#146 Issues in current rotated-image support
Wanting to investigate some issues with page/image rotation in the wake of #144, I put myself together a little test-file generator. It's a set of SVG files and a zsh script (specifically, since I use several zshisms) that will turn those SVG files into a PNG- or JPG-format .cbr comic containing a series of pages in various orientations, both real and metadata-defined.
Basically, the way it works is that all 10 pages of the "comic" are spun around in all different directions, but with metadata that should cause the big, red arrow to be pointing upwards in the final rendering.
Using those test files, I discovered two things about MComix's page-rotation support.
1. While JPEG-format pages are rotated properly, their thumbnails are not
The JPEG pages of the test file all showed with the red arrow pointing upwards, as expected. However, their thumbnails are all over the place, as you can see in the attached screenshot.
2. PNG files are not rotated at all, if their rotation is defined in EXIF data
PNG files actually gained support for EXIF data in 2017, via a new eXIf chunk. Many tools today will use that, in preference to storing metadata in legacy tEXt data chunks. When I created my test .cbr files via the script I mentioned, I used exiftool to set the page orientations, regardless of file type. exiftool has been updated to use the PNG eXIf chunk.
Unfortunately, MComix ignores the eXIf data in PNG files, primarily because GDKPixbuf ignores it as well. I've already filed a bug report about that. In the case of the PNG test, the thumbnails were an accurate representation of the file's contents, as the full pages displayed the same as the thumbnails. Again, screenshot attached.
I realized it probably would've made more sense to take those screenshots from some page other than 1, one that's actually rotated. Well, take my word for it. Would I lie? 😇
As I mentioned in a comment on issue #149, this is likely to have changed with the new GdkPixbuf. Its new loader supports PNG EXIF rotation (tested it myself), and my linked bug report above is closed as resolved. So, that should be solved, although MComix may need to be modified to take advantage of the PNG rotation metadata now that it's available.
The issue of not displaying the thumbnails with rotation, though, is probably still MComix's to solve.