Implement position: absolute for replaced elements.

Add reftests for replaced and nested absolute flows.

src/components/main/layout/block.rs

@@ -10,8 +10,8 @@
 //! The term 'positioned element' refers to elements with position =
 //! 'relative', 'absolute', or 'fixed'.
 
-use layout::box_::Box;
-use layout::construct::{FlowConstructor, OptVector};
+use layout::box_::{Box, ImageBox, ScannedTextBox};
+use layout::construct::FlowConstructor;
 use layout::context::LayoutContext;
 use layout::display_list_builder::{DisplayListBuilder, ExtraDisplayListData};
 use layout::floats::{FloatKind, Floats, PlacementInfo};
@@ -78,6 +78,94 @@ impl WidthConstraintSolution {
             margin_right: margin_right,
         }
     }
+
+    /// Solve the horizontal constraint equation for absolute replaced elements.
+    ///
+    /// `static_x_offset`: total offset of current flow's hypothetical
+    /// position (static position) from its actual Containing Block.
+    ///
+    /// Assumption: The used value for width has already been calculated.
+    ///
+    /// CSS Section 10.3.8
+    /// Constraint equation:
+    /// left + right + width + margin-left + margin-right
+    /// = absolute containing block width - (horizontal padding and border)
+    /// [aka available_width]
+    ///
+    /// Return the solution for the equation.
+    fn solve_horiz_constraints_abs_replaced(width: Au,
+                                            left_margin: MaybeAuto,
+                                            right_margin: MaybeAuto,
+                                            left: MaybeAuto,
+                                            right: MaybeAuto,
+                                            available_width: Au,
+                                            static_x_offset: Au)
+                                            -> WidthConstraintSolution {
+        // TODO: Check for direction of static-position Containing Block (aka
+        // parent flow, _not_ the actual Containing Block) when right-to-left
+        // is implemented
+        // Assume direction is 'ltr' for now
+        // TODO: Handle all the cases for 'rtl' direction.
+
+        // Distance from the left edge of the Absolute Containing Block to the
+        // left margin edge of a hypothetical box that would have been the
+        // first box of the element.
+        let static_position_left = static_x_offset;
+
+        let (left, right, width, margin_left, margin_right) = match (left, right) {
+            (Auto, Auto) => {
+                let left = static_position_left;
+                let margin_l = left_margin.specified_or_zero();
+                let margin_r = right_margin.specified_or_zero();
+                let sum = left + width + margin_l + margin_r;
+                (left, available_width - sum, width, margin_l, margin_r)
+            }
+            // If only one is Auto, solve for it
+            (Auto, Specified(right)) => {
+                let margin_l = left_margin.specified_or_zero();
+                let margin_r = right_margin.specified_or_zero();
+                let sum = right + width + margin_l + margin_r;
+                (available_width - sum, right, width, margin_l, margin_r)
+            }
+            (Specified(left), Auto) => {
+                let margin_l = left_margin.specified_or_zero();
+                let margin_r = right_margin.specified_or_zero();
+                let sum = left + width + margin_l + margin_r;
+                (left, available_width - sum, width, margin_l, margin_r)
+            }
+            (Specified(left), Specified(right)) => {
+                match (left_margin, right_margin) {
+                    (Auto, Auto) => {
+                        let total_margin_val = (available_width - left - right - width);
+                        if total_margin_val < Au(0) {
+                            // margin-left becomes 0 because direction is 'ltr'.
+                            (left, right, width, Au(0), total_margin_val)
+                        } else {
+                            // Equal margins
+                            (left, right, width,
+                             total_margin_val.scale_by(0.5),
+                             total_margin_val.scale_by(0.5))
+                        }
+                    }
+                    (Specified(margin_l), Auto) => {
+                        let sum = left + right + width + margin_l;
+                        (left, right, width, margin_l, available_width - sum)
+                    }
+                    (Auto, Specified(margin_r)) => {
+                        let sum = left + right + width + margin_r;
+                        (left, right, width, available_width - sum, margin_r)
+                    }
+                    (Specified(margin_l), Specified(margin_r)) => {
+                        // Values are over-constrained.
+                        // Ignore value for 'right' cos direction is 'ltr'.
+                        let sum = left + width + margin_l + margin_r;
+                        (left, available_width - sum, width, margin_l, margin_r)
+                    }
+                }
+            }
+        };
+        WidthConstraintSolution::new(left, right, width, margin_left, margin_right)
+    }
 }
 
