Add the -servo-overflow-clip-box property.

components/layout/display_list_builder.rs

@@ -44,6 +44,7 @@ use std::default::Default;
 use std::sync::Arc;
 use std::{cmp, f32};
 use style::computed_values::filter::Filter;
+use style::computed_values::{_servo_overflow_clip_box as overflow_clip_box};
 use style::computed_values::{background_attachment, background_clip, background_origin};
 use style::computed_values::{background_repeat, background_size};
 use style::computed_values::{border_style, image_rendering, overflow_x, position};
@@ -1430,6 +1431,25 @@ impl FragmentDisplayListBuilding for Fragment {
         // Account for style-specified `clip`.
         self.adjust_clip_for_style(current_clip, stacking_relative_border_box);
 
+        let overflow_x = self.style.get_box().overflow_x;
+        let overflow_y = self.style.get_box().overflow_y.0;
+
+        if let (overflow_x::T::visible, overflow_x::T::visible) = (overflow_x, overflow_y) {
+            return
+        }
+
+        let tmp;
+        let overflow_clip_rect = match self.style.get_box()._servo_overflow_clip_box {
+            overflow_clip_box::T::padding_box => {
+                // FIXME(SimonSapin): should be the padding box, not border box.
+                stacking_relative_border_box
+            }
+            overflow_clip_box::T::content_box => {
+                tmp = self.stacking_relative_content_box(stacking_relative_border_box);
+                &tmp
+            }
+        };
+
         // Clip according to the values of `overflow-x` and `overflow-y`.
         //
         // TODO(pcwalton): Support scrolling of non-absolutely-positioned elements.
@@ -1441,8 +1461,8 @@ impl FragmentDisplayListBuilding for Fragment {
             (overflow_x::T::auto, false) |
             (overflow_x::T::scroll, false) => {
                 let mut bounds = current_clip.bounding_rect();
-                let max_x = cmp::min(bounds.max_x(), stacking_relative_border_box.max_x());
+                let max_x = cmp::min(bounds.max_x(), overflow_clip_rect.max_x());
-                bounds.origin.x = cmp::max(bounds.origin.x, stacking_relative_border_box.origin.x);
+                bounds.origin.x = cmp::max(bounds.origin.x, overflow_clip_rect.origin.x);
                 bounds.size.width = max_x - bounds.origin.x;
                 current_clip.intersect_rect(&bounds)
             }
@@ -1453,8 +1473,8 @@ impl FragmentDisplayListBuilding for Fragment {
             (overflow_x::T::auto, false) |
             (overflow_x::T::scroll, false) => {
                 let mut bounds = current_clip.bounding_rect();
-                let max_y = cmp::min(bounds.max_y(), stacking_relative_border_box.max_y());
+                let max_y = cmp::min(bounds.max_y(), overflow_clip_rect.max_y());
-                bounds.origin.y = cmp::max(bounds.origin.y, stacking_relative_border_box.origin.y);
+                bounds.origin.y = cmp::max(bounds.origin.y, overflow_clip_rect.origin.y);
                 bounds.size.height = max_y - bounds.origin.y;
                 current_clip.intersect_rect(&bounds)
             }

components/style/properties.mako.rs

@@ -854,6 +854,9 @@ pub mod longhands {
 
     // CSS 2.1, Section 11 - Visual effects
 
+    // Non-standard, see https://developer.mozilla.org/en-US/docs/Web/CSS/overflow-clip-box#Specifications
+    ${single_keyword("-servo-overflow-clip-box", "padding-box content-box", internal=True)}
+
     // FIXME(pcwalton, #2742): Implement scrolling for `scroll` and `auto`.
     <%self:single_keyword_computed name="overflow-x" values="visible hidden scroll auto">
         use values::computed::Context;
@@ -5638,6 +5641,7 @@ mod property_bit_field {
 
 % for property in LONGHANDS:
     % if property.derived_from is None:
+        #[allow(non_snake_case)]
         fn substitute_variables_${property.ident}<F, R>(
             value: &DeclaredValue<longhands::${property.ident}::SpecifiedValue>,
             custom_properties: &Option<Arc<::custom_properties::ComputedValuesMap>>,
@@ -5661,6 +5665,7 @@ mod property_bit_field {
             }
         }
 
+        #[allow(non_snake_case)]
         #[inline(never)]
         fn substitute_variables_${property.ident}_slow<F, R>(
                 css: &String,