emf-converter

A zero-dependency TypeScript library that converts EMF (Enhanced Metafile) and WMF (Windows Metafile) binary buffers into PNG data URLs by parsing their record streams and replaying the drawing commands onto an HTML Canvas.

Windows Metafiles store a sequence of GDI drawing commands and are commonly embedded inside Office documents (Word, PowerPoint) and Windows clipboard data. This converter reads the raw binary, interprets each record, and replays the drawing operations onto a Canvas to produce a rasterised PNG. It handles three formats:

Format	Description	Coordinate system
WMF	Windows Metafile (16-bit)	Window/viewport mapping
EMF	Enhanced Metafile (32-bit GDI)	Bounds-based scaling
EMF+	GDI+ extension embedded in EMF	World transform matrix

▶️ Live demo · 📦 npm

---

Demo

Try it right in your browser — drop in an .emf or .wmf file and see the rendered PNG, conversion time, and output size:

https://christophervr.github.io/emf-converter/

Install

npm install emf-converter

No dependencies. Requires a Canvas API at runtime — OffscreenCanvas (Web Workers) or HTMLCanvasElement.

Quick start

import { convertEmfToDataUrl, convertWmfToDataUrl } from 'emf-converter';

const emfBuffer: ArrayBuffer = /* loaded from file or network */;
const pngDataUrl = await convertEmfToDataUrl(emfBuffer);
// => "data:image/png;base64,iVBORw0KGgo..."

const wmfPng = await convertWmfToDataUrl(wmfBuffer);

// Optional: limit output dimensions (aspect ratio preserved)
const scaled = await convertEmfToDataUrl(emfBuffer, { maxWidth: 1024, maxHeight: 768 });

Both functions return Promise<string | null> — null if the buffer is invalid or no Canvas API is available.

API

convertEmfToDataUrl(buffer, options?) · convertWmfToDataUrl(buffer, options?)

Parameter	Type	Description
buffer	ArrayBuffer	Raw EMF/WMF file bytes
options	EmfConvertOptions (optional)	Output size, DPI scale, record limits, font mapping
Returns	Promise<string | null>	PNG data URL or null on failure

EmfConvertOptions

Field	Type	Default	Description
maxWidth	number	—	Maximum output width in pixels (aspect ratio preserved)
maxHeight	number	—	Maximum output height in pixels
dpiScale	number	1	Resolution multiplier for sharper output; clamped to 4
maxCanvasDimension	number	8192	Hard cap on canvas width/height in pixels
maxRecords	number	200000/500000	Cap on records processed per stream before replay stops (EMF+ uses the higher default unless overridden)
fontFamilyMap	Record<string, string>	—	Maps Windows face names (case-insensitive) to fonts available locally, e.g. { calibri: 'Carlito' }

const png = await convertEmfToDataUrl(buffer, {
	dpiScale: 2,
	fontFamilyMap: { calibri: 'Carlito', 'ms shell dlg': 'Tahoma' },
});

How it works

A three-phase pipeline: parse → replay → export. The header parser extracts the drawing bounds, a Canvas is created and clamped to 8192×8192 (configurable via maxCanvasDimension), then records are scanned sequentially and dispatched to GDI, EMF+, or WMF handlers that drive the Canvas 2D context. Embedded bitmaps (DIB and GDI+ pixel formats) and recursively embedded metafiles are resolved asynchronously after the synchronous replay completes.

It supports 300+ EMF GDI record types, the EMF+ (GDI+) record set, and legacy WMF records, including state, transforms, objects, shapes, poly/path operations, text, bitmaps, gradients, raster operations, and clipping:

• Clip regions with full boolean combine modes — the converter tracks the active clip as a list of path shapes, so Intersect, Union, Xor, Exclude, Complement, and Replace combine modes work for EMR_INTERSECTCLIPRECT / EMR_EXCLUDECLIPRECT / EMR_EXTSELECTCLIPRGN (all RGN_* modes), the EMF+ SetClipRect / SetClipPath / SetClipRegion records (all CombineMode values, including nested region-node trees), and clip translation via EMR_OFFSETCLIPRGN / EMF+ OffsetClip. Subtraction and symmetric difference are expressed through even-odd fill-rule clipping, which Canvas 2D cannot do with plain clip() stacking.
• Gradient brushes — GDI+ linear gradients render as Canvas linear gradients with their full colour-stop list (preset blend colours and blend factors are expanded into stops, and the optional brush transform rotates the gradient axis). Path gradients render as radial gradients from the centre colour to the surrounding colour across the boundary radius.
• Raster operations (ROP2) — every SetROP2 mode is mapped: R2_BLACK, R2_WHITE, R2_NOP, R2_COPYPEN, R2_NOTCOPYPEN, and R2_NOT are emulated exactly (via colour inversion and difference compositing); the remaining bitwise AND/OR/XOR-family modes are approximated with the nearest arithmetic composite (difference / darken / lighten), combined with pen-colour inversion for the NOT variants.
• GDI world transforms — the scale and translation set by EMR_SETWORLDTRANSFORM / EMR_MODIFYWORLDTRANSFORM are applied to all GDI drawing, which is required for GDI+-exported EMF files (they record coordinates at 16× sub-pixel precision with a compensating transform). EMF+ records support the full affine transform set.

Limitations

• Approximated edge cases in region ops — all six combine modes are exact while the tracked clip is at most one composable shape (the overwhelmingly common case). When the clip is already an intersection of several shapes, or was set from a live path bracket (EMR_SELECTCLIPPATH), Union / Xor / Complement degrade to the nearest conservative approximation (a console log notes when this happens).
• Bitwise ROP2 modes are arithmetic approximations — Canvas compositing cannot reproduce true bitwise AND/OR/XOR against the destination, so those modes use darken / lighten / difference stand-ins; only the modes listed above as exact are pixel-faithful.
• Gradient details — gradient wrap/tile modes clamp instead of tiling, path gradients are radial approximations of the true boundary-shaped falloff, and texture (image) brushes fall back to solid black.
• GDI rotation/skew — rotation and shear components of the GDI world transform are ignored (EMF+ transforms are unaffected); plain-GDI metafiles using rotated world transforms are rare.
• Safety limits — output is clamped to 8192×8192 and replay stops after 200,000 records (EMF/WMF) or 500,000 (EMF+). All three are overridable via maxCanvasDimension / maxRecords.
• Font rendering uses the host Canvas font engine, so glyph metrics may differ from Windows GDI. Weight, italic, underline, and strike-out are honoured; supply fontFamilyMap to remap Windows face names to fonts available in your environment.

License

Apache-2.0 — free for commercial and closed-source use, with an explicit patent grant.