# rowStride The width, in pixels, of the underlying memory, including any additional row byte padding. ``` var rowStride: Int { get } ``` ## Discussion Use this property when working with the [`AccelerateBuffer`](/documentation/Accelerate/AccelerateBuffer) and [`AccelerateMutableBuffer`](/documentation/Accelerate/AccelerateMutableBuffer) functions. The property allows you to limit work you do on the underlying memory of a pixel buffer to just the visible pixels. In some cases, vImage adds extra bytes at the end of each row. Use [`rowStride`](/documentation/Accelerate/vImage/PixelBuffer/rowStride) to find the width, in pixels, of the memory pointed to by the vImage buffer’s [`data`](/documentation/Accelerate/vImage_Buffer/data) property. For example, the following code creates a 5 x 1 [`vImage.InterleavedFx2`](/documentation/Accelerate/vImage/InterleavedFx2) buffer that contains the pixel values `(1, 2)`, `(3, 4)`, `(5, 6)`, `(7, 8)`, and `(9, 10)`: ```swift let values: [Float] = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] let buffer = vImage.PixelBuffer(pixelValues: values, size: vImage.Size(width: 5, height: 1), pixelFormat: vImage.InterleavedFx2.self) ``` In this case, the [`rowStride`](/documentation/Accelerate/vImage/PixelBuffer/rowStride) is `8`. This equates to the buffer’s [`rowBytes`](/documentation/Accelerate/vImage_Buffer/rowBytes) property of `64`. Each pixel contains two 32-bit values, which is equivalent to 8 bytes per pixel, and 8 bytes per pixel multiplied by the [`rowStride`](/documentation/Accelerate/vImage/PixelBuffer/rowStride) of 8 pixels equals 64. ### Working with the underlying row-bytes property. If you’re accessing the underlying bytes of a pixel buffer, note that the [`rowStride`](/documentation/Accelerate/vImage/PixelBuffer/rowStride) `*` [`channelCount`](/documentation/Accelerate/vImage/PixelBuffer/channelCount) `*` [`bitCountPerPixel`](/documentation/Accelerate/StaticPixelFormat/bitCountPerPixel) may not correspond to the [`rowBytes`](/documentation/Accelerate/vImage_Buffer/rowBytes) properly of the underlying [`vImage_Buffer`](/documentation/Accelerate/vImage_Buffer). This may happen when the integer row stride multiplied by the number of bytes per pixel isn’t a factor of the row bytes. In this case, use the [`withUnsafeVImageBuffer(_:)`](/documentation/Accelerate/vImage/PixelBuffer/withUnsafeVImageBuffer(_:)) function to access the underlying vImage buffer. For example, the following code creates a 3-channel, 8-bit-per-channel 5 x 5 pixel buffer. The code uses the [`rowStride`](/documentation/Accelerate/vImage/PixelBuffer/rowStride) property to fill the buffer with the constant value `99`. The pixel buffer’s underlying bytes per row is `16`, but because the [`rowStride`](/documentation/Accelerate/vImage/PixelBuffer/rowStride) property returns `5`, the code calculates `5 * 3` or `15` bytes per row. Although the code correctly calculates the `5 * 5 * 3` elements, it doesn’t consider the row padding. ```swift let width = 5 let height = 5 let pixelBuffer = vImage.PixelBuffer(size: .init(width: width, height: height), pixelFormat: vImage.Interleaved8x3.self) pixelBuffer.withUnsafeMutableBufferPointer { buf in // The following calculation for `n` doesn't properly consider the row // padding and fails to fill all the elements in `buf`. let n = pixelBuffer.rowStride * pixelBuffer.channelCount * pixelBuffer.height for i in 0 ..< n { buf[i] = 99 } } ``` After the loop completes, the last four elements of the pixel buffer’s [`array`](/documentation/Accelerate/vImage/PixelBuffer/array) are `0`. For more information on how the vImage library adds additional padding to a buffer’s memory, see [`vImage_Buffer`](/documentation/Accelerate/vImage_Buffer). The code below performs a similar loop to that above, but uses the [`rowBytes`](/documentation/Accelerate/vImage_Buffer/rowBytes) property to determine the length of the loop. In this case, the code successfully fills the entire buffer with the value `99`. ```swift pixelBuffer.withUnsafeVImageBuffer { // The following calculation for `n` properly considers the row // padding and fills all the elements in `buf`. let n = $0.rowBytes * Int($0.height) let buf = UnsafeMutableBufferPointer( start: $0.data.assumingMemoryBound(to: Pixel_8.self), count: n ) for i in 0 ..< buf.count { buf[i] = 99 } } ``` --- 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)