aboutsummaryrefslogtreecommitdiff
path: root/fastiv-io.c
diff options
context:
space:
mode:
Diffstat (limited to 'fastiv-io.c')
-rw-r--r--fastiv-io.c46
1 files changed, 46 insertions, 0 deletions
diff --git a/fastiv-io.c b/fastiv-io.c
index f76e817..c16c61d 100644
--- a/fastiv-io.c
+++ b/fastiv-io.c
@@ -1123,6 +1123,52 @@ fastiv_io_open_from_data(const char *data, size_t len, const gchar *path,
return surface;
}
+// --- Metadata ----------------------------------------------------------------
+
+FastivIoOrientation
+fastiv_io_exif_orientation(const guint8 *tiff, gsize len)
+{
+ // libtiff also knows how to do this, but it's not a lot of code.
+ // The "Orientation" tag/field is part of Baseline TIFF 6.0 (1992),
+ // it just so happens that Exif is derived from this format.
+ // There is no other meaningful placement for this than right in IFD0,
+ // describing the main image.
+ const uint8_t *end = tiff + len,
+ le[4] = {'I', 'I', 42, 0},
+ be[4] = {'M', 'M', 0, 42};
+
+ uint16_t (*u16)(const uint8_t *) = NULL;
+ uint32_t (*u32)(const uint8_t *) = NULL;
+ if (tiff + 8 > end) {
+ return FastivIoOrientationUnknown;
+ } else if (!memcmp(tiff, le, sizeof le)) {
+ u16 = wuffs_base__peek_u16le__no_bounds_check;
+ u32 = wuffs_base__peek_u32le__no_bounds_check;
+ } else if (!memcmp(tiff, be, sizeof be)) {
+ u16 = wuffs_base__peek_u16be__no_bounds_check;
+ u32 = wuffs_base__peek_u32be__no_bounds_check;
+ } else {
+ return FastivIoOrientationUnknown;
+ }
+
+ const uint8_t *ifd0 = tiff + u32(tiff + 4);
+ if (ifd0 + 2 > end)
+ return FastivIoOrientationUnknown;
+
+ uint16_t fields = u16(ifd0);
+ enum { BYTE = 1, ASCII, SHORT, LONG, RATIONAL,
+ SBYTE, UNDEFINED, SSHORT, SLONG, SRATIONAL, FLOAT, DOUBLE };
+ enum { Orientation = 274 };
+ for (const guint8 *p = ifd0 + 2; fields-- && p + 12 <= end; p += 12) {
+ uint16_t tag = u16(p), type = u16(p + 2);
+ uint32_t count = u32(p + 4), value = u32(p + 8);
+ if (tag == Orientation && type == SHORT && count == 1 &&
+ value >= 1 && value <= 8)
+ return value;
+ }
+ return FastivIoOrientationUnknown;
+}
+
// --- Thumbnails --------------------------------------------------------------
GType