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Old 07-19-10, 07:36 PM   #1
cyrion
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Unhappy Qt apps still slow with non-antialiased fonts (256.35)

Everything is in the title

Will this bug be fixed one day?
Gnome apps don't have this problem so I wonder whether this problem really comes from nvidia..

D.
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Old 07-20-10, 04:52 AM   #2
hl_
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Default Re: Qt apps still slow with non-antialiased fonts (256.35)

Qt is using Xrender w/ A1 pictures for non-antialiased fonts. It shouldn't do that, as modern hardware is incapable of accelerating operations that involve such formats, triggering software fallbacks in one way or another. I'd say it's a Qt problem.
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Old 07-20-10, 08:43 AM   #3
cyrion
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Default Re: Qt apps still slow with non-antialiased fonts (256.35)

This explains why using "-graphicssystem raster" on a qt app make it render a lot faster.

So the problem comes from both Qt and NVidia:
- qt should use another format for nvidia cards
- and/or nvidia should support A1 images

Thank for the explanation, I'm moving to Qt forums.
D.
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Old 07-28-10, 05:55 PM   #4
Linuxhippy
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Default Re: Qt apps still slow with non-antialiased fonts (256.35)

Quote:
Originally Posted by cyrion View Post
Thank for the explanation, I'm moving to Qt forums.
The usual answer (official?) is, that you should use the RASTER engine,
and Nokia won't enhance the XRENDER engine, because XRender is slow anyway.

Truth is, XRender was horrible slow in the past when QT's XRender engine was written before hardware acceleraration was supported through EXA/UXA and/or NVidia's binary driver.
However, QT uses Xrender in some quite stupid ways - sometimes (like your A1 ussue) effectivly preventing proper hw accaleration.

- Clemens
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Old 07-28-10, 08:08 PM   #5
Sean_W
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Default Re: Qt apps still slow with non-antialiased fonts (256.35)

XRender isn't slow if you have a good CPU and on Intel onboard cards is actually fast. Might you, XFCE's compositor is smooth using an old computer and that uses XRender.

The Nouveau driver is fast with XRender as well. Kwin's compositing using XRender is pretty good, last time I tried it in KDE 4.4.
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Old 07-28-10, 10:36 PM   #6
hl_
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Default Re: Qt apps still slow with non-antialiased fonts (256.35)

Uhm, the point of XRender is to offload rendering tasks to the GPU. Of course software fallbacks get faster if you have a fast CPU, but that's not the idea.

Many drivers only seem "fast" at XRender because they don't accelerate much and software fallbacks are used all the time.

NVidia's drivers and (starting with ~2.11) Intel's drivers accelerate most operations that are feasible, given the hardware. The downside is that operations in the XRender pipe that cannot be accelerated and cause software fallbacks can be really slow, as pixmaps need to be transferred from gpu to host and back again. Sometimes even multiple times; this is referred to as migration ping-pong. Drivers try to detect and workaround such situations, but that's not always possible.

TL;DR if XRender hardware acceleration is supported, works and used correctly, it is ****ing fast. If not, it can cause pathologically slow software fallbacks.
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Old 07-29-10, 09:14 AM   #7
wantilles
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Default Re: Qt apps still slow with non-antialiased fonts (256.35)

After almost 15 years with unicode and truetype fonts, who is so stupid, to use non-antialised fonts?

Get out of the cave and the ice age.
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Old 07-29-10, 03:29 PM   #8
Linuxhippy
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Default Re: Qt apps still slow with non-antialiased fonts (256.35)

Quote:
Originally Posted by wantilles View Post
After almost 15 years with unicode and truetype fonts, who is so stupid, to use non-antialised fonts?
What has unicode and truetype to do with wether someone prefers antialiased or non-antialiased glyphs? I would say its simply a personal preference. (and I have to admin some fonts look really pretty even non-antialiased)


- Clemens
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Old 07-29-10, 03:55 PM   #9
hl_
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Default Re: Qt apps still slow with non-antialiased fonts (256.35)

Especially in terminals and for programming, non-antialiased bitmap fonts can be very nice. Take a look at the great "Terminus" font, for example.
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