d.frame: round, not truncate, when calculating pixels from percents

Four frames for image size 500x367 were not the same size
with different combinations of 0,49.8,50.2,100 used for at option
to achieve regular 2x2 layout with margins in the middle.


git-svn-id: https://svn.osgeo.org/grass/grass/trunk@69729 15284696-431f-4ddb-bdfa-cd5b030d7da7

scripts/d.frame/d.frame.py

@@ -165,20 +165,42 @@ def print_frames(monitor, current_only=False, full=False):
 def get_frame_name(line):
     return line.rstrip('\n').rsplit('#', 1)[1].strip(' ')
 
-# calculate position of the frame in percent
-
 
 def calculate_frame(frame, at, width, height):
+    """Calculate absolute position of the frame from percentages
+
+    at is from bottom left in percents (bottom,top,left,right)
+    output is in pixels from top left (top,bottom,left,right)
+
+    This function does also the necessary formating.
+
+    >>> calculate_frame('apple', "0,49.8,0,50.2", 500, 500)
+    'GRASS_RENDER_FRAME=251,500,0,251 # apple\\n'
+    >>> calculate_frame('orange', "50.2,0,49.8,100", 500, 500)
+    'GRASS_RENDER_FRAME=500,249,249,500 # orange\\n'
+    >>> calculate_frame('odd_number', "0,49.8,0,50.2", 367, 367)
+    'GRASS_RENDER_FRAME=184,367,0,184 # odd_number\\n'
+
+    The following would give 182,367,0,184 if we would be truncating
+    to integers instead of rounding, but that would be wrong because
+    height of the frame would be 367 minus 182 which is 185 while
+    0.502 times 367 is 184.234 which fits with the (correct) width of
+    the frame which is 184.
+
+    >>> calculate_frame('test_truncating_bug', "0,50.2,0,50.2", 367, 367)
+    'GRASS_RENDER_FRAME=183,367,0,184 # test_truncating_bug\\n'
+    """
     try:
         b, t, l, r = list(map(float, at.split(',')))
     except:
         fatal(_("Invalid frame position: %s") % at)
 
-    top = height - (t / 100. * height)
-    bottom = height - (b / 100. * height)
-    left = l / 100. * width
-    right = r / 100. * width
+    top = round(height - (t / 100. * height))
+    bottom = round(height - (b / 100. * height))
+    left = round(l / 100. * width)
+    right = round(r / 100. * width)
 
+    # %d for floats works like int() - truncates
     return 'GRASS_RENDER_FRAME=%d,%d,%d,%d # %s%s' % \
         (top, bottom, left, right, frame, '\n')
 
@@ -276,5 +298,9 @@ def main():
     select_frame(monitor, options['frame'])
 
 if __name__ == "__main__":
+    if len(sys.argv) == 2 and sys.argv[1] == '--doctest':
+        import doctest
+        _ = str  # doctest gettext workaround
+        sys.exit(doctest.testmod().failed)
     options, flags = parser()
     sys.exit(main())