diff options
| -rw-r--r-- | fastiv-io.c | 46 | ||||
| -rw-r--r-- | fastiv-io.h | 17 |
2 files changed, 63 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 diff --git a/fastiv-io.h b/fastiv-io.h index 3aed342..a611078 100644 --- a/fastiv-io.h +++ b/fastiv-io.h @@ -46,6 +46,23 @@ cairo_surface_t *fastiv_io_open_from_data( int fastiv_io_filecmp(GFile *f1, GFile *f2); +// --- Metadata ---------------------------------------------------------------- + +// https://www.cipa.jp/std/documents/e/DC-008-2012_E.pdf Table 6 +typedef enum _FastivIoOrientation { + FastivIoOrientationUnknown = 0, + FastivIoOrientation0 = 1, + FastivIoOrientationMirror0 = 2, + FastivIoOrientation180 = 3, + FastivIoOrientationMirror180 = 4, + FastivIoOrientationMirror90 = 5, + FastivIoOrientation90 = 6, + FastivIoOrientationMirror270 = 7, + FastivIoOrientation270 = 8 +} FastivIoOrientation; + +FastivIoOrientation fastiv_io_exif_orientation(const guint8 *exif, gsize len); + // --- Thumbnails -------------------------------------------------------------- // And this is how you avoid glib-mkenums. |