Implement 'background-origin' property in CSS3 Background

This property determines the background positioning area, that is the position of
the origin of an image specified using the 'background-image' CSS property.

'background-origin' is ignored when background-attachment is fixed.

Spec: http://dev.w3.org/csswg/css-backgrounds-3/#background-origin

Fixes #6045.

components/layout/display_list_builder.rs

@@ -43,7 +43,7 @@ use std::sync::Arc;
 use std::sync::mpsc::channel;
 use style::computed_values::filter::Filter;
 use style::computed_values::transform::ComputedMatrix;
-use style::computed_values::{background_attachment, background_repeat, background_size};
+use style::computed_values::{background_attachment, background_origin, background_repeat, background_size};
 use style::computed_values::{border_style, image_rendering, overflow_x, position, visibility};
 use style::properties::ComputedValues;
 use style::properties::style_structs::Border;
@@ -419,12 +419,32 @@ impl FragmentDisplayListBuilding for Fragment {
             // TODO: Check the bounds to see if a clip item is actually required.
             let clip = clip.clone().intersect_rect(&bounds);
 
+            // Background image should be positioned on the padding box basis.
+            let border = style.logical_border_width().to_physical(style.writing_mode);
+
+            // Use 'background-origin' to get the origin value.
+            let (mut origin_x, mut origin_y) = match background.background_origin {
+                background_origin::T::padding_box => {
+                    (Au(0), Au(0))
+                }
+                background_origin::T::border_box => {
+                    (-border.left, -border.top)
+                }
+                background_origin::T::content_box => {
+                    let border_padding = (self.border_padding).to_physical(self.style.writing_mode);
+                    (border_padding.left - border.left, border_padding.top - border.top)
+                }
+            };
+
             // Use `background-attachment` to get the initial virtual origin
             let (virtual_origin_x, virtual_origin_y) = match background.background_attachment {
                 background_attachment::T::scroll => {
                     (absolute_bounds.origin.x, absolute_bounds.origin.y)
                 }
                 background_attachment::T::fixed => {
+                    // If the ‘background-attachment’ value for this image is ‘fixed’, then 'background-origin' has no effect.
+                    origin_x = Au(0);
+                    origin_y = Au(0);
                     (Au(0), Au(0))
                 }
             };
@@ -435,11 +455,8 @@ impl FragmentDisplayListBuilding for Fragment {
             let vertical_position = model::specified(background.background_position.vertical,
                                                      bounds.size.height - image_size.height);
 
-            // Background image should be positioned on the padding box basis.
-            let border = style.logical_border_width().to_physical(style.writing_mode);
-
-            let abs_x = border.left + virtual_origin_x + horizontal_position;
-            let abs_y = border.top + virtual_origin_y + vertical_position;
+            let abs_x = border.left + virtual_origin_x + horizontal_position + origin_x;
+            let abs_y = border.top + virtual_origin_y + vertical_position + origin_y;
 
             // Adjust origin and size based on background-repeat
             match background.background_repeat {

components/script/dom/webidls/CSSStyleDeclaration.webidl

@@ -39,6 +39,7 @@ partial interface CSSStyleDeclaration {
   [TreatNullAs=EmptyString] attribute DOMString backgroundImage;
   [TreatNullAs=EmptyString] attribute DOMString backgroundAttachment;
   [TreatNullAs=EmptyString] attribute DOMString backgroundSize;
+  [TreatNullAs=EmptyString] attribute DOMString backgroundOrigin;
 
   [TreatNullAs=EmptyString] attribute DOMString border;
   [TreatNullAs=EmptyString] attribute DOMString borderColor;

components/style/properties.mako.rs

@@ -1295,6 +1295,8 @@ pub mod longhands {
 
     ${single_keyword("background-attachment", "scroll fixed")}
 
+    ${single_keyword("background-origin", "padding-box border-box content-box")}
+
     <%self:longhand name="background-size">
         use cssparser::{ToCss, Token};
         use std::ascii::AsciiExt;
@@ -4244,9 +4246,10 @@ pub mod shorthands {
 
