Creates a thumbnail image for the specified file.
- macOS 10.5+
The allocator to use to create the thumbnail image.
The URL locating the file to create a thumbnail image for.
The maximum desired size of the thumbnail image.
Returns the thumbnail image or
NULL if Quick Look does not support this file type
This function does not supplant the use of Icon Services by applications as a way to get generic file icons and custom icons stored in the metadata fork of files.
Thread-safety: This function is thread-safe so you can call it from any thread. However, because it is synchronous, you should generally call it in a background thread.