Independent of whether the grid is on or off, FeynGame will do
additional kinds of clipping when objects are moved by mouse or curved
by mouse wheel:
Vertex clipping. If the end of a line is moved closer to another
line (or to its other end) than a certain minimal distance, it will be
connected with that line through a vertex.
Curvature clipping. If the curvature of a line is decreased below
a certain minimal value via the mouse wheel, it will be set to zero.
Angle clipping. If the slope of a straight line is close to a
multiple of π/2, it will be replaced by that multiple of
&pi/2;. Via the menu item Edit > Clipping angles or by
repeatedly pressing "c", that value can be changed to
π/4 or π16, or zero.
This kind of clipping is introduced for the user's convenience, because
otherwise it would be rather clumsy to connect lines, or to turn a
curved line into a completely straight line. In order to overrule such
clipping, one can use EditFrame to do a pixel-wise modification of the
position or the curvature.