RFR: JMC-4613 - Thread name striked out

[Alex Macdonald]

Hi,

The following webrev [0] addresses issue JMC-4613 [1], in which the line
drawn when hovering a thread lane on the Jfr Threads page could intersect
the name label for the thread.

The problem here was the vertical offset for displaying the thread name was
always given the value of 4. However, this could be insufficient for a
number of reasons, the first being that when viewing a few threads 1 to ~4
it didn't offer enough clearance for when the mouse hovers a thread lane -
the bottom of the lane extender clips the name of the thread [2].
Additionally, when there are a lot of threads on the page the labels can be
hard to read because there is no guarantee as to whether or not they will
be displayed in the middle of the row, or at the bottom of the row [3].

To amend this, a new vertical offset value is used in the cases where a
horizontal line is displayed under the thread name. This value if roughly
half the height of the string, and gives enough clearance to not get
intersected [4]. Additionally, when there are no line separators being
drawn the thread names will now be drawn in the middle of the row, which
should make them line up better with their respective lanes [5] and improve
readability when there are many threads on the chart [6].

Lastly, the thread names were previously only printed to the screen if the
height of their row was greater than 20 units. However, there could be
instances where there was enough space to display the names, as seen in the
comparison picture [7].

Thoughts?

Cheers,

Alex

[0] http://cr.openjdk.java.net/~aptmac/JMC-4613/webrev.00/
[1] https://bugs.openjdk.java.net/browse/JMC-4613
[2] https://imgur.com/RGpn4qS
[3] https://imgur.com/RiPEyui
[4] https://imgur.com/6bXzT6g
[5] https://imgur.com/qhFBbNz
[6] https://imgur.com/VByL3zQ
[7] https://imgur.com/JASaq2n