LibGfx: Add BrightnessFilter, ContrastFilter, and OpacityFilter

These filters are based off the ones defined in:
https://drafts.fxtf.org/filter-effects-1/#supported-filter-functions

Userland/Libraries/LibGfx/Filters/BrightnessFilter.h

@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2022, MacDue <macdue@dueutil.tech>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/StringView.h>
+#include <LibGfx/Filters/ColorFilter.h>
+
+namespace Gfx {
+
+class BrightnessFilter : public ColorFilter {
+public:
+    using ColorFilter::ColorFilter;
+    virtual ~BrightnessFilter() = default;
+
+    virtual StringView class_name() const override { return "BrightnessFilter"sv; }
+
+    virtual bool amount_handled_in_filter() const override
+    {
+        return true;
+    }
+
+protected:
+    Color convert_color(Color original) override
+    {
+        auto convert_channel = [&](u8 channel) {
+            return static_cast<u8>(clamp(round_to<int>(channel * m_amount), 0, 255));
+        };
+        return Gfx::Color {
+            convert_channel(original.red()),
+            convert_channel(original.green()),
+            convert_channel(original.blue()),
+            original.alpha()
+        };
+    };
+};
+
+}

Userland/Libraries/LibGfx/Filters/ContrastFilter.h

@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2022, MacDue <macdue@dueutil.tech>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/StringView.h>
+#include <LibGfx/Filters/ColorFilter.h>
+
+namespace Gfx {
+
+class ContrastFilter : public ColorFilter {
+public:
+    using ColorFilter::ColorFilter;
+    virtual ~ContrastFilter() = default;
+
+    virtual StringView class_name() const override { return "ContrastFilter"sv; }
+
+    virtual bool amount_handled_in_filter() const override
+    {
+        return true;
+    }
+
+protected:
+    Color convert_color(Color original) override
+    {
+        auto convert_channel = [&](u8 channel) {
+            return static_cast<u8>(clamp(round_to<int>(channel * m_amount + (-128 * m_amount) + 128), 0, 255));
+        };
+        return Gfx::Color {
+            convert_channel(original.red()),
+            convert_channel(original.green()),
+            convert_channel(original.blue()),
+            original.alpha()
+        };
+    };
+};
+
+}

Userland/Libraries/LibGfx/Filters/OpacityFilter.h

@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) 2022, MacDue <macdue@dueutil.tech>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/StringView.h>
+#include <LibGfx/Filters/ColorFilter.h>
+
+namespace Gfx {
+
+class OpacityFilter : public ColorFilter {
+public:
+    using ColorFilter::ColorFilter;
+    virtual ~OpacityFilter() = default;
+
+    virtual StringView class_name() const override { return "OpacityFilter"sv; }
+
+    virtual bool amount_handled_in_filter() const override
+    {
+        return true;
+    }
+
+protected:
+    Color convert_color(Color original) override
+    {
+        return original.with_alpha(m_amount * 255);
+    };
+};
+
+}