Integrate iframes into the display list

Instead of always promoting iframes to StackingContexts, integrate them
into the display list. This prevents stacking bugs when
non-stacking-context elements should be drawn on top of iframes.

To accomplish this, we add another step to ordering layer creation,
where LayeredItems in the DisplayList are added to layers described by
the LayerInfo structures collected at the end of the DisplayList.
Unlayered items that follow these layered items are added to
synthesized layers.

Another result of this change is that iframe layers can be positioned
directly at the location of the iframe fragment, eliminating the need
for the SubpageLayerInfo struct entirely.

Iframes are the first type of content treated this way, but this change
opens up the possibility to properly order canvas and all other layered
content that does not create a stacking context.

Fixes #7566.
Fixes #7796.

components/layout/display_list_builder.rs

@@ -15,6 +15,7 @@ use azure::azure_hl::Color;
 use block::BlockFlow;
 use canvas_traits::{CanvasMsg, FromLayoutMsg};
 use context::LayoutContext;
+use euclid::num::Zero;
 use euclid::{Matrix4, Point2D, Point3D, Rect, SideOffsets2D, Size2D};
 use flex::FlexFlow;
 use flow::{self, BaseFlow, Flow, IS_ABSOLUTELY_POSITIONED};
@@ -25,8 +26,8 @@ use gfx::display_list::{BLUR_INFLATION_FACTOR, BaseDisplayItem, BorderDisplayIte
 use gfx::display_list::{BorderRadii, BoxShadowClipMode, BoxShadowDisplayItem, ClippingRegion};
 use gfx::display_list::{DisplayItem, DisplayItemMetadata, DisplayList};
 use gfx::display_list::{GradientDisplayItem};
-use gfx::display_list::{GradientStop, ImageDisplayItem, LayerInfo, LineDisplayItem};
-use gfx::display_list::{OpaqueNode, SolidColorDisplayItem};
+use gfx::display_list::{GradientStop, ImageDisplayItem, LayeredItem, LayerInfo};
+use gfx::display_list::{LineDisplayItem, OpaqueNode, SolidColorDisplayItem};
 use gfx::display_list::{StackingContext, TextDisplayItem, TextOrientation};
 use gfx::paint_task::THREAD_TINT_COLORS;
 use gfx::text::glyph::CharIndex;
@@ -35,7 +36,7 @@ use inline::{FIRST_FRAGMENT_OF_ELEMENT, InlineFlow, LAST_FRAGMENT_OF_ELEMENT};
 use ipc_channel::ipc::{self, IpcSharedMemory};
 use list_item::ListItemFlow;
 use model::{self, MaybeAuto, ToGfxMatrix};
-use msg::compositor_msg::{ScrollPolicy, SubpageLayerInfo};
+use msg::compositor_msg::ScrollPolicy;
 use net_traits::image::base::{Image, PixelFormat};
 use net_traits::image_cache_task::UsePlaceholder;
 use std::default::Default;
@@ -1098,7 +1099,6 @@ impl FragmentDisplayListBuilding for Fragment {
             }
             SpecificFragmentInfo::Generic |
             SpecificFragmentInfo::GeneratedContent(..) |
-            SpecificFragmentInfo::Iframe(..) |
             SpecificFragmentInfo::Table |
             SpecificFragmentInfo::TableCell |
             SpecificFragmentInfo::TableRow |
@@ -1112,6 +1112,27 @@ impl FragmentDisplayListBuilding for Fragment {
                                                              clip);
                 }
             }
+            SpecificFragmentInfo::Iframe(ref fragment_info) => {
+                // TODO(mrobinson): When https://github.com/servo/euclid/issues/109 is fixed this
+                // check can just become stacking_relative_content_box.is_empty().
+                if stacking_relative_content_box.size.width != Zero::zero() &&
+                   stacking_relative_content_box.size.height != Zero::zero() {
+                    let layer_id = self.layer_id();
+                    display_list.content.push_back(DisplayItem::LayeredItemClass(box LayeredItem {
+                        item: DisplayItem::NoopClass(
+                            box BaseDisplayItem::new(stacking_relative_content_box,
+                                                     DisplayItemMetadata::new(self.node,
+                                                                              &*self.style,
+                                                                              Cursor::DefaultCursor),
+                                                     (*clip).clone())),
+                        layer_id: layer_id
+                    }));
+
+                    display_list.layer_info.push_back(LayerInfo::new(layer_id,
+                                                                     ScrollPolicy::Scrollable,
+                                                                     Some(fragment_info.pipeline_id)));
+                }
+            }
             SpecificFragmentInfo::Image(ref mut image_fragment) => {
                 // Place the image into the display list.
                 if let Some(ref image) = image_fragment.image {
@@ -1284,19 +1305,8 @@ impl FragmentDisplayListBuilding for Fragment {
             filters.push(Filter::Opacity(effects.opacity))
         }
 