 /// The solutions for the heights-and-margins constraint equation.
@@ -110,7 +198,7 @@ impl HeightConstraintSolution {
     /// [aka available_height]
     ///
     /// Return the solution for the equation.
-    fn solve_vertical_constraints_abs_position(height: MaybeAuto,
+    fn solve_vertical_constraints_abs_nonreplaced(height: MaybeAuto,
                                                   top_margin: MaybeAuto,
                                                   bottom_margin: MaybeAuto,
                                                   top: MaybeAuto,
@@ -123,7 +211,7 @@ impl HeightConstraintSolution {
         // top margin edge of a hypothetical box that would have been the
         // first box of the element.
         let static_position_top = static_y_offset;
-;
+
         let (top, bottom, height, margin_top, margin_bottom) = match (top, bottom, height) {
             (Auto, Auto, Auto) => {
                 let margin_top = top_margin.specified_or_zero();
@@ -209,6 +297,80 @@ impl HeightConstraintSolution {
         };
         HeightConstraintSolution::new(top, bottom, height, margin_top, margin_bottom)
     }
+
+    /// Solve the vertical constraint equation for absolute replaced elements.
+    ///
+    /// Assumption: The used value for height has already been calculated.
+    ///
+    /// CSS Section 10.6.5
+    /// Constraint equation:
+    /// top + bottom + height + margin-top + margin-bottom
+    /// = absolute containing block height - (vertical padding and border)
+    /// [aka available_height]
+    ///
+    /// Return the solution for the equation.
+    fn solve_vertical_constraints_abs_replaced(height: Au,
+                                               top_margin: MaybeAuto,
+                                               bottom_margin: MaybeAuto,
+                                               top: MaybeAuto,
+                                               bottom: MaybeAuto,
+                                               _: Au,
+                                               available_height: Au,
+                                               static_y_offset: Au)
+                                               -> HeightConstraintSolution {
+        // Distance from the top edge of the Absolute Containing Block to the
+        // top margin edge of a hypothetical box that would have been the
+        // first box of the element.
+        let static_position_top = static_y_offset;
+
+        let (top, bottom, height, margin_top, margin_bottom) = match (top, bottom) {
+            (Auto, Auto) => {
+                let margin_top = top_margin.specified_or_zero();
+                let margin_bottom = bottom_margin.specified_or_zero();
+                let top = static_position_top;
+                let sum = top + height + margin_top + margin_bottom;
+                (top, available_height - sum, height, margin_top, margin_bottom)
+            }
+            (Specified(top), Specified(bottom)) => {
+                match (top_margin, bottom_margin) {
+                    (Auto, Auto) => {
+                        let total_margin_val = (available_height - top - bottom - height);
+                        (top, bottom, height,
+                         total_margin_val.scale_by(0.5),
+                         total_margin_val.scale_by(0.5))
+                    }
+                    (Specified(margin_top), Auto) => {
+                        let sum = top + bottom + height + margin_top;
+                        (top, bottom, height, margin_top, available_height - sum)
+                    }
+                    (Auto, Specified(margin_bottom)) => {
+                        let sum = top + bottom + height + margin_bottom;
+                        (top, bottom, height, available_height - sum, margin_bottom)
+                    }
+                    (Specified(margin_top), Specified(margin_bottom)) => {
+                        // Values are over-constrained. Ignore value for 'bottom'.
+                        let sum = top + height + margin_top + margin_bottom;
+                        (top, available_height - sum, height, margin_top, margin_bottom)
+                    }
+                }
+            }
+
+            // If only one is Auto, solve for it
+            (Auto, Specified(bottom)) => {
+                let margin_top = top_margin.specified_or_zero();
+                let margin_bottom = bottom_margin.specified_or_zero();
+                let sum = bottom + height + margin_top + margin_bottom;
+                (available_height - sum, bottom, height, margin_top, margin_bottom)
+            }
+            (Specified(top), Auto) => {
+                let margin_top = top_margin.specified_or_zero();
+                let margin_bottom = bottom_margin.specified_or_zero();
+                let sum = top + height + margin_top + margin_bottom;
+                (top, available_height - sum, height, margin_top, margin_bottom)
+            }
+        };
+        HeightConstraintSolution::new(top, bottom, height, margin_top, margin_bottom)
+    }
 }
 
