Struct VNTrackingRequest

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#[repr(C)]
pub struct VNTrackingRequest { /* private fields */ }

Available on crate features VNRequest and VNTrackingRequest only.

Expand description

A base class for all tracking requests.

Since this class is not meant to be directly instantiated, no initializers are available.

Implementations§

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impl VNTrackingRequest

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pub unsafe fn inputObservation(&self) -> Retained<VNDetectedObjectObservation>

Available on crate feature VNObservation only.

The observation object that defines a region to track. Providing an observation not returned from a tracker (e.g. user-defined, or from a detector) begins a new tracker for the sequence. Providing an observation that was returned from a tracker continues the use of that tracker, to track the region to the next frame. In general, unless documented in the request’s documentation, the rectangle must be defined in normalized coordinates (both dimensions normalized to [0,1] with the origin at the lower-left corner).

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pub unsafe fn setInputObservation( &self, input_observation: &VNDetectedObjectObservation, )

Available on crate feature VNObservation only.

Setter for inputObservation.

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pub unsafe fn trackingLevel(&self) -> VNRequestTrackingLevel

Tracking level allows tuning tracking algorithm to prefer speed (VNRequestTrackingLevelFast) vs. tracking object location accuracy (VNRequestTrackingLevelAccurate). This property has no effect on general purpose object tracker (VNTrackObjectRequest) revision 2 (VNTrackObjectRequestRevision2)

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pub unsafe fn setTrackingLevel(&self, tracking_level: VNRequestTrackingLevel)

Setter for trackingLevel.

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pub unsafe fn isLastFrame(&self) -> bool

This property allows marking the last frame for tracking using current tracker. If set to YES, the results for this frame will be processed and returned and the current tracker will be released to the pool of available trackers

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pub unsafe fn setLastFrame(&self, last_frame: bool)

Setter for isLastFrame.

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pub unsafe fn init(this: Allocated<Self>) -> Retained<Self>

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pub unsafe fn initWithCompletionHandler( this: Allocated<Self>, completion_handler: VNRequestCompletionHandler, ) -> Retained<Self>

Available on crate feature block2 only.

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impl VNTrackingRequest

Methods declared on superclass NSObject.

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pub unsafe fn new() -> Retained<Self>

Methods from Deref<Target = VNImageBasedRequest>§

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pub unsafe fn regionOfInterest(&self) -> CGRect

Available on crate feature objc2-core-foundation only.

The region of the image in which the request will be performed. The rectangle is normalized to the dimensions of the image being processed and has its origin specified relative to the image’s lower-left corner.

The default value for this property is { { 0, 0 }, { 1, 1 } }. Setting this property to a rectangle that is outside of the normalized coordinate space will be accepted but result in the request failing to be performed.

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pub unsafe fn setRegionOfInterest(&self, region_of_interest: CGRect)

Available on crate feature objc2-core-foundation only.

Setter for regionOfInterest.

Methods from Deref<Target = VNRequest>§

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pub unsafe fn preferBackgroundProcessing(&self) -> bool

A hint used to minimize the resource burden of the request. Memory footprint, processing footprint and/or CPU/GPU contention will be reduced (depending on the request), at the potential cost of longer execution time. This can help, for example, with ensuring UI updates and rendering are not getting blocked by Vision processing.

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pub unsafe fn setPreferBackgroundProcessing( &self, prefer_background_processing: bool, )

Setter for preferBackgroundProcessing.

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pub unsafe fn usesCPUOnly(&self) -> bool

👎Deprecated

This property, if set to YES, signifies that the request should be performed exclusively on the CPU and not on the GPU. The default value is NO, which signifies that the request is free to leverage the GPU to accelerate any work the request may require.

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pub unsafe fn setUsesCPUOnly(&self, uses_cpu_only: bool)

👎Deprecated

Setter for usesCPUOnly.

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pub unsafe fn results(&self) -> Option<Retained<NSArray<VNObservation>>>

Available on crate feature VNObservation only.

The collection of VNObservations generated by the processing of the request.

The only valid time to access this property is after the request has been processed by a request handler. If the request failed, this property will be nil; otherwise, it will be an array of zero or more VNObservation subclasses specific to the VNRequest subclass.

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pub unsafe fn completionHandler(&self) -> VNRequestCompletionHandler

Available on crate feature block2 only.

The completion handler block that will be invoked after the request has completed processing.

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pub unsafe fn revision(&self) -> NSUInteger

The specific algorithm or implementation revision that is to be used to perform the request.

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pub unsafe fn setRevision(&self, revision: NSUInteger)

Setter for revision.

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pub unsafe fn cancel(&self)

Tries to abort the request as soon as possible. Results will be nil. The completionHandler (if present) will be called with an error of VNErrorRequestCancelled.

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pub unsafe fn supportedComputeStageDevicesAndReturnError( &self, ) -> Result<Retained<NSDictionary<VNComputeStage, NSArray<ProtocolObject<dyn MLComputeDeviceProtocol>>>>, Retained<NSError>>

Available on crate features VNTypes and objc2-core-ml only.

