Fix particles mode

It was broken after previous commit

Author: fsobolev

src/draw_functions.py

@@ -208,9 +208,9 @@ def levels(sample, cr, width, height, colors, offset, radius):
     for i in range(ls):
         q = int(round(sample[i], 1) * 10)
         for r in range(q):
-            draw_element(cr, step * i + step * offset / 100, \
-                height - (height / 10 * (r + 1)) * (1 - offset / 400), \
-                max(step - step * offset / 100 * 2, 1), \
+            draw_element(cr, step * (i + 0.5), \
+                height - (height / 10 * (r + 0.5)), \
+                max(step - step * offset / 50, 1), \
                 max(height / 10 * (1 - offset / 50), 1), radius)
     cr.fill()