auto merge of #1440 : ibnc/servo/position_fixed, r=larsbergstrom

Actually removing from the normal flow will come later. 

There are some fixes for the positioned box offsets, like actually parsing percentages and naming consistency. 

6 files changed, 225 insertions, 28 deletions

diff --git a/src/components/main/layout/block.rs b/src/components/main/layout/block.rs
index 0aa4cf42d56..a31b1a8fd03 100644
--- a/src/components/main/layout/block.rs
+++ b/src/components/main/layout/block.rs
@@ -55,9 +55,12 @@ pub struct BlockFlow {
     /// The associated box.
     box_: Option<Box>,
 
+    //TODO: is_fixed and is_root should be bit fields to conserve memory.
     /// Whether this block flow is the root flow.
     is_root: bool,
 
+    is_fixed: bool,
+
     /// Additional floating flow members.
     float: Option<~FloatedBlockInfo>
 }
@@ -68,15 +71,17 @@ impl BlockFlow {
             base: base,
             box_: None,
             is_root: false,
+            is_fixed: false,
             float: None
         }
     }
 
-    pub fn from_box(base: BaseFlow, box_: Box) -> BlockFlow {
+    pub fn from_box(base: BaseFlow, box_: Box, is_fixed: bool) -> BlockFlow {
         BlockFlow {
             base: base,
             box_: Some(box_),
             is_root: false,
+            is_fixed: is_fixed,
             float: None
         }
     }
@@ -86,6 +91,7 @@ impl BlockFlow {
             base: base,
             box_: Some(box_),
             is_root: false,
+            is_fixed: false,
             float: Some(~FloatedBlockInfo::new(float_type))
         }
     }
@@ -95,6 +101,7 @@ impl BlockFlow {
             base: base,
             box_: None,
             is_root: true,
+            is_fixed: false,
             float: None
         }
     }
@@ -104,6 +111,7 @@ impl BlockFlow {
             base: base,
             box_: None,
             is_root: false,
+            is_fixed: false,
             float: Some(~FloatedBlockInfo::new(float_type))
         }
     }
@@ -353,11 +361,26 @@ impl BlockFlow {
             margin.top = margin_top;
             margin.bottom = margin_bottom;
 
-            position.origin.y = clearance + margin.top;
-
             noncontent_height = box_.padding.get().top + box_.padding.get().bottom +
                 box_.border.get().top + box_.border.get().bottom;
-            position.size.height = height + noncontent_height;
+
+            let (y, h) = box_.get_y_coord_and_new_height_if_fixed(ctx.screen_size.size.height,
+                                                                 height, clearance + margin.top, self.is_fixed);
+            position.origin.y = y;
+            height = h;
+
+            if self.is_fixed { 
+                for kid in self.base.child_iter() {
+                    let child_node = flow::mut_base(*kid);
+                    child_node.position.origin.y = position.origin.y + top_offset;
+                }
+            }
+
+            position.size.height = if self.is_fixed {
+                height
+            } else {
+                height + noncontent_height
+            };
 
             noncontent_height = noncontent_height + clearance + margin.top + margin.bottom;
 
@@ -365,7 +388,11 @@ impl BlockFlow {
             box_.margin.set(margin);
         }
 
-        self.base.position.size.height = height + noncontent_height;
+        self.base.position.size.height = if self.is_fixed {
+            height
+        } else {
+            height + noncontent_height
+        };
 
         if inorder {
             let extra_height = height - (cur_y - top_offset) + bottom_offset;
@@ -482,9 +509,9 @@ impl BlockFlow {
         for box_ in self.box_.iter() {
             box_.build_display_list(builder, dirty, self.base.abs_position, (&*self) as &Flow, list)
         }
-
         // TODO: handle any out-of-flow elements
         let this_position = self.base.abs_position;
+
         for child in self.base.child_iter() {
             let child_base = flow::mut_base(*child);
             child_base.abs_position = this_position + child_base.position.origin;
@@ -641,12 +668,19 @@ impl Flow for BlockFlow {
                                               margin_bottom,
                                               margin_left));
 
-            x_offset = box_.offset();
-            remaining_width = width;
+            let (x, w) = box_.get_x_coord_and_new_width_if_fixed(ctx.screen_size.size.width, 
+                                                            ctx.screen_size.size.height, width, box_.offset(), self.is_fixed);
+            x_offset = x;
+            remaining_width = w;
 