 /// The real assign-heights traversal for flows with position 'absolute'.
@@ -424,6 +586,22 @@ impl BlockFlow {
         traversal.process(flow)
     }
 
+    /// Return true if this has a replaced box.
+    ///
+    /// The only two types of replaced boxes currently are text boxes and
+    /// image boxes.
+    fn is_replaced_content(&self) -> bool {
+        match self.box_ {
+            Some(ref box_) => {
+                match box_.specific {
+                    ScannedTextBox(_) | ImageBox(_) => true,
+                    _ => false,
+                }
+            }
+            None => false,
+        }
+    }
+
     pub fn teardown(&mut self) {
         for box_ in self.box_.iter() {
             box_.teardown();
@@ -521,14 +699,28 @@ impl BlockFlow {
                 (MaybeAuto::from_style(style.PositionOffsets.get().left, containing_block_width),
                  MaybeAuto::from_style(style.PositionOffsets.get().right, containing_block_width));
             let available_width = containing_block_width - box_.border_and_padding_horiz();
-            // TODO: Extract this later into a SolveConstraints trait or something
-            let solution = self.solve_horiz_constraints_abs_position(width,
+
+            let solution = if self.is_replaced_content() {
+                // Calculate used value of width just like we do for inline replaced elements.
+                box_.assign_replaced_width_if_necessary(containing_block_width);
+                let width = box_.border_box.get().size.width;
+                WidthConstraintSolution::solve_horiz_constraints_abs_replaced(width,
                                                                               margin_left,
                                                                               margin_right,
                                                                               left,
                                                                               right,
                                                                               available_width,
-                                                                     static_x_offset);
+                                                                              static_x_offset)
+            } else {
+                // TODO: Extract this later into a SolveConstraints trait or something
+                self.solve_horiz_constraints_abs_nonreplaced(width,
+                                                             margin_left,
+                                                             margin_right,
+                                                             left,
+                                                             right,
+                                                             available_width,
+                                                             static_x_offset)
+            };
 
             let mut margin = box_.margin.get();
             margin.left = solution.margin_left;
@@ -614,7 +806,7 @@ impl BlockFlow {
     /// [aka available_width]
     ///
     /// Return the solution for the equation.
-    fn solve_horiz_constraints_abs_position(&self,
+    fn solve_horiz_constraints_abs_nonreplaced(&self,
                                                width: MaybeAuto,
                                                left_margin: MaybeAuto,
                                                right_margin: MaybeAuto,
@@ -623,8 +815,9 @@ impl BlockFlow {
                                                available_width: Au,
                                                static_x_offset: Au)
                                                -> WidthConstraintSolution {
-        // TODO: Check for direction of parent flow (NOT Containing Block)
-        // when right-to-left is implemented.
+        // TODO: Check for direction of static-position Containing Block (aka
+        // parent flow, _not_ the actual Containing Block) when right-to-left
+        // is implemented
         // Assume direction is 'ltr' for now
 
         // Distance from the left edge of the Absolute Containing Block to the
@@ -1358,7 +1551,25 @@ impl BlockFlow {
                  MaybeAuto::from_style(style.PositionOffsets.get().bottom, containing_block_height));
             let available_height = containing_block_height - box_.border_and_padding_vert();
 
