Reworked qt terminal is much faster!

[sfeam <sf...@us...>]

Hi all,

I recall from several past threads on the list that some people have been
avoiding the qt terminal because its rendering speed, particularly for
interactive 3D plots, was slower than x11 or wxt.    

Jérôme Lodewyck's recent revisions to the qt driver have changed that 
dramatically.   Here are timing for the execution of "all.dem" under linux
(64-bit, qt5).   I see about the same improvement for 32-bit, qt4.

4.7 all.dem
===========
                  	     user  system   clock
4.7  qt (old)	  4.973u 0.433s 0:24.91 21.6%
4.7 x11		  5.623u 1.364s 0:20.40 34.2%
4.7 wxt		13.845u 1.239s 0:15.58 96.7%
4.7  qt (new)	  4.925u 0.427s 0:07.95 67.1%

The old qt driver indeed had the slowest clock time, behind both x11 and wxt.
The new qt has increased its speed by a factor of 3X on this set of demos
and is now very noticeably the fastest of the the three choices. 

Here is a test of 3D rotation speed (animate.dem modified to use
'set pm3d hidden3d interpolate 3,3')

4.7  qt (old)	0.352u 0.077s 0:05.61 7.4%
4.7 x11      	0.502u 0.328s 0:04.70 17.4%
4.7 wxt        	2.075u 0.308s 0:02.45 96.7%
4.7  qt (new)	0.347u 0.090s 0:01.41 30.4%