craft-libs/crates/metafile

craft-metafile

Windows metafiles for the Craft apps: one reader for WMF, EMF and EMF+, and writers for EMF and WMF.

• parse(bytes) -> Picture plays a file's records on a model of the GDI device context and returns what was drawn: paths, pattern fills, bitmaps and text, each with its clip.
• size(bytes) gives the picture's size from the header alone when the header decides it.
• sniff(bytes) -> Option<Kind> and is_metafile(bytes) recognise the formats.
• Picture::fit and Picture::place fit a picture (with crop fractions) into a rectangle for callers that draw it; crop_window is the crop rule they share with bitmaps.
• write::emf and write::wmf (feature write) write a list of drawing operations.

The crate depends on kurbo, thiserror and image (PNG, JPEG, GIF, TIFF and BMP decoders, for the image files that EMF+ and BI_JPEG/BI_PNG bitmaps carry). It knows no fonts, no file system and no application.

The model

A Picture has a size (points when the file states one: the EMF frame, the placeable WMF box; device or logical units otherwise) and items in paint order, in 0..width by 0..height, y down:

Item	What it holds
Item::Path	Segments (Seg: move, line, cubic, close), a fill colour, a stroke colour and width (0 is a hairline), the stroke's LineStyle (cap, join, miter limit, dashes), the fill rule.
Item::Pattern	A path filled with a repeating RGBA Tile: hatch and bitmap brushes, EMF+ gradients and textures. Fills with the same brush share one tile.
Item::Bitmap	RGBA8 pixels (straight alpha, rows top-down), the rectangle they fill and a transform that also holds a turn or a skew (then the rectangle is the box around it).
Item::Text	The string, the font the file asks for (family, height, weight, italic, underline, strike, character set), per-character advances, colours, alignment and a transform from text space.

Every item carries the clip it was drawn under: region (the GDI clip region as rectangles) and clips (clip paths from SELECTCLIPPATH, outermost first; items under the same clip share one Arc<ClipPath>). An item shows inside its region and inside each of its clip paths.

Picture::skipped_records counts records of a type the reader does not play, so a caller can say that part of a file was not read.

Why this model

The three apps had two output models. WordCraft's and DeckCraft's readers produced a picture of paths, bitmaps and text to draw. VectorCraft's reader built VectorCraft document nodes directly, and kept what an editor needs and a renderer can lose: the pen's caps, joins and dashes, clip paths as clips, and the turn of an image. The shared model is the picture, extended with exactly those three things (LineStyle, ClipPath, Item::Bitmap::transform), so an editor can rebuild objects from it and a renderer can draw it. Bitmaps are decoded RGBA rather than raw DIB bytes because every caller needs pixels (two draw them, one re-encodes them as PNG), and because the decoder is where the size, pixel and work limits have to be enforced.

Records read

WMF (MS-WMF)

Group	Records
Headers	Placeable header, memory and disk metafile headers.
Mapping	SETMAPMODE, SETWINDOWORG, SETWINDOWEXT, SETVIEWPORTORG, SETVIEWPORTEXT, all map modes (text, metric, isotropic, anisotropic). A placeable file is played into its box the way Office plays it.
State	SAVEDC, RESTOREDC, SETPOLYFILLMODE, SETROP2, SETBKMODE, SETBKCOLOR, SETTEXTCOLOR, SETTEXTALIGN.
Objects	CREATEPENINDIRECT (style, cap and join bits), CREATEBRUSHINDIRECT (solid, null, hatched), DIBCREATEPATTERNBRUSH, CREATEFONTINDIRECT, SELECTOBJECT, DELETEOBJECT, stock objects. CREATEPALETTE, CREATEPATTERNBRUSH and CREATEREGION take their handle slot.
Drawing	MOVETO, LINETO, POLYLINE, POLYGON, POLYPOLYGON, RECTANGLE, ROUNDRECT, ELLIPSE, ARC, PIE, CHORD, PATBLT.
Bitmaps	STRETCHDIB, DIBSTRETCHBLT, DIBBITBLT (with or without a source).
Text	EXTTEXTOUT (rectangle, opaque, clipped, dx), TEXTOUT; code pages 1250, 1251, 1252, the symbol character set, double-byte lead bytes as blanks.
Clipping	INTERSECTCLIPRECT, EXCLUDECLIPRECT.
Not read	OFFSETWINDOWORG, OFFSETVIEWPORTORG, SCALEWINDOWEXT, SCALEVIEWPORTEXT, flood fills, SETPIXEL, region records (FILLREGION, FRAMEREGION, PAINTREGION, INVERTREGION, SELECTCLIPREGION, OFFSETCLIPRGN), the device-dependent BITBLT, STRETCHBLT and SETDIBTODEV. They are counted in skipped_records.

