z=dist(100) & z[0, *] = max(z) & z[*, 0] = max(z) & z[*, 99] = max(z) & z[99, *] = max(z)
image= poly_2d(z, [[0,0],[.21,0]], [[0,.21],[0,0]], 0, 480, 480)
Using the latest CVS at this date
With IDL: image framed in white
With GDL: image with top and right borders white, left and bottom black
Comparing the image arrays, it seems that poly2d is the culprit here.