Obtain the collection of compute device per stage that are supported by the request.

This method’s result is based on the current state of configuration of the target request at the time of the call.

Parameter error: The address of a variable that will be populated with the error that describes the failure. If the caller does not require this information, NULL can be passed.

Returns: A dictionary of per-stage supported compute devices, or nil if an error occurs.

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pub unsafe fn computeDeviceForComputeStage( &self, compute_stage: &VNComputeStage, ) -> Option<Retained<ProtocolObject<dyn MLComputeDeviceProtocol>>>

Available on crate features VNTypes and objc2-core-ml only.

Determine what the currently configured compute device is for a specific compute stage.

Parameter computeStage: The compute stage to be introspected.

Returns: The currently assigned compute device, or nil if there is no explicit assignment.

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pub unsafe fn setComputeDevice_forComputeStage( &self, compute_device: Option<&ProtocolObject<dyn MLComputeDeviceProtocol>>, compute_stage: &VNComputeStage, )

Available on crate features VNTypes and objc2-core-ml only.

Assign a specific compute device for a compute stage.

It is important to note that any compute device can be configured for a given compute stage. Only when the request is performed is the validity of the (compute device / compute stage) assignments checked. Valid compute devices for a request’s compute stages can be obtained via -supportedComputeStageDevicesAndReturnError:.

Parameter computeDevice: The compute device to assign to the compute stage. Passing nil for this parameter will remove any explicit compute device assignment, allowing Vision to select which device to use.

Parameter computeStage: The compute stage being configured.

Methods from Deref<Target = NSObject>§

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pub fn doesNotRecognizeSelector(&self, sel: Sel) -> !

Handle messages the object doesn’t recognize.

See Apple’s documentation for details.

Methods from Deref<Target = AnyObject>§

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pub fn class(&self) -> &'static AnyClass

Dynamically find the class of this object.

§Panics

May panic if the object is invalid (which may be the case for objects returned from unavailable init/new methods).

§Example

Check that an instance of NSObject has the precise class NSObject.

use objc2::ClassType;
use objc2::runtime::NSObject;

let obj = NSObject::new();
assert_eq!(obj.class(), NSObject::class());

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pub unsafe fn get_ivar<T>(&self, name: &str) -> &T
where T: Encode,

👎Deprecated: this is difficult to use correctly, use Ivar::load instead.

Use Ivar::load instead.

§Safety

The object must have an instance variable with the given name, and it must be of type T.

See Ivar::load_ptr for details surrounding this.

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pub fn downcast_ref<T>(&self) -> Option<&T>
where T: DowncastTarget,

Attempt to downcast the object to a class of type T.

This is the reference-variant. Use Retained::downcast if you want to convert a retained object to another type.

§Mutable classes

Some classes have immutable and mutable variants, such as NSString and NSMutableString.

When some Objective-C API signature says it gives you an immutable class, it generally expects you to not mutate that, even though it may technically be mutable “under the hood”.

So using this method to convert a NSString to a NSMutableString, while not unsound, is generally frowned upon unless you created the string yourself, or the API explicitly documents the string to be mutable.

See Apple’s documentation on mutability and on isKindOfClass: for more details.

§Generic classes

Objective-C generics are called “lightweight generics”, and that’s because they aren’t exposed in the runtime. This makes it impossible to safely downcast to generic collections, so this is disallowed by this method.

You can, however, safely downcast to generic collections where all the type-parameters are AnyObject.

§Panics

This works internally by calling isKindOfClass:. That means that the object must have the instance method of that name, and an exception will be thrown (if CoreFoundation is linked) or the process will abort if that is not the case. In the vast majority of cases, you don’t need to worry about this, since both root objects NSObject and NSProxy implement this method.

§Examples

Cast an NSString back and forth from NSObject.

use objc2::rc::Retained;
use objc2_foundation::{NSObject, NSString};

let obj: Retained<NSObject> = NSString::new().into_super();
let string = obj.downcast_ref::<NSString>().unwrap();
// Or with `downcast`, if we do not need the object afterwards
let string = obj.downcast::<NSString>().unwrap();

Try (and fail) to cast an NSObject to an NSString.

use objc2_foundation::{NSObject, NSString};

let obj = NSObject::new();
assert!(obj.downcast_ref::<NSString>().is_none());

Try to cast to an array of strings.

use objc2_foundation::{NSArray, NSObject, NSString};

let arr = NSArray::from_retained_slice(&[NSObject::new()]);
// This is invalid and doesn't type check.
let arr = arr.downcast_ref::<NSArray<NSString>>();

This fails to compile, since it would require enumerating over the array to ensure that each element is of the desired type, which is a performance pitfall.

Downcast when processing each element instead.

use objc2_foundation::{NSArray, NSObject, NSString};

let arr = NSArray::from_retained_slice(&[NSObject::new()]);

for elem in arr {
    if let Some(data) = elem.downcast_ref::<NSString>() {
        // handle `data`
    }
}