Disable --auto-rotate in feh builds compiled wiht Imlib2 1.7.5+

Imlib2 v1.7.5 introduces automatic (and transparent) orientation adjustment
based on EXIF orientation tags. This makes feh's --auto-rotate function
both superfluous and erroneous: It doesn't know about Imlib2's adjustments,
so it rotates an image which is already correctly oriented, leading to
incorrect orientation.

I am not aware of a simple run-time check for detecting whethen running
Imlib2 < 1.7.5 or ≥ 1.7.5. For now, feh disables --auto-rotate entirely when
compiled on a system with Imlib2 1.7.5+ and outputs a warning when the
option is used.

Rationale: The Imlib2 version available at run-time should in most cases be
at least as recent as the Imlib2 version used at compile-time. So, while there
may be cases where feh was compiled with Imlib2 1.7.4 and exhibits erroneous
auto-rotate behaviour on an Imlib2 1.7.5 system, the inverse case
(a feh with disabled auto-rotate support running on Imlib2 1.7.4) should be
sufficiently rare. If it does occur, it can be remedied by compiling feh
from source locally.

Possible caveat: Imlib2 only adjusts for EXIF orientation when loading JPEG
and TIFF images. If there are additional EXIF-aware file formats supported by
feh, but not Imlib2, they lose auto-rotate support.

Reference: GitHub issue #642

3 files changed, 10 insertions, 1 deletions

diff --git a/man/feh.pre b/man/feh.pre
index d495254..340d6cd 100644
--- a/man/feh.pre
+++ b/man/feh.pre
@@ -261,9 +261,12 @@ Automatic reload is not supported in montage, index, or thumbnail mode.
 .It Cm --auto-rotate
 .
 .Pq optional feature, $MAN_EXIF$ in this build
+.Pq deprecated in favor of Imlib2's auto-orientation support
 Automatically rotate images based on EXIF data.
 Does not alter the image files.
 .
+.Pp
+.
 Note that Imlib2 version 1.7.5+ performs auto-rotation by itself, so this option is obsolete on systems with Imlib2 version 1.7.5 or later.
 .Nm
 currently cannot detect this at runtime.
diff --git a/src/imlib.c b/src/imlib.c
index add88d6..c42c4a4 100644
--- a/src/imlib.c
+++ b/src/imlib.c
@@ -462,8 +462,9 @@ int feh_load_image(Imlib_Image * im, feh_file * file)
 	if (file->ed) {
 		ExifByteOrder byteOrder = exif_data_get_byte_order(file->ed);
 		ExifEntry *exifEntry = exif_data_get_entry(file->ed, EXIF_TAG_ORIENTATION);
-		if (exifEntry && opt.auto_rotate)
+		if (exifEntry && opt.auto_rotate) {
 			orientation = exif_get_short(exifEntry->data, byteOrder);
+		}
 	}
 
 	if (orientation == 2)
diff --git a/src/options.c b/src/options.c
index 4d1e527..71c65e2 100644
--- a/src/options.c
+++ b/src/options.c
@@ -758,7 +758,12 @@ static void feh_parse_option_array(int argc, char **argv, int finalrun)
 			opt.draw_exif = 1;
 			break;
 		case OPTION_auto_rotate:
+#if defined(IMLIB2_VERSION_MAJOR) && defined(IMLIB2_VERSION_MINOR) && defined(IMLIB2_VERSION_MICRO) && (IMLIB2_VERSION_MAJOR > 1 || IMLIB2_VERSION_MINOR > 7 || IMLIB2_VERSION_MICRO >= 5)
+			weprintf("This feh release was built with Imlib2 version %d.%d.%d, which transparently adjusts for image orientation according to EXIF data.", IMLIB2_VERSION_MAJOR, IMLIB2_VERSION_MINOR, IMLIB2_VERSION_MICRO);
+			weprintf("--auto-rotate would rotate an already correctly oriented image, resulting in incorrect orientation. It has been disabled in this build. Rebuild feh with Imlib2 <1.7.5 to enable --auto-rotate.");
+#else
 			opt.auto_rotate = 1;
+#endif
 			break;
 #endif
 		case OPTION_no_xinerama: