# CGGetDisplaysWithOpenGLDisplayMask(_:_:_:_:) Provides a list of displays that corresponds to the bits set in an OpenGL display mask. ``` func CGGetDisplaysWithOpenGLDisplayMask(_ mask: CGOpenGLDisplayMask, _ maxDisplays: UInt32, _ displays: UnsafeMutablePointer?, _ matchingDisplayCount: UnsafeMutablePointer?) -> CGError ``` ## Parameters `mask` An OpenGL display mask that identifies one or more displays. `maxDisplays` The size of the `displays` array. This value determines the maximum number of displays the list includes. `displays` A pointer to storage you provide for an array of display IDs. On return, the array contains a list of displays that corresponds to the bits set in the mask. If you pass `NULL`, on return the display count contains the total number of displays specified in the mask. `matchingDisplayCount` A pointer to a display count variable you provide. On return, the display count contains the actual number of displays the function added to the `displays` array. This value is at most `maxDisplays`. ## Return Value A result code. To interpret the result code, see [`CGError`](/documentation/CoreGraphics/CGError). ## Discussion --- 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)