EMF (MS-EMF)

Group	Records
Header	Frame, device size in pixels, millimetres and (when present) micrometres.
Mapping	SETMAPMODE, window and viewport origin and extent, SCALEVIEWPORTEXTEX, SCALEWINDOWEXTEX, SETWORLDTRANSFORM, MODIFYWORLDTRANSFORM.
State	SAVEDC, RESTOREDC, SETPOLYFILLMODE, SETROP2, SETBKMODE, SETBKCOLOR, SETTEXTCOLOR, SETTEXTALIGN, SETMITERLIMIT, SETARCDIRECTION.
Objects	CREATEPEN, EXTCREATEPEN (cosmetic and geometric, cap, join, user-style dashes), CREATEBRUSHINDIRECT, CREATEMONOBRUSH, CREATEDIBPATTERNBRUSHPT, EXTCREATEFONTINDIRECTW, SELECTOBJECT, DELETEOBJECT, stock objects.
Drawing	MOVETOEX, LINETO, POLYLINE(16), POLYLINETO(16), POLYGON(16), POLYBEZIER(16), POLYBEZIERTO(16), POLYPOLYLINE(16), POLYPOLYGON(16), RECTANGLE, ROUNDRECT, ELLIPSE, ARC, CHORD, PIE.
Paths	BEGINPATH, ENDPATH, CLOSEFIGURE, FILLPATH, STROKEPATH, STROKEANDFILLPATH, ABORTPATH, SELECTCLIPPATH (RGN_AND, RGN_COPY).
Bitmaps	BITBLT, STRETCHBLT, STRETCHDIBITS, SETDIBITSTODEVICE, ALPHABLEND (constant and per-pixel alpha); source-less raster operations fill with the brush, black or white; SRCAND, SRCPAINT and SRCINVERT are drawn as they look over white.
Text	EXTTEXTOUTA, EXTTEXTOUTW, SMALLTEXTOUT; glyph-index strings are left out.
Clipping	INTERSECTCLIPRECT, EXCLUDECLIPRECT, EXTSELECTCLIPRGN (all five modes, on rectangles), SELECTCLIPPATH.
Not read	ANGLEARC, ARCTO, POLYDRAW(16), SETPIXELV, flood fills, region paints, MASKBLT, PLGBLT, TRANSPARENTBLT, GRADIENTFILL, POLYTEXTOUT, WIDENPATH, SETMETARGN, OFFSETCLIPRGN, SETLAYOUT, SELECTCLIPPATH with RGN_OR, RGN_XOR or RGN_DIFF (the clip stays as it was). Unknown types are counted in skipped_records.

EMF+ (MS-EMFPLUS)

An EMF+ only file is played from its EMF+ records. A dual file is played from its EMF records.

Feature	Read
Objects	Brushes (solid, hatch, texture, linear gradient with preset colours or blend factors, path gradient), pens (colour and width), paths, regions, images, fonts, string formats; objects continued over several records.
Drawing	FillRects, DrawRects, FillPolygon, DrawLines, FillEllipse, DrawEllipse, FillPie, DrawPie, DrawArc, FillPath, DrawPath, DrawBeziers, DrawCurve, DrawClosedCurve, FillClosedCurve, FillRegion, Clear.
Images	DrawImage, DrawImagePoints: raw pixel formats, PNG, JPEG, GIF, TIFF and BMP payloads, and nested metafiles (three levels).
Text	DrawString (alignment, wrapping to the layout width), DrawDriverString with character codes, and with glyph indices in the Windows core fonts.
State	World and page transforms, Save, Restore, containers.
Clipping	SetClipRect, SetClipPath, SetClipRegion, ResetClip, OffsetClip: rectangles and convex shapes cut the drawing itself; other shapes clip to their bounding rectangle; region nodes combine by intersect and union.
Not read	Pen caps, joins and dashes (EMF+ strokes have the default line style), image attributes and effects, glyph indices of other fonts, region XOR, exclude and complement, rendering hints, SetRenderingOrigin, the terminal-server records.