             // The associated box is the border box of this flow.
             let mut position_ref = box_.position.borrow_mut();
-            position_ref.get().origin.x = box_.margin.get().left;
+            if self.is_fixed {
+                position_ref.get().origin.x = x_offset + box_.margin.get().left;
+                x_offset = x_offset + box_.padding.get().left;
+            } else {
+                position_ref.get().origin.x = box_.margin.get().left;
+            }
             let padding_and_borders = box_.padding.get().left + box_.padding.get().right +
                 box_.border.get().left + box_.border.get().right;
             position_ref.get().size.width = remaining_width + padding_and_borders;
diff --git a/src/components/main/layout/box_.rs b/src/components/main/layout/box_.rs
index bd7ba5bd000..39cb0004df1 100644
--- a/src/components/main/layout/box_.rs
+++ b/src/components/main/layout/box_.rs
@@ -37,7 +37,7 @@ use layout::display_list_builder::{DisplayListBuilder, ExtraDisplayListData, ToG
 use layout::float_context::{ClearType, ClearLeft, ClearRight, ClearBoth};
 use layout::flow::Flow;
 use layout::flow;
-use layout::model::{MaybeAuto, specified};
+use layout::model::{MaybeAuto, Auto, specified};
 use layout::util::OpaqueNode;
 use layout::wrapper::LayoutNode;
 
@@ -306,6 +306,71 @@ impl Box {
         }
     }
 
+    //TODO(ibnc) take into account padding.
+    pub fn get_y_coord_and_new_height_if_fixed(&self, 
+                                               screen_height: Au,
+                                               mut height: Au,
+                                               mut y: Au,
+                                               is_fixed: bool)
+                                               -> (Au, Au) {
+        if is_fixed { 
+            let position_offsets = self.position_offsets.get();
+            match (position_offsets.top, position_offsets.bottom) {
+                (Au(0), Au(0)) => {}
+                (Au(0), _) => {
+                    y = screen_height - position_offsets.bottom - height;
+                }
+                (_, Au(0)) => {
+                    y = position_offsets.top;
+                }
+                (_, _) => {
+                    y = position_offsets.top;
+                    match MaybeAuto::from_style(self.style().Box.height, Au(0)) {
+                        Auto => {
+                            height = screen_height - position_offsets.top - position_offsets.bottom;
+                        }
+                        _ => {}
+                    }
+                }
+            }
+        }
+        return (y, height);
+    }
+
+    //TODO(ibnc) removing padding when width needs to be stretched.
+    pub fn get_x_coord_and_new_width_if_fixed(&self,
+                                              screen_width: Au,
+                                              screen_height: Au,
+                                              mut width: Au,
+                                              mut x: Au,
+                                              is_fixed: bool)
+                                              -> (Au, Au) {
+        if is_fixed {
+            self.compute_positioned_offsets(self.style(), screen_width, screen_height);
+            let position_offsets = self.position_offsets.get();
+
+            match (position_offsets.left, position_offsets.right) {
+                (Au(0), Au(0)) => {}
+                (_, Au(0)) => {
+                   x = position_offsets.left;
+                }
+                (Au(0), _) => {
+                    x = screen_width - position_offsets.right - width;
+                }
+                (_, _) => {
+                    x = position_offsets.left;
+                    match MaybeAuto::from_style(self.style().Box.width, Au(0)) {
+                        Auto => {
+                            width = screen_width - position_offsets.left - position_offsets.right;
+                        }
+                        _ => {}
+                    }
+                }
+            }
+        }
+        return (x, width);
+    }
+
     /// Transforms this box into another box of the given type, with the given size, preserving all
     /// the other data.
     pub fn transform(&self, size: Size2D<Au>, specific: SpecificBoxInfo) -> Box {
@@ -375,12 +440,16 @@ impl Box {
                                                  style.Border.border_left_style)))
     }
 