     // TODO: other background-* properties
     <%self:shorthand name="background"
-                     sub_properties="background-color background-position background-repeat background-attachment background-image background-size">
+                     sub_properties="background-color background-position background-repeat background-attachment
+                                     background-image background-size background-origin">
         use properties::longhands::{background_color, background_position, background_repeat};
-        use properties::longhands::{background_attachment, background_image, background_size};
+        use properties::longhands::{background_attachment, background_image, background_size, background_origin};
 
         let mut color = None;
         let mut image = None;
@@ -4255,6 +4258,7 @@ pub mod shorthands {
         let mut size = None;
         let mut attachment = None;
         let mut any = false;
+        let mut origin = None;
 
         loop {
             if position.is_none() {
@@ -4299,6 +4303,13 @@ pub mod shorthands {
                     continue
                 }
             }
+            if origin.is_none() {
+                if let Ok(value) = input.try(|input| background_origin::parse(context, input)) {
+                    origin = Some(value);
+                    any = true;
+                    continue
+                }
+            }
             break
         }
 
@@ -4310,6 +4321,7 @@ pub mod shorthands {
                 background_repeat: repeat,
                 background_attachment: attachment,
                 background_size: size,
+                background_origin: origin,
             })
         } else {
             Err(())

tests/ref/background_origin_a.html

@@ -0,0 +1,40 @@
+<!DOCTYPE html>
+<html>
+<head>
+<style>
+#foo1 {
+    background: url(400x400_green.png);
+    background-origin: padding-box;
+    background-repeat: no-repeat;
+    width: 400px;
+    height: 400px;
+    padding: 20px;
+    border: 20px dotted red;
+}
+#foo2 {
+    background: url(400x400_green.png);
+    background-origin: border-box;
+    background-repeat: no-repeat;
+    width: 400px;
+    height: 400px;
+    padding: 20px;
+    border: 20px dotted red;
+}
+#foo3 {
+    background: url(400x400_green.png);
+    background-origin: content-box;
+    background-repeat: no-repeat;
+    width: 400px;
+    height: 400px;
+    padding: 20px;
+    border: 20px dotted red;
+}
+</style>
+</head>
+<body>
+<div id=foo1></div>
+<div id=foo2></div>
+<div id=foo3></div>
+</body>
+</html>
+

tests/ref/background_origin_ref.html

@@ -0,0 +1,39 @@
+<!DOCTYPE html>
+<html>
+<head>
+<style>
+#foo1 {
+    background: url(400x400_green.png);
+    background-repeat: no-repeat;
+    width: 400px;
+    height: 400px;
+    padding: 20px;
+    border: 20px dotted red;
+}
+#foo2 {
+    background: url(400x400_green.png);
+    background-position: -20px -20px;
+    background-repeat: no-repeat;
+    width: 400px;
+    height: 400px;
+    padding: 20px;
+    border: 20px dotted red;
+}
+#foo3 {
+    background: url(400x400_green.png);
+    background-position: 20px 20px;
+    background-repeat: no-repeat;
+    width: 400px;
+    height: 400px;
+    padding: 20px;
+    border: 20px dotted red;
+}
+</style>
+</head>
+<body>
+<div id=foo1></div>
+<div id=foo2></div>
+<div id=foo3></div>
+</body>
+</html>
+

tests/ref/basic.list

@@ -25,6 +25,7 @@ flaky_cpu == append_style_a.html append_style_b.html
 == background_external_stylesheet.html background_ref.html
 == background_image_position_a.html background_image_position_ref.html
 == background_none_a.html background_none_b.html
+== background_origin_a.html background_origin_ref.html
 == background_position_a.html background_position_b.html
 == background_position_keyword.html background_position_b.html
 == background_position_percent.html background_position_b.html

tests/unit/style/stylesheets.rs

@@ -116,6 +116,7 @@ fn test_parse_stylesheet() {
                 ],
                 declarations: PropertyDeclarationBlock {
                     normal: Arc::new(vec![
+                        PropertyDeclaration::BackgroundOrigin(DeclaredValue::Initial),
                         PropertyDeclaration::BackgroundSize(DeclaredValue::Initial),
                         PropertyDeclaration::BackgroundImage(DeclaredValue::Initial),
                         PropertyDeclaration::BackgroundAttachment(DeclaredValue::Initial),