-        let subpage_layer_info = match self.specific {
-            SpecificFragmentInfo::Iframe(ref iframe_fragment_info) => {
-                let border_padding = self.border_padding.to_physical(self.style().writing_mode);
-                Some(SubpageLayerInfo {
-                    pipeline_id: iframe_fragment_info.pipeline_id,
-                    origin: Point2D::new(border_padding.left, border_padding.top),
-                })
-            }
-            _ => None,
-        };
-
-        let canvas_or_iframe = match self.specific {
-            SpecificFragmentInfo::Canvas(_) | SpecificFragmentInfo::Iframe(_) => true,
+        let canvas = match self.specific {
+            SpecificFragmentInfo::Canvas(_) => true,
             _ => false
         };
 
@@ -1304,11 +1314,9 @@ impl FragmentDisplayListBuilding for Fragment {
         // flag, when this is a canvas or iframe fragment, and when we are building a layer
         // tree for overflow scrolling.
         let layer_info = if mode == StackingContextCreationMode::InnerScrollWrapper {
-            Some(LayerInfo::new(self.layer_id_for_overflow_scroll(),
-                                scroll_policy,
-                                subpage_layer_info))
-        } else if self.flags.contains(HAS_LAYER) || canvas_or_iframe {
-            Some(LayerInfo::new(self.layer_id(), scroll_policy, subpage_layer_info))
+            Some(LayerInfo::new(self.layer_id_for_overflow_scroll(), scroll_policy, None))
+        } else if self.flags.contains(HAS_LAYER) || canvas {
+            Some(LayerInfo::new(self.layer_id(), scroll_policy, None))
         } else {
             None
         };

components/layout/fragment.rs

@@ -2102,11 +2102,11 @@ impl Fragment {
     }
 
     /// Returns true if this fragment unconditionally layerizes.
-    pub fn needs_layer(&self) -> bool {
+    pub fn needs_layered_stacking_context(&self) -> bool {
         // Canvas and iframes always layerize, as an special case
         // FIXME(pcwalton): Don't unconditionally form stacking contexts for each canvas.
         match self.specific {
-            SpecificFragmentInfo::Canvas(_) | SpecificFragmentInfo::Iframe(_) => true,
+            SpecificFragmentInfo::Canvas(_) => true,
             _ => false,
         }
     }
@@ -2135,7 +2135,7 @@ impl Fragment {
             transform_style::T::auto => {}
         }
 
-        if self.needs_layer() {
+        if self.needs_layered_stacking_context() {
             return true
         }
 

components/layout/inline.rs

@@ -1504,7 +1504,7 @@ impl Flow for InlineFlow {
             for fragment_index in line.range.each_index() {
                 let fragment = &mut self.fragments.fragments[fragment_index.to_usize()];
 
-                if fragment.needs_layer() && !fragment.is_positioned() {
+                if fragment.needs_layered_stacking_context() && !fragment.is_positioned() {
                     layers_needed_for_descendants = true
                 }