-            let solution = HeightConstraintSolution::solve_vertical_constraints_abs_position(
+            let solution = if self.is_replaced_content() {
+                // Calculate used value of height just like we do for inline replaced elements.
+                // TODO: Pass in the containing block height when Box's
+                // assign-height can handle it correctly.
+                box_.assign_replaced_height_if_necessary();
+                // TODO: Right now, this content height value includes the
+                // margin because of erroneous height calculation in Box_.
+                // Check this when that has been fixed.
+                let height_used_val = box_.border_box.get().size.height;
+                HeightConstraintSolution::solve_vertical_constraints_abs_replaced(height_used_val,
+                                                                                  margin_top,
+                                                                                  margin_bottom,
+                                                                                  top,
+                                                                                  bottom,
+                                                                                  content_height,
+                                                                                  available_height,
+                                                                                  static_y_offset)
+            } else {
+                HeightConstraintSolution::solve_vertical_constraints_abs_nonreplaced(
                     height_used_val,
                     margin_top,
                     margin_bottom,
@@ -1366,7 +1577,8 @@ impl BlockFlow {
                     bottom,
                     content_height,
                     available_height,
-                static_y_offset);
+                    static_y_offset)
+            };
 
             let mut margin = box_.margin.get();
             margin.top = solution.margin_top;
@@ -1626,7 +1838,7 @@ impl Flow for BlockFlow {
     fn assign_height(&mut self, ctx: &mut LayoutContext) {
         // Assign height for box if it is an image box.
         for box_ in self.box_.iter() {
-            box_.assign_height();
+            box_.assign_replaced_height_if_necessary();
         }
 
         if self.is_float() {

src/components/main/layout/box_.rs

@@ -166,6 +166,10 @@ impl ImageBoxInfo {
         Au::from_px(image_ref.get().get_size().unwrap_or(Size2D(0,0)).width)
     }
 
+    // Return used value for width or height.
+    //
+    // `dom_length`: width or height as specified in the `img` tag.
+    // `style_length`: width as given in the CSS
     pub fn style_length(style_length: LengthOrPercentageOrAuto,
                         dom_length: Option<Au>,
                         container_width: Au) -> MaybeAuto {
@@ -1455,6 +1459,7 @@ impl Box {
 
     /// Assigns replaced width for this box only if it is replaced content.
     ///
+    /// This assigns only the width, not margin or anything else.
     /// CSS 2.1 § 10.3.2.
     pub fn assign_replaced_width_if_necessary(&self,container_width: Au) {
         match self.specific {
@@ -1502,8 +1507,10 @@ impl Box {
         }
     }
 
-    /// Assign height for image and scanned text boxes.
-    pub fn assign_height(&self) {
+    /// Assign height for this box if it is replaced content.
+    ///
+    /// Ideally, this should follow CSS 2.1 § 10.6.2
+    pub fn assign_replaced_height_if_necessary(&self) {
         match self.specific {
             GenericBox | IframeBox(_) => {
             }

src/components/main/layout/construct.rs

@@ -687,6 +687,13 @@ impl<'a> FlowConstructor<'a> {
 }
 
 impl<'a> PostorderNodeMutTraversal for FlowConstructor<'a> {
+    // Construct Flow based on 'display', 'position', and 'float' values.
+    //
+    // CSS 2.1 Section 9.7
+    //
+    // TODO: This should actually consult the table in that section to get the
+    // final computed value for 'display'.
+    //
     // `#[inline(always)]` because this is always called from the traversal function and for some
     // reason LLVM's inlining heuristics go awry here.
     #[inline(always)]
@@ -718,6 +725,10 @@ impl<'a> PostorderNodeMutTraversal for FlowConstructor<'a> {
                 }
             }
 
