QT4 vs QT2: hardware requirements

[wysota]

Qt4 is of course much more complex than Qt2 but simply measuring the delay between pushing the button and seeing the result doesn't say anything about what is causing the delay. It might be either modifying the palette and all things that happen around it or the process of displaying the changes. Maybe you are using some suboptimal display driver? Try running qws with directfb instead of linuxfb and see if it changes anything.

http://doc.trolltech.com/latest/qt-e...-directfb.html

[Yuri T]

Hi, Wysota!

Thanks for your point, this definitely makes sense. I'll try my application with directfb (I guess, I should at least rebuild QT with the appropriate support for this; and there is no need in a special kernel driver, since the DirectFb lib is based on the standard linux framebuffer driver for my platform), and then post here the results.

P.S. Any other comments on this topic are welcomed as well : ) actually, there are some improvements supposed to be done to this dummy application, e.g. drawing graphics; so it could be very interesting to know about the h/w requirements for different QT libs to make the optimal choice of the h/w platform for the project.

Regards, Yuri

[wysota]

Actually the only hardware requirement for Qt is that the processor supports some atomic operations. The rest is just a matter of how fast or slow will the applications be.

[Yuri T]

It turns out that the following patch to the original code in the start message of this topic fixes the problem of delays:

--- a/main.cpp 2010-05-18 00:16:58.341568500 +0400
+++ b/main.cpp 2010-05-18 00:16:27.147619000 +0400
@@ -1,4 +1,5 @@
#include <QApplication>
+#include <QStyleFactory>

#include "ui_but.h"
#include "main.h"
@@ -115,6 +116,8 @@ MyWidget::MyWidget(QMainWindow *w)
*/
int main(void)
{
+ QApplication::setStyle(QStyleFactory::create("Wind ows"));
+
char *argv[] = {"but.qt4", "-qws"};
int argc = sizeof(argv)/sizeof(argv[0]);
QApplication app(argc, argv);

Now the QT-4-based application works as quickly as the QT-2-based one: the text color of the buttons pressed are changed without any delays, and there are no delays when I draw my full-screen picture, and redraw the main screen with buttons when the picture is pressed. I guess that the origin of the delays observed with the default Plastique style - is the gradient color of button backgrounds.

[alexpaul]

You use has the following features:

- EP9315 CPU (ARM920T SOM Linux), 200MHz, 16KB caches;
- SDRAM 64MB, 100MHz;
- LCD 800x600, 16bpp;
- touch-screen (tslib-1.0);
- running with Linux kernel 2.6.20.21.

Qt4 is of course much more complex than Qt2 but simply measuring the delay between pushing the button and seeing the result doesn't say anything about what is causing the delay. It might be either modifying the palette and all things that happen around it or the process of displaying the changes

[d_stranz]

@alexpaul: Please don't go around digging up long-dead posts and replying to them, especially if you aren't really adding anything new.

[anda_skoa]

@alexpaul: Please don't go around digging up long-dead posts and replying to them, especially if you aren't really adding anything new.

In this case clearly spam, the link is not at all to the module the text claims to be.
I moderated the post.

Cheers,
_