bool) {
+            m_draw_mode = DrawMode::Brush;
+            hardness_slider.set_enabled(true);
+        };
+
+        pencil_mode_radio.set_checked(true);
     }
 
     return m_properties_widget.ptr();
diff --git a/Userland/Applications/PixelPaint/EraseTool.h b/Userland/Applications/PixelPaint/EraseTool.h
index b8fa8a6ff2..6ae01225eb 100644
--- a/Userland/Applications/PixelPaint/EraseTool.h
+++ b/Userland/Applications/PixelPaint/EraseTool.h
@@ -28,6 +28,11 @@ protected:
 private:
     RefPtr<GUI::Widget> m_properties_widget;
 
+    enum class DrawMode {
+        Pencil,
+        Brush,
+    };
+    DrawMode m_draw_mode { DrawMode::Brush };
     bool m_use_secondary_color { false };
 };