PixelPaint: Add the FastBoxBlurFilter with configurable parameters :^)

The FastBoxBlurFilter has been living in LibGfx for a while and now
it's accessible in PixelPaint. The parameters for the filter are exposed
via the new Filter Gallery.

Userland/Applications/PixelPaint/CMakeLists.txt

@@ -20,6 +20,7 @@ set(SOURCES
     Filters/BoxBlur3.cpp
     Filters/BoxBlur5.cpp
     Filters/Filter.cpp
+    Filters/FastBoxBlur.cpp
     Filters/GaussBlur3.cpp
     Filters/GaussBlur5.cpp
     Filters/Grayscale.cpp

Userland/Applications/PixelPaint/FilterModel.cpp

@@ -9,6 +9,7 @@
 #include "FilterParams.h"
 #include "Filters/BoxBlur3.h"
 #include "Filters/BoxBlur5.h"
+#include "Filters/FastBoxBlur.h"
 #include "Filters/GaussBlur3.h"
 #include "Filters/GaussBlur5.h"
 #include "Filters/Grayscale.h"
@@ -29,6 +30,7 @@ FilterModel::FilterModel(ImageEditor* editor)
     auto laplace_diagonal_filter = FilterInfo::create_filter<Filters::LaplaceDiagonal>(editor, edge_detect_category);
 
     auto blur_category = FilterInfo::create_category("Blur & Sharpen", spatial_category);
+    auto fast_box_filter = FilterInfo::create_filter<Filters::FastBoxBlur>(editor, blur_category);
     auto gaussian_blur_filter_3 = FilterInfo::create_filter<Filters::GaussBlur3>(editor, blur_category);
     auto gaussian_blur_filter_5 = FilterInfo::create_filter<Filters::GaussBlur5>(editor, blur_category);
     auto box_blur_filter_3 = FilterInfo::create_filter<Filters::BoxBlur3>(editor, blur_category);

Userland/Applications/PixelPaint/Filters/FastBoxBlur.cpp

@@ -0,0 +1,74 @@
+/*
+ * Copyright (c) 2022, Tobias Christiansen <tobyase@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "FastBoxBlur.h"
+#include "../FilterParams.h"
+#include <LibGUI/Label.h>
+#include <LibGUI/ValueSlider.h>
+#include <LibGfx/Filters/FastBoxBlurFilter.h>
+
+namespace PixelPaint::Filters {
+
+void FastBoxBlur::apply() const
+{
+    if (!m_editor)
+        return;
+    if (auto* layer = m_editor->active_layer()) {
+        Gfx::FastBoxBlurFilter filter(layer->bitmap());
+
+        if (m_approximate_gauss)
+            filter.apply_three_passes(m_radius);
+        else
+            filter.apply_single_pass(m_radius);
+
+        layer->did_modify_bitmap(layer->rect());
+        m_editor->did_complete_action();
+    }
+}
+
+RefPtr<GUI::Widget> FastBoxBlur::get_settings_widget()
+{
+    if (!m_settings_widget) {
+        m_settings_widget = GUI::Widget::construct();
+        m_settings_widget->set_layout<GUI::VerticalBoxLayout>();
+
+        auto& name_label = m_settings_widget->add<GUI::Label>("Fast Box Blur Filter");
+        name_label.set_font_weight(Gfx::FontWeight::Bold);
+        name_label.set_text_alignment(Gfx::TextAlignment::CenterLeft);
+        name_label.set_fixed_height(20);
+
+        auto& radius_container = m_settings_widget->add<GUI::Widget>();
+        radius_container.set_fixed_height(20);
+        radius_container.set_layout<GUI::HorizontalBoxLayout>();
+        radius_container.layout()->set_margins({ 4, 0, 4, 0 });
+
+        auto& radius_label = radius_container.add<GUI::Label>("Radius:");
+        radius_label.set_text_alignment(Gfx::TextAlignment::CenterLeft);
+        radius_label.set_fixed_size(50, 20);
+
+        auto& radius_slider = radius_container.add<GUI::ValueSlider>(Orientation::Horizontal, "px");
+        radius_slider.set_range(0, 25);
+        radius_slider.set_value(m_radius);
+        radius_slider.on_change = [&](int value) {
+            m_radius = value;
+        };
+
+        auto& gaussian_container = m_settings_widget->add<GUI::Widget>();
+        gaussian_container.set_fixed_height(20);
+        gaussian_container.set_layout<GUI::HorizontalBoxLayout>();
+        gaussian_container.layout()->set_margins({ 4, 0, 4, 0 });
+
+        auto& gaussian_checkbox = gaussian_container.add<GUI::CheckBox>("Approximate Gaussian Blur");
+        gaussian_checkbox.set_checked(m_approximate_gauss);
+        gaussian_checkbox.set_tooltip("A real gaussian blur can be approximated by running the box blur multiple times with different weights.");
+        gaussian_checkbox.on_checked = [this](bool checked) {
+            m_approximate_gauss = checked;
+        };
+    }
+
+    return m_settings_widget;
+}
+}

Userland/Applications/PixelPaint/Filters/FastBoxBlur.h

@@ -0,0 +1,28 @@
+/*
+ * Copyright (c) 2022, Tobias Christiansen <tobyase@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include "Filter.h"
+
+namespace PixelPaint::Filters {
+
+class FastBoxBlur final : public Filter {
+public:
+    virtual void apply() const override;
+    virtual RefPtr<GUI::Widget> get_settings_widget() override;
+
+    virtual StringView filter_name() override { return "Fast Box Blur (& Gauss)"sv; }
+
+    FastBoxBlur(ImageEditor* editor)
+        : Filter(editor) {};
+
+private:
+    size_t m_radius { 5 };
+    bool m_approximate_gauss { false };
+};
+
+}