Avoid rounding error in image rotation

* src/image.c (image_set_rotation): Halve translations as double values.

diff --git a/src/image.c b/src/image.c
index a3747cfa6b75b4647b788ef641a375e7ce62f1ad..c08b898e7d8da959aeed5bc4151b7083f8dd8b3a 100644 (file)
--- a/src/image.c
+++ b/src/image.c
@@ -2139,7 +2139,7 @@ image_set_rotation (struct image *img, matrix3x3 tm)
   matrix3x3 t
     = { [0][0] = 1,
                                  [1][1] = 1,
-       [2][0] = img->width >> 1, [2][1] = img->height >> 1, [2][2] = 1 };
+       [2][0] = img->width * .5, [2][1] = img->height * .5, [2][2] = 1 };
   matrix3x3 tmp;
   matrix3x3_mult (t, tm, tmp);
 
@@ -2151,8 +2151,8 @@ image_set_rotation (struct image *img, matrix3x3 tm)
   matrix3x3_mult (rot, tmp, tmp2);
 
   /* Translate back.  */
-  t[2][0] = - (width >> 1);
-  t[2][1] = - (height >> 1);
+  t[2][0] = - (width * .5);
+  t[2][1] = - (height * .5);
   matrix3x3_mult (t, tmp2, tm);
 
   img->width = width;