Mantis — Image Cropping Library for iOS (Swift · UIKit · SwiftUI)

Important: set modalPresentationStyle = .fullScreen on the crop view controller (or its navigation controller) when presenting it.

UIKit

let cropViewController = Mantis.cropViewController(image: yourImage)
cropViewController.delegate = self
cropViewController.modalPresentationStyle = .fullScreen
present(cropViewController, animated: true)

The caller conforms to CropViewControllerDelegate:

public protocol CropViewControllerDelegate: AnyObject {
    func cropViewControllerDidCrop(_ cropViewController: CropViewController, cropped: UIImage, transformation: Transformation, cropInfo: CropInfo)
    func cropViewControllerDidCancel(_ cropViewController: CropViewController, original: UIImage)
    
    // The implementation of the following functions are optional
    func cropViewControllerDidFailToCrop(_ cropViewController: CropViewController, original: UIImage)     
    func cropViewControllerDidBeginResize(_ cropViewController: CropViewController)
    func cropViewControllerDidEndResize(_ cropViewController: CropViewController, original: UIImage, cropInfo: CropInfo)    
}

SwiftUI

Declarative API (Mantis 3.0+)

ImageCropper is a declarative SwiftUI view configured with modifiers:

struct MyView: View {
    @State private var croppedImage: UIImage?
var body: some View {         ImageCropper(image: myImage)             .cropShape(.circle)             .aspectRatio(.fixed(16/9))             .onCrop { result in                 croppedImage = result.croppedImage             }     } }

To build your own controls, attach a CropSession. It exposes canUndo, canRedo, isResettable and the live transformation as observable state (fine-grained Observation tracking on iOS 17+, ObservableObject on iOS 15/16), and drives the cropper with plain methods instead of enum bindings:

struct MyCropperView: View {
    @StateObject private var session = CropSession()
    @State private var croppedImage: UIImage?
var body: some View {         VStack {             ImageCropper(image: myImage, session: session)                 .builtInToolbarVisible(false)                 .onCrop { result in croppedImage = result.croppedImage }
HStack {                 Button("Undo") { session.undo() }                     .disabled(!session.canUndo)                 Button("Redo") { session.redo() }                     .disabled(!session.canRedo)                 Button("Reset") { session.reset() }                     .disabled(!session.isResettable)                 Button("Rotate") { session.rotate(.clockwise) }                 Button("Flip") { session.flip(.horizontal) }                 Button("Done") { session.crop() }             }         }     } }

Available modifiers: .cropShape(:), .aspectRatio(:), .builtInToolbarVisible(_:), .appearance(_:), .configure { $0... } (escape hatch to the full Mantis.Config), .onCrop(:), .onCancel(:), .onCropFailed(_:).

Binding-based API

Kept for backward compatibility and fully supported; new code should prefer the declarative ImageCropper above.

struct MyView: View {
    @State private var image: UIImage?
    @State private var transformation: Transformation?
    @State private var cropInfo: CropInfo?
var body: some View {         ImageCropperView(             image: $image,             transformation: $transformation,             cropInfo: $cropInfo         )     } }

Note:

- To start a crop operation programmatically, use the action binding (for ImageCropperView):

>   action = .crop

- To receive the result of the crop (success or failure), use the onCropCompleted callback.

This is especially useful because cropping may not complete instantly in all cases, so relying on this callback ensures you update your UI only after the operation finishes.

CropToolbar has two modes:

• normal mode

let cropViewController = Mantis.cropViewController(image: yourImage)

• embedded mode

var config = Mantis.Config()
config.cropToolbarConfig.mode = .embedded
let cropViewController = Mantis.cropViewController(image: yourImage, config: config)

// Add a custom ratio 1:2 for portrait orientation
var config = Mantis.Config()
config.addCustomRatio(byVerticalWidth: 1, andVerticalHeight: 2)            
let cropViewController = Mantis.cropViewController(image: yourImage, config: config)
// Set the ratioOptions of the config if you don't want to keep all default ratios var config = Mantis.Config()  //config.ratioOptions = [.original, .square, .custom] config.ratioOptions = [.custom] config.addCustomRatio(byVerticalWidth: 1, andVerticalHeight: 2)             let cropViewController = Mantis.cropViewController(image: yourImage, config: config)

• If you always want to use only one fixed ratio, set presetFixedRatioType to alwaysUsingOnePresetFixedRatio:

config.presetFixedRatioType = .alwaysUsingOnePresetFixedRatio(ratio: 16.0 / 9.0)

When choosing alwaysUsingOnePresetFixedRatio, the fixed-ratio setting button does not show. (In the declarative SwiftUI API this is .aspectRatio(.fixed(16/9)).)

