Perfect crops.

Also eliminate redundant get_cropspec code.
Also eliminate redundant apply_rotation call.

cropgui_common.py

@@ -69,23 +69,8 @@ def get_cropspec(image, corners, rotation):
     t, l, r, b = corners
     w = r - l
     h = b - t
-
-    # The coordinates passed to jpegtran are interpreted post-rotation.
-    # Non-whole blocks are already imperfectly rotated by being left on the
-    # side, so we need to subtract them
-    if image.format == "JPEG":
-        round_x, round_y = image_round(image)
-        orig_w, orig_h = image.size
-        if rotation in (8, 6):
-            orig_w, orig_h = orig_h, orig_w
-            round_x, round_y = round_y, round_x
-        if rotation in (3, 8):
-            t -= orig_h % round_y
-        if rotation in (3, 6):
-            l -= orig_w % round_x
-        assert t >= 0, "t < 0 should be handled in fix(): {}".format(t)
-        assert l >= 0, "l < 0 should be handled in fix(): {}".format(l)
-
+    # Technically this should produce perfect crops, but jpegtran is broken
+    # and so mistakenly rounds out fractional crops on flipped images.  Sigh.
     return "%dx%d+%d+%d" % (w, h, l, t)
 
 
@@ -209,7 +194,6 @@ class DragManagerBase(object):
 
     def image_or_rotation_changed(self):
         self._image = image = self.apply_rotation(self._orig_image)
-        self.apply_rotation(image)
         self.top, self.bottom = self.fix(0, self.h, self.h, self.round_y, self.rotation in (3, 8))
         self.left, self.right = self.fix(0, self.w, self.w, self.round_x, self.rotation in (3, 6))
         blurred = image.copy()
@@ -227,18 +211,11 @@ class DragManagerBase(object):
         r: rounding size
         reverse: True to treat the upper bound as the origin
         """
-        if reverse:
-            offset = lim % r
-        else:
-            offset = 0
         a, b = sorted((int(a), int(b)))
-        a = ((a - offset) // r) * r + offset
-        b = ((b - offset + r - 1) // r) * r + offset
-        # jpegtran handles non-whole blocks by leaving them on the edge of the
-        # image, away from the rotated position of their old neighbors.
-        # Keeping them isn't useful, so clamp them off.
-        a = clamp(a, offset if reverse else 0, lim)
-        b = clamp(b, offset if reverse else 0, lim)
+        if reverse:
+            a = lim - ((((lim - a) + r - 1) // r) * r)
+        else:
+            a = (a // r) * r
         return a, b
 
     def get_corners(self):