Floating objects and text wrap

How anchored objects are positioned and how text goes round them. Code: Layout/Floats/, with hooks in the paragraph formatter, the page flow and the painter. DrawingML painting itself is in drawingml-rendering.md.

What floats

Inline drawings are not floats: they take a character's place in the line (drawingml-rendering.md).

Positioning (ECMA-376 Part 1 §20.4.2.10, §20.4.2.11, §20.4.2.13; [MS-ODRAWXML] for wp14)

• Horizontal bases: page, margin, column, character, leftMargin, rightMargin, insideMargin, outsideMargin. Vertical bases: page, margin, paragraph, line, topMargin, bottomMargin, insideMargin, outsideMargin (inside is the top, outside the bottom). Inside and outside follow the printed page number: page 1 is a right-hand page, so inside is the left margin.
• The offset (posOffset, or wp14:pctPosHOffset/pctPosVOffset as a fraction of the base) or the alignment (left, center, right, inside, outside; top, center, bottom) is applied to the base. simplePos overrides it with page coordinates.
• wp14:sizeRelH/sizeRelV with a percentage replace the stated extent: width and height are that fraction of the named base.
• Base paragraph is the top of the anchor paragraph's first line (after its space before); line is the top of the line that holds the anchor; character is the left edge of the column (the anchor's own x is not known before the lines are cut).
• An object positioned relative to the text stays on its page: when it would run off the bottom it is moved up. Page-relative objects are not moved. An object positioned from the text also stays above the footnote area of its column as far as the notes are known when it is anchored (the note reservation is lowered into the body's bottom edge); notes that grow afterwards can still reach it.
• allowOverlap="0": an object that would overlap an earlier one that also may not overlap is moved below it, if the page allows.
• locked and layoutInCell do not change layout, except that an object in a table cell is placed from the cell when layoutInCell is on (default) and from the page otherwise; text in the cell does not wrap around it.
• The object belongs to the page its anchor paragraph's first line is on. A paragraph that moves to the next page (keep with next, keep lines, widow control, a page break) takes its objects with it.

Wrapping

• Text is cut into rows; where an object takes part of the width, a row becomes segments of free space, each filled like a line of its own. The segments of one row are consecutive LayoutLines of the paragraph that share a baseline and height (the second and later have SameRow internally; in the tree they have equal Baseline). A row is cut again when its height (the tallest segment's) moves it into or out of an object's band.
• wrapSquare: the box plus distT/distB/distL/distR (and effectExtent). wrapTight/wrapThrough: the extent of the wrap polygon (21600ths of the object's size) or, without one, of the shape's own outline, on each row, plus the side distances; concave parts are not entered (through is treated as tight). wrapTopAndBottom: nothing beside the object; text resumes below it plus distB. wrapNone: no effect on text; the object is painted behind (behindDoc) or in front.
• wrapText: bothSides fills every segment, left/right blocks everything on the other side of the object, largest keeps the widest segment of the row.
• A segment narrower than 12 pt is left empty (FloatSpace.MinimumSegment). If no segment is wide enough the rows move down to the nearest object edge.
• A display equation has a row to itself. Where an object splits the row, it takes the widest free stretch and nothing else shares its baseline; an inline equation is an unbreakable atom and goes into whichever stretch has room for it. Which of these Word does is listed with the points to check below.
• Space skipped above a row (under a top-and-bottom object, or beside one too wide for text) is GapBefore on the row's first line, so the page flow and the tree see lines at their real positions.
• Paragraphs are cut around the objects already on the page and the ones the paragraph itself anchors. A paragraph that is cut again on a later page keeps the lines already placed.
• Objects in headers and footers are painted but do not wrap body text. Text in table cells does not wrap around objects.

Painting

LayoutPage.Floats lists the placed objects (LayoutFloat: Bounds, Wrap, BehindText, ZOrder, AltText, AnchorParagraph). The painter draws, in order: decorations, the objects behind the text (by relativeHeight, then anchor order), the blocks, the objects in front. Objects of a header or footer are artifacts.

Frames and drop caps

• Consecutive paragraphs with equal framePr form one frame, laid out at its width (w; without one, the width its text needs up to the column), stacked with paragraph spacing, at the frame's position. hRule exact and atLeast set its height. The frame takes no room in the flow.
• A drop cap is formatted from the paragraph with dropCap drop or margin and set when the paragraph after it is placed. Its baseline is the baseline of the last of its lines lines; the lines it spans start to its right (hSpace away).

Notes and limits

layout.anchored-drawing-unwrapped and layout.table-floating are gone. VML groups, v:group and w:object stay unlaid (layout.drawing-skipped).

Points that need Word's own output at the 1.0 gate: where a display equation goes beside an object, the minimum segment width, the paragraph and line bases (space before and the line top), where a drop cap's box ends, the frame width when none is given, and how Word treats tight wrapping without a polygon.

Known gaps: paragraphs already placed on a page do not move when a later anchor positions an object over them; rotated objects wrap by their unrotated box; a floating table does not wrap text that came before it in the document; text frames do not split across pages; floats anchored in text boxes, headers and cells do not wrap body text.