# Diagonal rotation

Sage Cython: To run, type `%attach PicDiagRotate.pyx` and `OK()` at the Sage command line, or paste into a Sage notebook with `%cython` as the first line.

```#PicDiagRotate.pyx
import numpy as np
cimport numpy as np
from scipy import misc
DEF side=512
DEF halfside=side/2
cpdef OK():
cdef int i,w,row,loops,lps,L,R,t
cdef np.ndarray[np.uint8_t, ndim=3] a
fn="tiger-09.png" #a 512x512 colour png
for w in xrange(1,halfside+1):
for row in xrange(w,halfside+1):
#row 1 is the 4 pixels at centre, 256 is around edge of pic.
if row>1: #do twice more for each row outside the first
loops=2
else:
loops=1
for lps in xrange(loops):
L=halfside-row
R=side-1-L
for i in xrange(3): #store temp pixel
t[i]=a[L][L][i]
for i in xrange(L,R,1):	#move left column down
a[L][i]=a[L][i+1]
for i in xrange(L,R): #move top row to the left
a[i][R]=a[i+1][R]
for i in xrange(R,L,-1): #move right column up
a[R][i]=a[R][i-1]
for i in xrange(R,L,-1):#move bottom row to right
a[i][L]=a[i-1][L]
for i in xrange(3): #put temp back
a[L+1][L][i]=t[i]
print w
misc.imsave('tpics/%05d.png' % w,a) #NB make a folder called 'tpics' first.
```