Change the resume_at and skip_stack structure

Many operations, including page breaks, require a pointer to a specific
position of the box tree. For example, we used to have this structure to point
to the beginning of the first child of the second child:

(1, (2, None))

We now use:

{1: {2: None}}

This change is the first step to handle parallel flows (see #36). It doesn’t
change anything to the layout for now, but it allows us to store multiple
pointers in the same structure.

The next step is to handle multiple pointers in skip_stack during boxes layout.
It means that most of the *_layout() function need an extra for-loop to manage
multiple skip stacks.

We’ll then need to split new types of boxes: table cells, floats, absolutes…

tests/test_text.py

@@ -28,10 +28,10 @@ def test_line_content():
     for width, remaining in [(100, 'text for test'),
                              (45, 'is a text for test')]:
         text = 'This is a text for test'
-        _, length, resume_at, _, _, _ = make_text(
+        _, length, resume_index, _, _, _ = make_text(
             text, width, font_family=SANS_FONTS.split(','), font_size=19)
-        assert text[resume_at:] == remaining
-        assert length + 1 == resume_at  # +1 is for the removed trailing space
+        assert text[resume_index:] == remaining
+        assert length + 1 == resume_index  # +1 for the removed trailing space
 
 
 @assert_no_logs
@@ -46,16 +46,16 @@ def test_line_breaking():
     string = 'Thïs is a text for test'
 
     # These two tests do not really rely on installed fonts
-    _, _, resume_at, _, _, _ = make_text(string, 90, font_size=1)
-    assert resume_at is None
+    _, _, resume_index, _, _, _ = make_text(string, 90, font_size=1)
+    assert resume_index is None
 
-    _, _, resume_at, _, _, _ = make_text(string, 90, font_size=100)
-    assert string.encode('utf-8')[resume_at:].decode('utf-8') == (
+    _, _, resume_index, _, _, _ = make_text(string, 90, font_size=100)
+    assert string.encode('utf-8')[resume_index:].decode('utf-8') == (
         'is a text for test')
 
-    _, _, resume_at, _, _, _ = make_text(
+    _, _, resume_index, _, _, _ = make_text(
         string, 100, font_family=SANS_FONTS.split(','), font_size=19)
-    assert string.encode('utf-8')[resume_at:].decode('utf-8') == (
+    assert string.encode('utf-8')[resume_index:].decode('utf-8') == (
         'text for test')
 
 
@@ -64,11 +64,11 @@ def test_line_breaking_rtl():
     string = 'لوريم ايبسوم دولا'
 
     # These two tests do not really rely on installed fonts
-    _, _, resume_at, _, _, _ = make_text(string, 90, font_size=1)
-    assert resume_at is None
+    _, _, resume_index, _, _, _ = make_text(string, 90, font_size=1)
+    assert resume_index is None
 
-    _, _, resume_at, _, _, _ = make_text(string, 90, font_size=100)
-    assert string.encode('utf-8')[resume_at:].decode('utf-8') == (
+    _, _, resume_index, _, _, _ = make_text(string, 90, font_size=100)
+    assert string.encode('utf-8')[resume_index:].decode('utf-8') == (
         'ايبسوم دولا')
 
 

weasyprint/formatting_structure/build.py

@@ -1489,12 +1489,12 @@ def _inner_block_in_inline(box, skip_stack=None):
     if is_start:
         skip = 0
     else:
-        skip, skip_stack = skip_stack
+        (skip, skip_stack), = skip_stack.items()
 
     for i, child in enumerate(box.children[skip:]):
         index = i + skip
-        if isinstance(child, boxes.BlockLevelBox) and \
-                child.is_in_normal_flow():
+        if (isinstance(child, boxes.BlockLevelBox) and
+                child.is_in_normal_flow()):
             assert skip_stack is None  # Should not skip here
             block_level_box = child
             index += 1  # Resume *after* the block
@@ -1511,7 +1511,7 @@ def _inner_block_in_inline(box, skip_stack=None):
                 changed = True
             new_children.append(new_child)
         if block_level_box is not None:
-            resume_at = (index, resume_at)
+            resume_at = {index: resume_at}
             box = box.copy_with_children(new_children)
             break
     else:

weasyprint/layout/__init__.py

@@ -152,8 +152,7 @@ def layout_document(html, root_box, context, max_loops=8):
     watch_elements_after = []
     for i, page in enumerate(pages):
         # We need the updated page_counter_values
-        resume_at, next_page, right_page, page_state, remake_state = (
-            context.page_maker[i + 1])
+        _, _, _, page_state, _ = context.page_maker[i + 1]
         page_counter_values = page_state[1]
 
         for child in page.descendants():

weasyprint/layout/blocks.py

@@ -101,7 +101,6 @@ def block_box_layout(context, box, max_position_y, skip_stack,
         result = columns_layout(
             context, box, max_position_y, skip_stack, containing_block,
             page_is_empty, absolute_boxes, fixed_boxes, adjoining_margins)
-
         resume_at = result[1]
         # TODO: this condition and the whole relayout are probably wrong
         if resume_at is None:
@@ -115,25 +114,24 @@ def block_box_layout(context, box, max_position_y, skip_stack,
                     context, box, max_position_y, skip_stack,
                     containing_block, page_is_empty, absolute_boxes,
                     fixed_boxes, adjoining_margins)
-
         return result
     elif box.is_table_wrapper:
         table_wrapper_width(
             context, box, (containing_block.width, containing_block.height))
     block_level_width(box, containing_block)
 
