+
+/* Returns a transformation matrix to do rotation as per the provided
+ EXIF "Orientation" value.
+ */
+static CGAffineTransform
+exif_rotate (int rot, CGSize rect)
+{
+ CGAffineTransform trans = CGAffineTransformIdentity;
+ switch (rot) {
+ case 2: // flip horizontal
+ trans = CGAffineTransformMakeTranslation (rect.width, 0);
+ trans = CGAffineTransformScale (trans, -1, 1);
+ break;
+
+ case 3: // rotate 180
+ trans = CGAffineTransformMakeTranslation (rect.width, rect.height);
+ trans = CGAffineTransformRotate (trans, M_PI);
+ break;
+
+ case 4: // flip vertical
+ trans = CGAffineTransformMakeTranslation (0, rect.height);
+ trans = CGAffineTransformScale (trans, 1, -1);
+ break;
+
+ case 5: // transpose (UL-to-LR axis)
+ trans = CGAffineTransformMakeTranslation (rect.height, rect.width);
+ trans = CGAffineTransformScale (trans, -1, 1);
+ trans = CGAffineTransformRotate (trans, 3 * M_PI / 2);
+ break;
+
+ case 6: // rotate 90
+ trans = CGAffineTransformMakeTranslation (0, rect.width);
+ trans = CGAffineTransformRotate (trans, 3 * M_PI / 2);
+ break;
+
+ case 7: // transverse (UR-to-LL axis)
+ trans = CGAffineTransformMakeScale (-1, 1);
+ trans = CGAffineTransformRotate (trans, M_PI / 2);
+ break;
+
+ case 8: // rotate 270
+ trans = CGAffineTransformMakeTranslation (rect.height, 0);
+ trans = CGAffineTransformRotate (trans, M_PI / 2);
+ break;
+
+ default:
+ break;
+ }
+
+ return trans;
+}
+
+