2 files changed, 75 insertions, 0 deletions
diff --git a/Userland/Libraries/LibWeb/Painting/ShadowPainting.cpp b/Userland/Libraries/LibWeb/Painting/ShadowPainting.cpp
new file mode 100644
index 0000000000..8b5c93ed7e
--- /dev/null
+++ b/Userland/Libraries/LibWeb/Painting/ShadowPainting.cpp
@@ -0,0 +1,53 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2021, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibGfx/DisjointRectSet.h>
+#include <LibGfx/Filters/FastBoxBlurFilter.h>
+#include <LibGfx/Painter.h>
+#include <LibWeb/Painting/PaintContext.h>
+#include <LibWeb/Painting/ShadowPainting.h>
+
+namespace Web::Painting {
+
+void paint_box_shadow(PaintContext& context, Gfx::IntRect const& content_rect, BoxShadowData const& box_shadow_data)
+{
+    Gfx::IntRect bitmap_rect = {
+        0,
+        0,
+        content_rect.width() + 4 * box_shadow_data.blur_radius,
+        content_rect.height() + 4 * box_shadow_data.blur_radius
+    };
+
+    Gfx::IntPoint blur_rect_position = {
+        content_rect.x() - 2 * box_shadow_data.blur_radius + box_shadow_data.offset_x,
+        content_rect.y() - 2 * box_shadow_data.blur_radius + box_shadow_data.offset_y
+    };
+
+    if (bitmap_rect.is_empty())
+        return;
+
+    auto new_bitmap = Gfx::Bitmap::try_create(Gfx::BitmapFormat::BGRA8888, bitmap_rect.size());
+    if (!new_bitmap) {
+        dbgln("Unable to allocate temporary bitmap for box-shadow rendering");
+        return;
+    }
+
+    Gfx::Painter painter(*new_bitmap);
+    painter.fill_rect({ { 2 * box_shadow_data.blur_radius, 2 * box_shadow_data.blur_radius }, content_rect.size() }, box_shadow_data.color);
+
+    Gfx::FastBoxBlurFilter filter(*new_bitmap);
+    filter.apply_three_passes(box_shadow_data.blur_radius);
+
+    Gfx::DisjointRectSet rect_set;
+    rect_set.add(bitmap_rect);
+    auto shattered = rect_set.shatter({ content_rect.location() - blur_rect_position, content_rect.size() });
+
+    for (auto& rect : shattered.rects())
+        context.painter().blit(rect.location() + blur_rect_position, *new_bitmap, rect);
+}
+
+}
diff --git a/Userland/Libraries/LibWeb/Painting/ShadowPainting.h b/Userland/Libraries/LibWeb/Painting/ShadowPainting.h
new file mode 100644
index 0000000000..fd330aad92
--- /dev/null
+++ b/Userland/Libraries/LibWeb/Painting/ShadowPainting.h
@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2021, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibGfx/Forward.h>
+
+namespace Web::Painting {
+
+struct BoxShadowData {
+    int offset_x;
+    int offset_y;
+    int blur_radius;
+    Gfx::Color color;
+};
+
+void paint_box_shadow(PaintContext&, Gfx::IntRect const&, BoxShadowData const&);
+
+}