After some testing of the behaviour of this stuff, it became clear that the current
pressure handling here isn't very useful. The initial point would invariably get a
low pressure value (due to the way that the initial tap needs time to "take"), while
the end of the stroke suffers from similar issues (i.e. when the pen is released).
Meanwhile, the line thickness would flicker while drawing the stroke, as the endpoint
pressure varied.
So, until we find a better way, all straight line segments are now drawn without
pressure sensitivity.
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