[Qt-interest] real time strip chart

[Jason H]

Don't EEGs and the like use a simple modulus X position update? That is, 
Starting with 00000:
10000
12000
12300
12340
12345
62345
67345...
This simple modulus means you only need to erase and set one pixel or memory 
value at a time. This is why it has been used for so long. (Plus, it works well 
with a CRT)

Unfortunately, if you are not hardware accelerated, scrolling a window could 
take a decent amount of CPU. You might be better off erasing all data points (1 
pixel per x) and writing the new one. This would be like erasing your line - 
just the line, and plotting a new one. If you can store each value as a discrete 
pixel (no zoom) this should work well. If you have to draw lines, then you will 
use a lot more CPU. It is shocking the amount of processor a line takes on a 
CPU/GPU. If you need zoom, you could store a couple lines corresponding to 
discrete zoom values.






________________________________
From: Atlant Schmidt <aschmidt at dekaresearch.com>
To: Syam Krishnan <syamcr at gmail.com>; "qt-interest at qt.nokia.com" 
<qt-interest at qt.nokia.com>
Sent: Mon, May 23, 2011 6:35:36 AM
Subject: Re: [Qt-interest] real time strip chart

 
Syam:
 
  That, unfortunately, is the difference between a truly high-quality
  interface and one that is perceived by its developer as being
  “good enough” but perceived by everyone else (including the
  customers) as “shoddy”.
 
  Turning again to my Nokia example, Nokia perceived S60 as
  being “good enough”. And so it was until Apple showed the
  world what a truly high-quality interface looked like. Then, the
  rest of the world started seeing S60 as just being “shoddy”.

  5 or 10 FPS would look positively lousy on a strip chart that’s
  moving at 5 cm/second. That’s jumps of 10 or 5 mm! Do you
  think *ANYONE* would think that was smooth animation?
 
                                        Atlant
 

________________________________
 
From:qt-interest-bounces+aschmidt=dekaresearch.com at qt.nokia.com 
[mailto:qt-interest-bounces+aschmidt=dekaresearch.com at qt.nokia.com] On Behalf Of 
Syam Krishnan
Sent: Saturday, May 21, 2011 07:47
To: qt-interest at qt.nokia.com
Subject: Re: [Qt-interest] real time strip chart
 
On 05/20/2011 09:36 PM, giovanni drogo wrote: 
Hi All,
I'm developing a QT application which includes a real  time chart (with several 
(8 or more) traces), similar to an ECG monitor. Traces should move on the 
monitor with a speed of about 5cm/sec. 

Well, how 'frequently' do you really need your plot to be updated? Once in 100ms 
or 200ms (i.e. 10 fps or 5fps) is enough?
If that's the case, then you can use Qwt (QwtPlot class). I am using it and it 
works quite fine. You might need to do some manual management
of data arrays for efficiency though.


regards,

Syam


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