-    pub fn compute_positioned_offset(&self, style: &ComputedValues) {
+    pub fn compute_positioned_offsets(&self, style: &ComputedValues, containing_width: Au, containing_height: Au) {
         self.position_offsets.set(SideOffsets2D::new(
-                MaybeAuto::from_style(style.PositionOffsets.top, Au::new(0)).specified_or_zero(),
-                MaybeAuto::from_style(style.PositionOffsets.right, Au::new(0)).specified_or_zero(),
-                MaybeAuto::from_style(style.PositionOffsets.bottom, Au::new(0)).specified_or_zero(),
-                MaybeAuto::from_style(style.PositionOffsets.left, Au::new(0)).specified_or_zero()));
+                MaybeAuto::from_style(style.PositionOffsets.top, containing_height)
+                .specified_or_zero(),
+                MaybeAuto::from_style(style.PositionOffsets.right, containing_width)
+                .specified_or_zero(),
+                MaybeAuto::from_style(style.PositionOffsets.bottom, containing_height)
+                .specified_or_zero(),
+                MaybeAuto::from_style(style.PositionOffsets.left, containing_width)
+                .specified_or_zero()));
     }
 
     /// Populates the box model padding parameters from the given computed style.
diff --git a/src/components/main/layout/construct.rs b/src/components/main/layout/construct.rs
index 017dffecd0b..ee06fa20af7 100644
--- a/src/components/main/layout/construct.rs
+++ b/src/components/main/layout/construct.rs
@@ -35,7 +35,7 @@ use layout::wrapper::{LayoutNode, PostorderNodeMutTraversal};
 use script::dom::element::{HTMLIframeElementTypeId, HTMLImageElementTypeId};
 use script::dom::node::{CommentNodeTypeId, DoctypeNodeTypeId, DocumentFragmentNodeTypeId};
 use script::dom::node::{DocumentNodeTypeId, ElementNodeTypeId, TextNodeTypeId};
-use style::computed_values::{display, float};
+use style::computed_values::{display, position, float};
 
 use std::cell::RefCell;
 use std::util;
@@ -344,10 +344,10 @@ impl<'fc> FlowConstructor<'fc> {
     /// Builds a flow for a node with `display: block`. This yields a `BlockFlow` with possibly
     /// other `BlockFlow`s or `InlineFlow`s underneath it, depending on whether {ib} splits needed
     /// to happen.
-    fn build_flow_for_block(&mut self, node: LayoutNode) -> ~Flow {
+    fn build_flow_for_block(&mut self, node: LayoutNode, is_fixed: bool) -> ~Flow {
         let base = BaseFlow::new(self.next_flow_id(), node);
         let box_ = self.build_box_for_node(node);
-        let mut flow = ~BlockFlow::from_box(base, box_) as ~Flow;
+        let mut flow = ~BlockFlow::from_box(base, box_, is_fixed) as ~Flow;
         self.build_children_of_block_flow(&mut flow, node);
         flow
     }
@@ -363,6 +363,7 @@ impl<'fc> FlowConstructor<'fc> {
         flow
     }
 
+
     /// Concatenates the boxes of kids, adding in our own borders/padding/margins if necessary.
     /// Returns the `InlineBoxesConstructionResult`, if any. There will be no
     /// `InlineBoxesConstructionResult` if this node consisted entirely of ignorable whitespace.
@@ -504,47 +505,53 @@ impl<'a> PostorderNodeMutTraversal for FlowConstructor<'a> {
     #[inline(always)]
     fn process(&mut self, node: LayoutNode) -> bool {
         // Get the `display` property for this node, and determine whether this node is floated.
-        let (display, float) = match node.type_id() {
+        let (display, float, position) = match node.type_id() {
             ElementNodeTypeId(_) => {
                 let style = node.style().get();
-                (style.Box.display, style.Box.float)
+                (style.Box.display, style.Box.float, style.Box.position)
             }
-            TextNodeTypeId => (display::inline, float::none),
+            TextNodeTypeId => (display::inline, float::none, position::static_),
             CommentNodeTypeId |
             DoctypeNodeTypeId |
             DocumentFragmentNodeTypeId |
-            DocumentNodeTypeId(_) => (display::none, float::none),
+            DocumentNodeTypeId(_) => (display::none, float::none, position::static_),
         };
 
         debug!("building flow for node: {:?} {:?}", display, float);
 
         // Switch on display and floatedness.
-        match (display, float) {
+        match (display, float, position) {
             // `display: none` contributes no flow construction result. Nuke the flow construction
             // results of children.
-            (display::none, _) => {
+            (display::none, _, _) => {
                 for child in node.children() {
                     child.set_flow_construction_result(NoConstructionResult)
                 }
             }
 