-    new_box, resume_at, next_page, adjoining_margins, collapsing_through = \
-        block_container_layout(
-            context, box, max_position_y, skip_stack, page_is_empty,
-            absolute_boxes, fixed_boxes, adjoining_margins, discard)
+    result = block_container_layout(
+        context, box, max_position_y, skip_stack, page_is_empty,
+        absolute_boxes, fixed_boxes, adjoining_margins, discard)
+    new_box = result[0]
     if new_box and new_box.is_table_wrapper:
         # Don't collide with floats
         # http://www.w3.org/TR/CSS21/visuren.html#floats
         position_x, position_y, _ = avoid_collisions(
             context, new_box, containing_block, outer=False)
         new_box.translate(
             position_x - new_box.position_x, position_y - new_box.position_y)
-    return new_box, resume_at, next_page, adjoining_margins, collapsing_through
+    return result
 
 
 @handle_min_max_width
@@ -316,10 +314,9 @@ def block_container_layout(context, box, max_position_y, skip_stack,
         skip = 0
         first_letter_style = getattr(box, 'first_letter_style', None)
     else:
-        skip, skip_stack = skip_stack
+        (skip, skip_stack), = skip_stack.items()
         first_letter_style = None
-    for i, child in enumerate(box.children[skip:]):
-        index = i + skip
+    for index, child in enumerate(box.children[skip:], start=(skip or 0)):
         child.position_x = position_x
         # XXX does not count margins in adjoining_margins:
         child.position_y = position_y
@@ -356,7 +353,7 @@ def block_container_layout(context, box, max_position_y, skip_stack,
                         if result:
                             new_children, resume_at = result
                             break
-                    resume_at = (index, None)
+                    resume_at = {index: None}
                     break
             elif child.is_running():
                 running_name = child.style['position'][1]
@@ -419,7 +416,7 @@ def block_container_layout(context, box, max_position_y, skip_stack,
                         # Remove lines to keep them for the next page
                         del new_children[-needed:]
                     # Page break here, resume before this line
-                    resume_at = (index, skip_stack)
+                    resume_at = {index: skip_stack}
                     is_page_break = True
                     break
                 # TODO: this is incomplete.
@@ -444,7 +441,7 @@ def block_container_layout(context, box, max_position_y, skip_stack,
                         break
 
             if new_children:
-                resume_at = (index, new_children[-1].resume_at)
+                resume_at = {index: new_children[-1].resume_at}
             if is_page_break:
                 break
         else:
@@ -462,7 +459,7 @@ def block_container_layout(context, box, max_position_y, skip_stack,
                         'page', 'left', 'right', 'recto', 'verso'):
                     page_name = child.page_values()[0]
                     next_page = {'break': page_break, 'page': page_name}
-                    resume_at = (index, None)
+                    resume_at = {index: None}
                     break
             else:
                 page_break = 'auto'
@@ -589,7 +586,7 @@ def block_container_layout(context, box, max_position_y, skip_stack,
                     new_children = []
 
                 if new_children:
-                    resume_at = (index, None)
+                    resume_at = {index: None}
                     break
                 else:
                     # This was the first child of this box, cancel the box
@@ -602,7 +599,7 @@ def block_container_layout(context, box, max_position_y, skip_stack,
             # TODO: back-track somehow when all lines fit but not borders
             new_children.append(new_child)
             if resume_at is not None:
-                resume_at = (index, resume_at)
+                resume_at = {index: resume_at}
                 break
     else:
         resume_at = None
@@ -817,7 +814,7 @@ def find_earlier_page_break(children, absolute_boxes, fixed_boxes):
         if index < orphans:
             return None
         new_children = children[:index]
-        resume_at = (0, new_children[-1].resume_at)
+        resume_at = {0: new_children[-1].resume_at}
         remove_placeholders(children[index:], absolute_boxes, fixed_boxes)
         return new_children, resume_at
 
@@ -838,7 +835,7 @@ def find_earlier_page_break(children, absolute_boxes, fixed_boxes):
                 index += 1  # break after child
                 new_children = children[:index]
                 # Get the index in the original parent
-                resume_at = (children[index].index, None)
+                resume_at = {children[index].index: None}
                 break
             previous_in_flow = child
 
@@ -862,7 +859,7 @@ def find_earlier_page_break(children, absolute_boxes, fixed_boxes):
                                 new_children.append(next_child)
 
                     # Index in the original parent
-                    resume_at = (new_child.index, resume_at)
+                    resume_at = {new_child.index: resume_at}
                     index += 1  # Remove placeholders after child
                     break
     else:

weasyprint/layout/flex.py

@@ -261,7 +261,7 @@ def flex_layout(context, box, max_position_y, skip_stack, containing_block,
                     child.padding_top + child.padding_bottom)
                 if getattr(box, axis) == 'auto' and (
                         child_height + box.height > available_main_space):
-                    resume_at = (i, None)
+                    resume_at = {i: None}
                     children = children[:i + 1]
                     break
                 box.height += child_height
@@ -844,8 +844,10 @@ def flex_layout(context, box, max_position_y, skip_stack, containing_block,
                     page_is_empty, absolute_boxes, fixed_boxes,
                     adjoining_margins=[], discard=False)[:2]
                 if new_child is None:
-                    if resume_at and resume_at[0]:
-                        resume_at = (resume_at[0] + i - 1, None)
+                    if resume_at:
+                        index, = resume_at
+                        if index:
+                            resume_at = (index + i - 1, None)
                 else:
                     box.children.append(new_child)
                     if child_resume_at is not None:
@@ -854,8 +856,8 @@ def flex_layout(context, box, max_position_y, skip_stack, containing_block,
                         else:
                             first_level_skip = 0
                         if resume_at:
-                            first_level_skip += resume_at[0]
-                        resume_at = (first_level_skip + i, child_resume_at)
+                            first_level_skip += tuple(resume_at)[0]
+                        resume_at = {first_level_skip + i: child_resume_at}
                 if resume_at:
                     break