If you could include some documentation in the topic for TIEFileFormatInfo.ReadFunction, that would be a big help.
Specifics: 1. What does Preview parameter mean. Based on debugging, it seems like if someone only wants to load the IOParamVals, Preview is true. That is not very obvious. Am I missing another useage of it?
2. How to signal that the load failed. Based on traversing your source code, it seems I have TProgressRec.Aborting^:=True since you stick a pointer to the TImageEnIO Aborting field in the TProgressRec. What benefit do you get by this unobvious approach, aside from confusing users? Having a var ImageLoadedOk:boolean parameter, or 3 lines of documentation would have saved me quite a bit of time.
I will improve the help documentation for the next release.
1. When Preview is true, ImageEn is only seeking to fill IOParams, not load the image (i.e. you can skip filling of Bitmap as it will be ignored. It has no other purpose.
2. Yes, that is correct. Set Progress.Aborting^ := True ;