iOS vs Android

The JavaScript API is the same on both platforms, but the drawing engines are not. iOS hands the work to Apple's PencilKit. Android uses a custom view that draws each stroke as Bezier curves whose width follows the speed of your finger. This page collects the differences in one place.

Rendering

	iOS	Android
Engine	PKCanvasView from PencilKit	Custom View drawing into an offscreen bitmap
Line width	PencilKit's own pressure and speed response. The tool width is the midpoint of penMinWidth and penMaxWidth.	max(penMaxWidth / (velocity + 1), penMinWidth), velocity in dp per ms. Slow is thick, fast is thin.
velocityFilterWeight	Ignored	Smooths the velocity between samples (default 0.7)
defaultInkType	pen, marker, pencil; monoline, fountainPen, watercolor, crayon on iOS 17+ (falls back to pen earlier)	Ignored
Stylus	Apple Pencil pressure and tilt affect the ink	Treated like a finger, except for pencilOnly

Why Android has its own renderer

Android has no system ink engine comparable to PencilKit. The Android view is a native port of the well-known velocity-based approach used by signature pads: each new touch sample adds a cubic Bezier segment built from the last four points, and the width changes gradually from the start to the end of each segment. Strokes are drawn into a bitmap, so a finished stroke costs nothing to redraw while you keep writing.

You can try a JavaScript version of the same algorithm on the Props page.

Defaults

Prop	iOS	Android
penColor	black	#111111
toolbarHeight	44	48
toolbarTintColor	The view's tint color (system blue)	Each icon's own color. See Toolbar colors.
baselineColor	System gray at 50% opacity	#80808080
baselineOffsetFromBottom	8	16
baselineWidth with baselineStyle="dotted"	1.5	2

Set these props explicitly if you want both platforms to look the same.

History

	iOS	Android
What undo() reverts	The last stroke, clear() or setStrokeData()	The last stroke
clear()	Can be undone	Cannot be undone; also empties the redo stack
setStrokeData()	Can be undone	The previous drawing is gone; undo() removes the restored strokes one by one
New stroke	Empties the redo stack	Empties the redo stack

Exports

	iOS	Android
PNG background	Always transparent	backgroundColor if set
saveToPhotoLibrary PNG	Opaque, white if no backgroundColor	backgroundColor if set, otherwise transparent
Clipboard	Transparent trimmed PNG via UIPasteboard	Trimmed PNG with background via a FileProvider URI
trim margin	2 pt	0.6 × penMaxWidth dp + 2 px
SVG units and widths	Points, average width per stroke	Physical pixels, (penMinWidth + penMaxWidth) / 2
toFile location	Temporary directory	Cache directory
saveToPhotoLibrary result	{ granted }; granted: false when access is denied	{ granted, uri }; granted: false when the write fails

Details are on Export formats.

Stroke data

	iOS	Android
Coordinates	Points	dp
t	Seconds since the stroke started	Milliseconds of system uptime
Extra fields	pressure, size, azimuth, altitude	None
Restored width	Per-point size	Current penMinWidth and penMaxWidth

See Stroke data and replay.

Input

	iOS	Android
pencilOnly	PencilKit drawingPolicy (iOS 14+). Fingers are ignored.	Only TOOL_TYPE_STYLUS draws. Fingers and the stylus eraser end are ignored.
Inside a ScrollView	No extra handling	The view asks its parents not to intercept the touch once a stroke starts
Pressure	Used by PencilKit	Not used; width comes from speed only
showToolPicker	Shows the PencilKit tool picker	Ignored

Toolbar

	iOS	Android
Icons	SF Symbols	Bundled vector drawables in the same style
Overflow menu	Native menu with icons (iOS 14+), action sheet on older versions	PopupMenu with labels only

Events

	iOS	Android
onChange per stroke	Can fire more than once	Once
onChange vs onEnd order	onEnd first	onChange first
Render error message	Failed to encode image	Failed to render bitmap