How to get qtdemo with reasonable speed?

**ponto** · 18th February 2006, 11:13

I've compiled Qt 4.1 on several Linux machines and tried the demos with qtdemo. On each machine the demos were slow as hell, with about a framerate of 4 fps.

Does anyone know what the prerequisites are to get the demos at a reasonable speed?

**yop** · 18th February 2006, 12:47

Are we talking about openGL? What's the output of:
glxinfo | grep direct

**ponto** · 18th February 2006, 13:32

Originally Posted by yop

Are we talking about openGL? What's the output of:
glxinfo | grep direct

Here is the output

Qt Code:

Switch view

ponto@burns:~> glxinfo | grep direct
direct rendering: Yes

ponto@burns:~> glxinfo | grep direct
direct rendering: Yes

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I do not think that opengl is a problem here, because games like Unreal Tournament 2003 are quite fast here. I also do not know whether the qtdemo app uses opengl.

**wysota** · 20th February 2006, 19:41

Did you compile the demo in debug or release mode? (Simply speaking, is the binary of it "huge" (2MB) or "small" (200kB)?) It might be compiled in debug mode, which causes a major slowdown.

**ponto** · 20th February 2006, 20:28

Originally Posted by wysota

Did you compile the demo in debug or release mode? (Simply speaking, is the binary of it "huge" (2MB) or "small" (200kB)?) It might be compiled in debug mode, which causes a major slowdown.

I see that the qtdemo executable itself is linked against debug versions of the Qt libraries. Howver the demos themselves are linked against the release libraries. I also checked the compilation process and see that optimized binaries are build.

**wysota** · 20th February 2006, 20:54

But is it just the qtdemo that is slow or all examples are slow?

**ponto** · 20th February 2006, 21:50

Originally Posted by wysota

But is it just the qtdemo that is slow or all examples are slow?

Most examples are as slow as qtdemo. For example the composite demo is really slow. Also slow are deform and pathstroke.
Mainwindow is not really slow but too slow for the shown effect.

**wysota** · 20th February 2006, 23:28

Composite can be a bit slow, although I don't have direct rendering working, so that may be because of the driver.

**nuntius** · 31st May 2006, 10:25

Disclaimer: X11 only

The source for qtdemo is in QTDIR/examples/tools/qtdemo.
Search for "slow" in displaywidget.cpp.
This message popped up *once* for me, I responded properly, and qtdemo ran fast. Every other time, its been slow as molasses.