PixelPaint: Add invert filter

Userland/Libraries/LibGfx/Filters/InvertFilter.h

@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 2021, Musab Kılıç <musabkilic@protonmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibGfx/Filters/Filter.h>
+
+namespace Gfx {
+
+class InvertFilter : public Filter {
+public:
+    InvertFilter() { }
+    virtual ~InvertFilter() { }
+
+    virtual char const* class_name() const override { return "InvertFilter"; }
+
+    virtual void apply(Bitmap& target_bitmap, IntRect const& target_rect, Bitmap const& source_bitmap, IntRect const& source_rect) override
+    {
+        // source_rect should be describing the pixels that can be accessed
+        // to apply this filter, while target_rect should describe the area
+        // where to apply the filter on.
+        VERIFY(source_rect.size() == target_rect.size());
+        VERIFY(target_bitmap.rect().contains(target_rect));
+        VERIFY(source_bitmap.rect().contains(source_rect));
+
+        for (auto y = 0; y < source_rect.height(); ++y) {
+            ssize_t source_y = y + source_rect.y();
+            ssize_t target_y = y + target_rect.y();
+            for (auto x = 0; x < source_rect.width(); ++x) {
+                ssize_t source_x = x + source_rect.x();
+                ssize_t target_x = x + target_rect.x();
+
+                auto source_pixel = source_bitmap.get_pixel(source_x, source_y);
+                auto target_color = source_pixel.inverted();
+
+                target_bitmap.set_pixel(target_x, target_y, target_color);
+            }
+        }
+    }
+};
+
+}