Detect JXL image data on a readable/seekable SDL_RWops.
int IMG_isJXL(SDL_RWops *src);
a seekable/readable SDL_RWops to provide image data.
Returns non-zero if this is JXL data, zero otherwise.
This function attempts to determine if a file is a given filetype, reading the least amount possible from the SDL_RWops (usually a few bytes).
There is no distinction made between "not the filetype in question" and basic i/o errors.
This function will always attempt to seek the RWops back to where it started when this function was called, but it will not report any errors in doing so, but assuming seeking works, this means you can immediately use this with a different IMG_isTYPE function, or load the image without further seeking.
You do not need to call this function to load data; SDL_image can work to determine file type in many cases in its standard load functions.
This function is available since SDL_image 2.6.0.