1 files changed, 78 insertions, 0 deletions
diff --git a/components/layout/incremental.rs b/components/layout/incremental.rs
new file mode 100644
index 00000000000..d04c068b6aa
--- /dev/null
+++ b/components/layout/incremental.rs
@@ -0,0 +1,78 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use style::ComputedValues;
+
+bitflags! {
+    #[doc = "Individual layout actions that may be necessary after restyling."]
+    flags RestyleDamage: int {
+        #[doc = "Repaint the node itself."]
+        #[doc = "Currently unused; need to decide how this propagates."]
+        static Repaint = 0x01,
+
+        #[doc = "Recompute intrinsic inline_sizes (minimum and preferred)."]
+        #[doc = "Propagates down the flow tree because the computation is"]
+        #[doc = "bottom-up."]
+        static BubbleISizes = 0x02,
+
+        #[doc = "Recompute actual inline_sizes and block_sizes."]
+        #[doc = "Propagates up the flow tree because the computation is"]
+        #[doc = "top-down."]
+        static Reflow = 0x04
+    }
+}
+
+impl RestyleDamage {
+    /// Elements of self which should also get set on any ancestor flow.
+    pub fn propagate_up(self) -> RestyleDamage {
+        self & Reflow
+    }
+
+    /// Elements of self which should also get set on any child flows.
+    pub fn propagate_down(self) -> RestyleDamage {
+        self & BubbleISizes
+    }
+}
+
+// NB: We need the braces inside the RHS due to Rust #8012.  This particular
+// version of this macro might be safe anyway, but we want to avoid silent
+// breakage on modifications.
+macro_rules! add_if_not_equal(
+    ($old:ident, $new:ident, $damage:ident,
+     [ $($effect:ident),* ], [ $($style_struct_getter:ident.$name:ident),* ]) => ({
+        if $( ($old.$style_struct_getter().$name != $new.$style_struct_getter().$name) )||* {
+            $damage.insert($($effect)|*);
+        }
+    })
+)
+
+pub fn compute_damage(old: &ComputedValues, new: &ComputedValues) -> RestyleDamage {
+    let mut damage = RestyleDamage::empty();
+
+    // This checks every CSS property, as enumerated in
+    // impl<'self> CssComputedStyle<'self>
+    // in src/support/netsurfcss/rust-netsurfcss/netsurfcss.rc.
+
+    // FIXME: We can short-circuit more of this.
+
+    add_if_not_equal!(old, new, damage, [ Repaint ],
+        [ get_color.color, get_background.background_color,
+          get_border.border_top_color, get_border.border_right_color,
+          get_border.border_bottom_color, get_border.border_left_color ]);
+
+    add_if_not_equal!(old, new, damage, [ Repaint, BubbleISizes, Reflow ],
+        [ get_border.border_top_width, get_border.border_right_width,
+          get_border.border_bottom_width, get_border.border_left_width,
+          get_margin.margin_top, get_margin.margin_right,
+          get_margin.margin_bottom, get_margin.margin_left,
+          get_padding.padding_top, get_padding.padding_right,
+          get_padding.padding_bottom, get_padding.padding_left,
+          get_box.position, get_box.width, get_box.height, get_box.float, get_box.display,
+          get_font.font_family, get_font.font_size, get_font.font_style, get_font.font_weight,
+          get_inheritedtext.text_align, get_text.text_decoration, get_inheritedbox.line_height ]);
+
+    // FIXME: test somehow that we checked every CSS property
+
+    damage
+}