• If you want to hide the rotation control view, set config.cropViewConfig.showAttachedRotationControlView = false
• If you want to use a ratio list instead of a presenter, set config.cropToolbarConfig.ratioCandidatesShowType = .alwaysShowRatioList

public enum RatioCandidatesShowType {
    case presentRatioList
    case alwaysShowRatioList
}

• If you build your own custom toolbar you can add your own fixed ratio buttons:

// set a custom fixed ratio
cropToolbarDelegate?.didSelectRatio(ratio: 9 / 16)

To use a different crop shape — for example a circular avatar crop — set config.cropViewConfig.cropShapeType:

public enum CropShapeType {
    case rect
    case square
    case ellipse(maskOnly: Bool = false)
    case circle(maskOnly: Bool = false)
    case roundedRect(radiusToShortSide: CGFloat, maskOnly: Bool = false)
    case diamond(maskOnly: Bool = false)
    case heart(maskOnly: Bool = false)
    case polygon(sides: Int, offset: CGFloat = 0, maskOnly: Bool = false)
    case path(points: [CGPoint], maskOnly: Bool = false)
}

With maskOnly: true, the shape is used only as a visual mask and the exported image stays rectangular; with the default maskOnly: false, the exported image is cut to the shape with a transparent background.

In the declarative SwiftUI API the same type is used: .cropShape(.circle) (the cases whose associated values all have defaults can be written without parentheses).

If you want to apply transformations when showing an image (for example to reopen the editor at a previously saved state), set config.cropViewConfig.presetTransformationType:

public enum PresetTransformationType {
    case none
    case presetInfo(info: Transformation)
    case presetNormalizedInfo(normalizedInfo: CGRect)
}

Please use the transformation information obtained previously from the delegate method cropViewControllerDidCrop(_:cropped:transformation:cropInfo:), or — in the declarative SwiftUI API — from CropResult.transformation delivered by .onCrop.

As of Mantis 3.1.0, CropInfo conforms to Codable, so you can save a user's exact crop and reproduce it offline in a later session — including rotated, fixed-ratio, perspective-skewed, and large-image crops.

// Save the CropInfo delivered by the delegate (or CropResult.cropInfo in SwiftUI).
func cropViewControllerDidCrop(_ cropViewController: CropViewController,
                               cropped: UIImage,
                               transformation: Transformation,
                               cropInfo: CropInfo) {
    let data = try? JSONEncoder().encode(cropInfo)
    // ...persist data (UserDefaults, a file, a database, etc.)
}
// Later — even in a new app session — re-crop the original image offline, no UI: let cropInfo = try JSONDecoder().decode(CropInfo.self, from: data) let recropped = Mantis.crop(image: originalImage, by: cropInfo)

• A decoded CropInfo crops identically to the same-session value: the opaque view-reconstruction state needed by the perspective-skew and maxImagePixelCount (large-image) paths is encoded alongside the public fields.
• Persist a CropInfo that Mantis produced (from the delegate or getCropInfo()). A CropInfo you build by hand via the public init carries no view-reconstruction state, so the perspective and large-image paths still return nil for it — exactly as before.
• If you only need to reopen the editor at the previous state (rather than crop offline), persisting the Transformation and restoring it via presetTransformationType = .presetInfo(info:) remains the lighter option.

Compatibility: adding Codable is purely additive — existing code needs no changes. The one exception: if you previously wrote your own extension CropInfo: Codable as a workaround, remove it after upgrading to avoid a duplicate-conformance error. The encoded JSON mirrors CropInfo's fields, so treat versioning of your own persisted data as your app's responsibility.

• Mantis offers full support for Undo, Redo, and Revert to Original on both iOS and Mac Catalyst.

• To enable this feature, set config.enableUndoRedo = true.

• In the declarative SwiftUI API, attaching a CropSession enables undo/redo automatically and exposes canUndo / canRedo / isResettable as observable state.

• Each crop view controller keeps its own undo history, so multiple croppers can be shown at the same time (Mantis 3.0+).

• Catalyst menus for this feature are localized.

Enable perspective correction to let users adjust horizontal and vertical skew, similar to the Apple Photos app.

var config = Mantis.Config()
config.cropViewConfig.enablePerspectiveCorrection = true
let cropViewController = Mantis.cropViewController(image: yourImage, config: config)

When enablePerspectiveCorrection is true, the slide dial is used by default (no need to set builtInRotationControlViewType explicitly) and automatically switches to withTypeSelector mode, showing three circular icon buttons (Straighten / Vertical / Horizontal) above the ruler. Users can tap each button to switch adjustment modes.

• The skew values are included in the Transformation and CropInfo returned by the delegate, so you can persist and restore them via presetTransformationType.