Bitmaps (DIB)

BITMAPINFOHEADER and larger headers at 1, 4, 8, 16, 24 and 32 bits with BI_RGB or BI_BITFIELDS; BITMAPCOREHEADER at 1, 4, 8 and 24 bits; BI_JPEG and BI_PNG. Bottom-up and top-down rows, source rectangles (only the rows and columns a record draws are decoded), mirrored destinations. RLE compression is not decoded.

Writers (feature write)

write::emf(ops, region, app, title) and write::wmf(ops, region) take write::Ops in points, y down, in paint order: Fill (path, fill rule, colour), Stroke (path and Pen: colour, width, cap, join, miter limit, dashes), Image (RGBA pixels, an affine placement, an opacity), Clip and Unclip. region is the part of that space the picture covers.

• EMF keeps curves, writes geometric pens (EXTCREATEPEN; dashes as PS_USERSTYLE when the pen can draw them, else one line per dash), path clips inside SAVEDC/RESTOREDC, opaque images as STRETCHDIBITS and translucent ones as ALPHABLEND, each under a world transform.
• WMF flattens curves, writes 16-bit coordinates behind a placeable header (at most 1440 units an inch, fewer for large pictures), and returns what it could not hold in write::Wmf (translucent_images, turned_images, clips_ignored, oversized_images).

The reader reads back what the writers write; the tests round-trip both formats.

Limits

Every size, count and offset from a file is checked before it is used, with get and checked arithmetic. Past a limit the reader keeps what it has (a shorter picture) or leaves the item out; it never panics and never allocates from an unchecked count. Each limit has a test.

Limit	Value	Past it
Items in a picture	200,000	The parse stops.
Bytes of path points and pixels kept (pattern brushes and clip paths included)	256 MiB	The parse stops.
Points in one path bracket; points in one record	2,000,000	The bracket stops growing; the record is left out.
Object table slots	4,096	The object is not stored.
SAVEDC depth	1,024	The parse stops.
Clip paths nested on one device context	32	The parse stops.
Rectangles in a clip region	64	Further rectangles are dropped (this can only hide drawing).
Pen style entries	16	Further entries are dropped.
Pixels in one bitmap	40,000,000	The bitmap is left out.
Bitmap side drawn	30,000	The bitmap is left out before it is decoded.
JPEG or PNG side	32,768	The image is left out before it is decoded.
JPEG and PNG pixels decoded in one file	2^28	Further images are left out before they are decoded.
Pattern tile side	256	The brush is not made.
Characters in one string	16,384 (EMF+: 32,768)	The string is cut.
EMF+ objects, save stack	64, 64	Ignored.
EMF+ points in one record; region nodes	100,000	The list is cut; the region is not made.
EMF+ region depth	32	The region is not made.
EMF+ gradient stops	256	The count is cut.
EMF+ continued object	64 MiB	The size is cut; nothing is reserved ahead.
Nested metafiles	3 levels	The inner picture is not read.
Clipping work per item, and per clip area	1,000,000 and 4,000,000 steps	The item is left out; the clip keeps its previous area.
Masking a bitmap to a clip that is not a rectangle	5,000,000 point tests	The bitmap is left out.
Placed path elements (Picture::place)	500,000	Placing stops.
Placed coordinates (Picture::place)	±1,000,000	The item is left out.
Writers: dashes cut from one stroke	100,000	The stroke is written solid.
Writers: segments from one curve	about 4,096	The tolerance is raised.

The tests parse every prefix of sample files, files with each byte replaced, and random bytes.

What stays in the apps

• Mapping a Picture onto the app's document: VectorCraft builds paths, clipping groups, images and point type from the items (joining consecutive lines into one path, dropping a clip that covers the whole frame, turning skipped records and hatch and pattern fills into its warnings); WordCraft and DeckCraft keep a picture as a picture.
• Drawing: rasterising and PDF output of placed items, font lookup, shaping and glyph drawing (Text only names a font), caching of parsed pictures.
• For the writers: walking the document into write::Ops. Gradients, pattern fills, type as outlines, stroke alignment, width profiles, arrowheads, effects and opacity are decided there, as is scaling an image down before it is written and the wording of any warning.

