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https://github.com/netsurf-browser/netsurf
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48 lines
2.2 KiB
Plaintext
48 lines
2.2 KiB
Plaintext
HTML processing and layout
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==========================
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The modules in the layout directory process and layout HTML pages.
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Overview
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--------
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This is the process to render an HTML document:
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First the HTML is parsed to a tree of xmlNodes using the HTML parser in libxml.
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This happens simultaneously with the fetch [html_process_data()].
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Any stylesheets which the document depends on are fetched and parsed.
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The tree is converted to a 'box tree' by xml_to_box(). The box tree contains a
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node for each block, inline element, table, etc. The aim of this stage is to
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determine the 'display' or 'float' CSS property of each element, and create the
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corresponding node in the box tree. At this stage the style for each element is
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also calculated (from CSS rules and element attributes). The tree is normalised
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so that each node only has children of permitted types (eg. TABLE_CELLs must be
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within TABLE_ROWs) by adding missing boxes.
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The box tree is passed to the layout engine [layout_document()], which finds the
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space required by each element and assigns coordinates to the boxes, based on
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the style of each element and the available width. This includes formatting
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inline elements into lines, laying out tables, and positioning floats. The
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layout engine can be invoked again on a already laid out box tree to reformat it
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to a new width. Coordinates in the box tree are relative to the position of the
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parent node.
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The box tree can then be rendered using each node's coordinates.
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Absolute positioning
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--------------------
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Absolutely positioned boxes are constructed in the box tree in the same place as
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if they were not absolutely positioned. Inline boxes are created as
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INLINE_BLOCK, tables as TABLE, and other boxes as BLOCK (see
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box_solve_display()).
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During layout, absolutely positioned boxes in block context (BLOCK or TABLE) are
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given a position in layout_block_context(), but treated as having no height. In
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inline context (INLINE_BLOCK), they are given a position in layout_line(), but
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treated as having no width or height. This is done to determine the static
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position.
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An additional pass after main layout positions and layouts all absolutely
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positioned boxes (see layout_position_absolute()).
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