# roiTileArray(forInput:arguments:outputRect:) Override this class method to implement your processor’s tiled ROI callback. ``` class func roiTileArray(forInput inputIndex: Int32, arguments: [String : Any]?, outputRect: CGRect) -> [CIVector] ``` ## Parameters `inputIndex` the index that tells you which processor input for which to return the array of ROI rectangles `arguments` the arguments dictionary that was passed to [`apply(withExtent:inputs:arguments:)`](/documentation/CoreImage/CIImageProcessorKernel/apply(withExtent:inputs:arguments:)). `outputRect` the output `CGRect` that processor will be asked to output. ## Return Value An array of [`CIVector`](/documentation/CoreImage/CIVector) that specify tile regions of the `inputIndex`’th input that is required for the above `outputRect` Each region tile in the array is a created by calling `/CIVector/vectorWithCGRect:` The tiles may overlap but should fully cover the area of ‘input’ that is needed. If a processor has multiple inputs, then each input should return the same number of region tiles. ## Discussion This will be called one or more times per render to determine what tiles of the input images are needed to render a given `outputRect` of the output. If the processor implements this method, then when rendered; - as CoreImage prepares for a render, this method will be called for each input to return an ROI tile array. - as CoreImage performs the render, the method [`process(with:arguments:output:)`](/documentation/CoreImage/CIImageProcessorKernel/process(with:arguments:output:)) will be called once for each tile. > Important: this is a class method so that you cannot use or capture any state by accident. > All the parameters that affect the output results must be passed to > ``doc://com.apple.coreimage/documentation/CoreImage/CIImageProcessorKernel/apply(withExtent:inputs:arguments:)``. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)