+            // Absolutely positioned elements will have computed value of
+            // `float` as 'none' and `display` as per the table.
+            // Currently, for original `display` value of 'inline', the new
+            // `display` value is 'block'.
             (_, _, position::absolute) | (_, _, position::fixed) => {
                 node.set_flow_construction_result(self.build_flow_for_block(node))
             }

src/components/main/layout/inline.rs

@@ -698,7 +698,7 @@ impl Flow for InlineFlow {
         debug!("assign_height_inline: floats in: {:?}", self.base.floats);
         // assign height for inline boxes
         for box_ in self.boxes.iter() {
-            box_.assign_height();
+            box_.assign_replaced_height_if_necessary();
         }
         let scanner_floats = self.base.floats.clone();
         let mut scanner = LineboxScanner::new(scanner_floats);

src/test/ref/basic.list

@@ -38,6 +38,8 @@
 == position_abs_cb_with_non_cb_kid_a.html position_abs_cb_with_non_cb_kid_b.html
 == position_abs_height_width_a.html position_abs_height_width_b.html
 == position_abs_left_a.html position_abs_left_b.html
+== position_abs_nested_a.html position_abs_nested_b.html
+== position_abs_replaced_simple_a.html position_abs_replaced_simple_b.html
 == position_abs_static_y_a.html position_abs_static_y_b.html
 == position_abs_width_percentage_a.html position_abs_width_percentage_b.html
 == position_fixed_a.html position_fixed_b.html

src/test/ref/position_abs_nested_a.html

@@ -0,0 +1,34 @@
+<html>
+  <head>
+    <style>
+      #first {
+      position: relative;
+      width: 90px;
+      height: 90px;
+      border: solid 1px;
+      }
+      #abs {
+      position: absolute;
+      left: 30px;
+      top: 30px;
+      height: 30px;
+      width: 30px;
+      background: blue;
+      }
+      #abs2 {
+      position: absolute;
+      background: green;
+      height: 15px;
+      width: 15px;
+      }
+    </style>
+  </head>
+  <body>
+    <div id="first">
+      <div id="abs">
+	<div id="abs2">
+	</div>
+      </div>
+    </div>
+  </body>
+</html>

src/test/ref/position_abs_nested_b.html

@@ -0,0 +1,36 @@
+<html>
+  <head>
+    <style>
+      #first {
+      width: 90px;
+      height: 90px;
+      border: solid 1px;
+      }
+      .row {
+      width: 90px;
+      height: 30px;
+      }
+      .center {
+      margin-left: 30px;
+      height: 30px;
+      width: 30px;
+      background: blue;
+      }
+      .little-box {
+      height: 15px;
+      width: 15px;
+      background: green;
+      }
+    </style>
+  </head>
+  <body>
+    <div id="first">
+      <div class="row"></div>
+      <div class="center">
+	<div class="little-box">
+	</div>
+      </div>
+      <div class="row"></div>
+    </div>
+  </body>
+</html>

src/test/ref/position_abs_replaced_simple_a.html

@@ -0,0 +1,25 @@
+<html>
+  <head>
+    <style>
+      #first {
+      position: relative;
+      width: 90px;
+      height: 90px;
+      border: solid 1px;
+      }
+      #abs {
+      position: absolute;
+      margin: 0px;
+      top: 30px;
+      right: 30px;
+      bottom: 30px;
+      width: 30px;
+      }
+    </style>
+  </head>
+  <body>
+    <div id="first">
+      <img src="rust_logo.png" width="100" id="abs" alt="Rust Logo" />
+    </div>
+  </body>
+</html>

src/test/ref/position_abs_replaced_simple_b.html

@@ -0,0 +1,32 @@
+<html>
+  <head>
+    <style>
+      #first {
+      width: 90px;
+      height: 90px;
+      border: solid 1px;
+      }
+      .row {
+      width: 90px;
+      height: 30px;
+      }
+      .center {
+      margin-left: 30px;
+      height: 30px;
+      width: 30px;
+      background: green;
+      }
+    </style>
+  </head>
+  <body>
+    <div id="first">
+      <div class="row">
+      </div>
+      <div class="center">
+	<img src="rust_logo.png" width="30" id="abs" alt="Rust Logo" />
+      </div>
+      <div class="row">
+      </div>
+    </div>
+  </body>
+</html>