Unify background placement code

Merges the implementations for background-image placement
from gradients and images. Add missing parts and fix bugs.

Now supported are the CSS properties:

* background-attachment (except for local value)
* background-clip
* background-origin
* background-position-x/y
* background-repeat
* background-size

It should be noted that backgrounds are not clipped to
rounded border corners.

components/gfx/display_list/mod.rs

@@ -729,6 +729,7 @@ pub struct GradientDisplayItem {
     ///
     /// Without tiles, the tile will be the same size as the background.
     pub tile: Size2D<Au>,
+    pub tile_spacing: Size2D<Au>,
 }
 
 /// Paints a radial gradient.
@@ -763,6 +764,7 @@ pub struct RadialGradientDisplayItem {
     ///
     /// Without tiles, the tile will be the same size as the background.
     pub tile: Size2D<Au>,
+    pub tile_spacing: Size2D<Au>,
 }
 
 /// A normal border, supporting CSS border styles.

components/layout/fragment.rs

@@ -421,77 +421,6 @@ impl ImageFragmentInfo {
             metadata: metadata,
         }
     }
-
-    pub fn tile_image_round(position: &mut Au,
-                            size: &mut Au,
-                            absolute_anchor_origin: Au,
-                            image_size: &mut Au) {
-        if *size == Au(0) || *image_size == Au(0) {
-            *position = Au(0);
-            *size =Au(0);
-            return;
-        }
-
-        let number_of_tiles = (size.to_f32_px() / image_size.to_f32_px()).round().max(1.0);
-        *image_size = *size / (number_of_tiles as i32);
-        ImageFragmentInfo::tile_image(position, size, absolute_anchor_origin, *image_size);
-    }
-
-    pub fn tile_image_spaced(position: &mut Au,
-                             size: &mut Au,
-                             tile_spacing: &mut Au,
-                             absolute_anchor_origin: Au,
-                             image_size: Au) {
-        if *size == Au(0) || image_size == Au(0) {
-            *position = Au(0);
-            *size = Au(0);
-            *tile_spacing = Au(0);
-            return;
-        }
-
-        // Per the spec, if the space available is not enough for two images, just tile as
-        // normal but only display a single tile.
-        if image_size * 2 >= *size {
-            ImageFragmentInfo::tile_image(position,
-                                          size,
-                                          absolute_anchor_origin,
-                                          image_size);
-            *tile_spacing = Au(0);
-            *size = image_size;
-            return;
-        }
-
-        // Take the box size, remove room for two tiles on the edges, and then calculate how many
-        // other tiles fit in between them.
-        let size_remaining = *size - (image_size * 2);
-        let num_middle_tiles = (size_remaining.to_f32_px() / image_size.to_f32_px()).floor() as i32;
-
-        // Allocate the remaining space as padding between tiles. background-position is ignored
-        // as per the spec, so the position is just the box origin. We are also ignoring
-        // background-attachment here, which seems unspecced when combined with
-        // background-repeat: space.
-        let space_for_middle_tiles = image_size * num_middle_tiles;
-        *tile_spacing = (size_remaining - space_for_middle_tiles) / (num_middle_tiles + 1);
-    }
-
-    /// Tile an image
-    pub fn tile_image(position: &mut Au,
-                      size: &mut Au,
-                      absolute_anchor_origin: Au,
-                      image_size: Au) {
-        // Avoid division by zero below!
-        if image_size == Au(0) {
-            return
-        }
-
-        let delta_pixels = absolute_anchor_origin - *position;
-        let image_size_px = image_size.to_f32_px();
-        let tile_count = ((delta_pixels.to_f32_px() + image_size_px - 1.0) / image_size_px).floor();
-        let offset = image_size * (tile_count as i32);
-        let new_position = absolute_anchor_origin - offset;
-        *size = *position - new_position + *size;
-        *position = new_position;
-    }
 }
 
 /// A fragment that represents an inline frame (iframe). This stores the frame ID so that the

components/layout/webrender_helpers.rs

@@ -442,7 +442,7 @@ impl WebRenderDisplayItemConverter for DisplayItem {
                 builder.push_gradient(&self.prim_info(),
                                       gradient,
                                       item.tile.to_sizef(),
-                                      webrender_api::LayoutSize::zero());
+                                      item.tile_spacing.to_sizef());
             }
             DisplayItem::RadialGradient(ref item) => {
                 let center = item.gradient.center.to_pointf();
@@ -459,7 +459,7 @@ impl WebRenderDisplayItemConverter for DisplayItem {
                 builder.push_radial_gradient(&self.prim_info(),
                                              gradient,
                                              item.tile.to_sizef(),
-                                             webrender_api::LayoutSize::zero());
+                                             item.tile_spacing.to_sizef());
             }
             DisplayItem::Line(ref item) => {
                 builder.push_line(&self.prim_info(),