             // Inline items contribute inline box construction results.
-            (display::inline, float::none) => {
+            (display::inline, float::none, _) => {
                 let construction_result = self.build_boxes_for_inline(node);
                 node.set_flow_construction_result(construction_result)
+
             }
 
             // Block flows that are not floated contribute block flow construction results.
             //
             // TODO(pcwalton): Make this only trigger for blocks and handle the other `display`
             // properties separately.
-            (_, float::none) => {
-                let flow = self.build_flow_for_block(node);
+
+            (_, _, position::fixed) => {
+                let flow = self.build_flow_for_block(node, true);
+                node.set_flow_construction_result(FlowConstructionResult(flow))
+            }
+            (_, float::none, _) => {
+                let flow = self.build_flow_for_block(node, false);
                 node.set_flow_construction_result(FlowConstructionResult(flow))
             }
 
             // Floated flows contribute float flow construction results.
-            (_, float_value) => {
+            (_, float_value, _) => {
                 let float_type = FloatType::from_property(float_value);
                 let flow = self.build_flow_for_floated_block(node, float_type);
                 node.set_flow_construction_result(FlowConstructionResult(flow))
diff --git a/src/test/ref/basic.list b/src/test/ref/basic.list
index 732f6b1e14a..3ce729e74dc 100644
--- a/src/test/ref/basic.list
+++ b/src/test/ref/basic.list
@@ -21,3 +21,4 @@
 == inline_text_align_a.html inline_text_align_b.html
 == font_size_em.html font_size_em_ref.html
 == font_size_percentage.html font_size_em_ref.html
+== position_fixed_a.html position_fixed_b.html
diff --git a/src/test/ref/position_fixed_a.html b/src/test/ref/position_fixed_a.html
new file mode 100644
index 00000000000..1fe3fc1ec45
--- /dev/null
+++ b/src/test/ref/position_fixed_a.html
@@ -0,0 +1,43 @@
+<html>
+  <head>
+    <style>
+    .container {
+      display: block;
+      background: blue;
+    }
+    .fixed_block {
+      background: green;
+      position: fixed;
+    }
+    .positioned_fixed_block {
+      background: yellow;
+      position: fixed;
+      top: 50%;
+      right: 25px;
+    }
+    .sized_fixed_block {
+      background: red;
+      position: fixed;
+      height: 50px;
+      width: 50px;
+      left: 5px;
+      right: 10px;
+      top: 100px;
+      bottom: 30px;
+    }
+    .stretched_fixed_block {
+      position: fixed;
+      background: black;
+      top: 100px;
+      bottom: 30px;
+    }
+  </style>
+  </head>
+  <body>
+    <div class="container">
+      <div class="fixed_block"> fixed block </div>
+      <div class="positioned_fixed_block"> positioned fixed block </div>
+      <div class="sized_fixed_block"> sized fixed block </div>
+    </div>
+  </body>
+</html>
diff --git a/src/test/ref/position_fixed_b.html b/src/test/ref/position_fixed_b.html
new file mode 100644
index 00000000000..1fe3fc1ec45
--- /dev/null
+++ b/src/test/ref/position_fixed_b.html
@@ -0,0 +1,43 @@
+<html>
+  <head>
+    <style>
+    .container {
+      display: block;
+      background: blue;
+    }
+    .fixed_block {
+      background: green;
+      position: fixed;
+    }
+    .positioned_fixed_block {
+      background: yellow;
+      position: fixed;
+      top: 50%;
+      right: 25px;
+    }
+    .sized_fixed_block {
+      background: red;
+      position: fixed;
+      height: 50px;
+      width: 50px;
+      left: 5px;
+      right: 10px;
+      top: 100px;
+      bottom: 30px;
+    }
+    .stretched_fixed_block {
+      position: fixed;
+      background: black;
+      top: 100px;
+      bottom: 30px;
+    }
+  </style>
+  </head>
+  <body>
+    <div class="container">
+      <div class="fixed_block"> fixed block </div>
+      <div class="positioned_fixed_block"> positioned fixed block </div>
+      <div class="sized_fixed_block"> sized fixed block </div>
+    </div>
+  </body>
+</html>