Magnifier

Magnifier shows a floating loupe over the screen so the user can see a zoomed copy of content under their finger. It is the same interaction Android uses when text becomes hard to read while selecting or dragging.

In Droid, Magnifier is a live object wrapper. It is not a view you drop into a layout builder. You receive an existing android.widget.Magnifier from Android, then show, move, zoom, and dismiss that loupe from Swift.

Because the loupe is a temporary overlay, treat it as interaction chrome rather than permanent UI. It appears near the finger, magnifies a source region, and disappears when the gesture ends.

Use it when…

Use Magnifier when custom drag, selection, or precision controls need a platform-style zoom bubble over the touched content.

Skip it for ordinary zoom buttons or full-screen magnification. Those are better handled with layout scale, a dedicated zoom surface, or accessibility magnification.

How it behaves

show places the loupe over a source point and optionally moves the magnified image to a center point. While it is visible, update() refreshes the captured content and position as the finger moves. dismiss() removes it.

zoom controls magnification. Geometry getters report the current source rectangle, loupe size, position, elevation, and default offsets Android uses when you do not override the center.

content() returns the magnified bitmap when Android has one. originalContent() returns the unzoomed capture. overlay() returns the drawable used as the loupe chrome.

isClippingEnabled() reports whether the source is clipped to the window bounds. setOnOperationCompleteCallback attaches an Android callback object for show/update/dismiss completion events.

Examples

Show a loupe during a drag

func onDragMove(_ magnifier: Magnifier, x: Float, y: Float) {
    magnifier.show(x, y)
    magnifier.update()
}

The loupe follows the finger and keeps the magnified region in sync.

Pin the magnified image while the source moves

func onPrecisionDrag(_ magnifier: Magnifier, x: Float, y: Float) {
    magnifier.show(x, y, 240, 120)
}

Android samples the source near (x, y) and draws the zoomed image near the requested center.

Finish the gesture cleanly

func onDragEnd(_ magnifier: Magnifier) {
    magnifier.dismiss()
}

func tuneZoom(_ magnifier: Magnifier) {
    magnifier.setZoom(2.5)
}

dismiss() ends the overlay. setZoom(_:) changes magnification before the next show.

Initializers

Magnifier(androidObject)

The initializer accepts an existing JNI object for android.widget.Magnifier. Droid does not construct a magnifier from a view-builder block.

Methods

Show and dismiss

show(_:_:) opens the loupe at source coordinates. show(_:_:_:_:) also places the magnified image at a requested center. update() refreshes content and position. dismiss() closes the loupe.

magnifier.show(x, y)
magnifier.update()
magnifier.dismiss()

Call update() during a continuous gesture so the preview does not freeze.

Zoom

zoom() reads the current magnification. setZoom(_:) changes it and returns the same magnifier for chaining.

let current = magnifier.zoom()
magnifier.setZoom(3.0)

Geometry

sourceWidth(), sourceHeight(), and sourcePosition() describe the sampled region. width(), height(), and position() describe the loupe itself. cornerRadius() and elevation() report the chrome styling Android applies.

let source = magnifier.sourcePosition()
let loupeSize = magnifier.width()

defaultHorizontalSourceToMagnifierOffset() and defaultVerticalSourceToMagnifierOffset() return the offsets Android uses when the loupe center is not overridden.

Content and overlay

content() returns the magnified bitmap when available. originalContent() returns the pre-zoom capture. overlay() returns the drawable used as loupe background.

if let bitmap = magnifier.content() {
    // inspect the magnified frame
}

magnifierDefaultSize() returns Android’s default loupe size. Both instance and class forms are available.

Clipping and callbacks

isClippingEnabled() reports whether source sampling is clipped. setOnOperationCompleteCallback(_:) attaches a JNI-compatible callback object for operation completion.

magnifier.setOnOperationCompleteCallback(callback)

The callback must already be an Android-compatible listener object.

Notes

The loupe is gesture chrome. Create or obtain the native Magnifier through the Android API that owns the interaction, then drive it with these methods for the lifetime of the gesture.