Origin

Part	From
The reader (canvas, emf, wmf, geom, place, bytes)	DeckCraft crates/metafile at cf0d7fbb, itself ported from WordCraft at 05679497.
EMF+ (emfplus), clip regions (clip, cliprect), text (text), pattern and hatch brushes	DeckCraft.
The cropped, depth-once DIB decoder (dib), the bitmap side cap, size, crop_window, the free-slot object table, capacity-based budget charging, the exact reservation for poly-polygon groups	WordCraft crates/metafile at 639b8133, merged three ways over the common ancestor.
LineStyle, clip paths, Item::Bitmap::transform, skipped_records, the records behind them (EXTCREATEPEN entries, SETMITERLIMIT, SETARCDIRECTION, SCALEVIEWPORTEXTEX, SCALEWINDOWEXTEX, SELECTCLIPPATH, ABORTPATH), closing figures in STROKEANDFILLPATH, the micrometre device size, core-header, JPEG and PNG bitmaps, the per-file decode budget	VectorCraft crates/metafile at 3deafc24 (its reader's behaviour, written anew on this model).
The writers (write)	VectorCraft crates/metafile (emf.rs, wmf.rs, the encoding half of dib.rs, vectorcraft_geom::flatten).

All three sources are MIT OR Apache-2.0. The tests build every file they read in code; the crate bundles no sample files.

Migration

DeckCraft (deckcraft-metafile)

Before	After
deckcraft_metafile::{parse, is_metafile, Picture, Item, Seg, Tile, Text, Font, HAlign, VAlign, SYMBOL_CHARSET, PlacedItem, MAX_BITMAP_SIDE, Error}	The same names in craft_metafile.
Item::Path { segs, fill, stroke, even_odd, region }	Adds line and clips. Draw line when stroking; clip to each of clips as to region.
Item::Bitmap { rect, .. }, Item::Pattern { .. }, Text	Add clips; Item::Bitmap adds transform (equal to rect unless the bitmap is turned).
PlacedItem::*	Add clips (PlacedClip: a path and its fill rule); Path adds line; Bitmap adds transform.
Picture { width, height, items }	Adds skipped_records.
Picture::fit with crops clamped to 95% a side	crop_window: each axis keeps at least 0.5%.

WordCraft (wordcraft-metafile)

Before	After
parse, size, is_metafile, Picture, Seg, Error, MAX_BITMAP_SIDE, crop_window, Picture::{has_size, fit, place}, Item::take_pixels	The same names in craft_metafile.
Item::Path, Item::Bitmap	Add region, clips, line, transform as above; new Item::Pattern (hatch and pattern brushes now draw).
Text { text, x, y, size, cell, font, bold, italic, color, angle, halign, valign, dx }	Text { transform, text, dx, font: Font { family, height, weight, italic, .. }, color, background, h_align, v_align, clip, region, clips }. The reference point and angle are in transform; size is font.height.abs() in text units and cell is font.height > 0; bold is font.weight >= 600. A height of 0 and an empty family are the file's "default font": WordCraft's 16-unit Arial default moves to WordCraft.
Text::layout, TextLayout	Stay in WordCraft, over the shared Text.
PlacedItem::Text { index, tf }	PlacedItem::Text { index, transform, clip, region, clips }.
Text from EXTTEXTOUTW only	Also EXTTEXTOUTA, SMALLTEXTOUT, WMF text, opaque backgrounds, EMF+ strings.

VectorCraft (vectorcraft-metafile)

Before	After
sniff, Kind	craft_metafile::{sniff, Kind}.
import(bytes) -> Imported { document, kind, warnings }	craft_metafile::parse(bytes), then VectorCraft's own mapping of Picture to a Document: Item::Path to a path node (line to cap, join, miter limit and dash), clips to clipping groups (Arc::ptr_eq groups items), region to a rectangle clip, Item::Bitmap to an image placed by transform, Item::Text to point type, Item::Pattern to its tile or a flat colour, skipped_records to the warning.
export(doc, region, kind) -> Output	VectorCraft's scene walk produces craft_metafile::write::Ops, then write::emf(&ops, region, "VectorCraft", &doc.title) or write::wmf(&ops, region); Wmf's flags become the two WMF warnings.
scene::Pen { cap: LineCap, join: LineJoin, dash: Option<Dash> }	write::Pen { cap: Cap, join: Join, dash: Option<write::Dash> } (Cap::Flat is LineCap::Butt). A dash with align_corners, or one Dash::emf_pen_draws refuses, is cut by VectorCraft and passed as the path with no dash, to keep its own dash cutting.
dib::Rgba::fitted, to_png	Stay in VectorCraft.
EMF+ only files: a warning and nothing imported	They are read.