• You can optionally customize the appearance of the type selector buttons through SlideDialConfig:

Set the appearance mode to control the overall look of the crop UI:

var config = Mantis.Config()
config.appearanceMode = .forceLight   // or .forceDark (default), .system
let cropViewController = Mantis.cropViewController(image: yourImage, config: config)

public enum AppearanceMode {
    /// Always use dark appearance (default, backward compatible)
    case forceDark
    /// Always use light appearance
    case forceLight
    /// Follow system light/dark mode setting
    case system
}

• .forceDark is the default, keeping the existing dark-themed behavior.
• .forceLight uses a light color scheme similar to Apple Photos in light mode.
• .system dynamically adapts to the user's system-wide light/dark mode setting.

Mantis ships with built-in localizations for Arabic, Chinese (Simplified and Traditional), Dutch, English, French, German, Italian, Japanese, Korean, Portuguese, Russian, Spanish, and Turkish.

• UIKit project: add the languages you support to the Localizations section of the Project Info tab.

fig 1

• SwiftUI project: please check this discussion.

• Static frameworks: if you use static frameworks in CocoaPods, you need to add the code below in order to find the correct resource bundle.

Mantis.locateResourceBundle(by: Self.self)

• Custom localization tables and bundle

Important: first create a strings file with these keys:

"Mantis.Done" = "";
"Mantis.Cancel" = "";
"Mantis.Reset" = "";
"Mantis.Original" = "";
"Mantis.Square" = "";
"Mantis.Straighten" = "";
"Mantis.Horizontal" = "";
"Mantis.Vertical" = "";

Then configure Mantis:

let config = Mantis.Config()
config.localizationConfig.bundle = // a bundle where the strings file is located
config.localizationConfig.tableName = // the localized strings file name within the bundle

If needed you can subclass CropViewController:

class CustomViewController: CropViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
// Do your custom logic here.         // The MantisExample project also has a showcase for a CustomViewController.     } }

To get an instance, Mantis provides a factory method:

let cropViewController: CustomViewController = Mantis.cropViewController(image: image, config: config)

These four properties had been deprecated forwarding shims; use the replacements:

| Removed in 3.0 | Use instead | |---|---| | cropViewConfig.cropBoxHotAreaUnit | cropViewConfig.cropAuxiliaryIndicatorConfig.cropBoxHotAreaUnit | | cropViewConfig.disableCropBoxDeformation | cropViewConfig.cropAuxiliaryIndicatorConfig.disableCropBoxDeformation | | cropViewConfig.cropAuxiliaryIndicatorStyle | cropViewConfig.cropAuxiliaryIndicatorConfig.style | | cropViewConfig.showRotationDial | cropViewConfig.showAttachedRotationControlView |

Five view-reconstruction fields (skewSublayerTransform, scrollContentOffset, scrollBoundsSize, imageContainerFrame, scrollViewTransform) moved out of the public struct and its init; they were pure view-hierarchy plumbing for the perspective and large-image crop paths.

• Passing a Mantis-provided CropInfo back into Mantis.crop(image:by:) (from the delegate or getCropInfo()): no change, including across value copies.
• Rebuilding a CropInfo from persisted semantic fields via the public init for offline re-cropping: no change for the standard path. The perspective-skew and maxImagePixelCount overflow paths return nil for a rebuilt CropInfo — the same outcome the previous zero-value guards produced. As of 3.1, prefer persisting the Codable CropInfo Mantis produced — see Persisting and restoring crops.
• Tip: for save-and-restore flows, persist the Transformation and feed it back via presetTransformationType = .presetInfo(info:) — that path is unchanged.

• Undo/redo bookkeeping is now per crop view controller instead of shared globally. If your app shows two croppers at once, each keeps its own undo history (previously they polluted each other's).
• The Mantis.cropViewController(image:config:) factory now correctly wires up undo/redo when config.enableUndoRedo = true; previously only the setupCropViewController path did.

Set modalPresentationStyle = .fullScreen on the crop view controller (or its navigation controller) before presenting it. On iOS 13+ the default sheet presentation style does not work with the crop UI.

Use config.cropViewConfig.cropShapeType = .circle() (UIKit) or .cropShape(.circle) (SwiftUI). The exported UIImage is cut to the circle with a transparent background. If you want the exported image to stay rectangular and only show a circular mask in the UI, use .circle(maskOnly: true).

Two options:

• Re-crop offline (no UI): persist the Codable CropInfo (Mantis 3.1+) and pass it to Mantis.crop(image:by:) later.
• Reopen the editor at the saved state: persist the Transformation and restore it via config.cropViewConfig.presetTransformationType = .presetInfo(info:).

Yes — Mantis supports iOS and Mac Catalyst, including localized Catalyst menus for undo/redo and independent undo histories for multiple croppers (e.g. iPad multi-window).

Set config.cropMode = .async to crop off the main thread, and/or set config.cropViewConfig.maxImagePixelCount to cap the output pixel count for very large photos.