OpenGL Canvas or Not

David Revoy davidrevoy at
Fri Oct 18 09:16:34 UTC 2013

Hey Enrico ! here are my additional thought on your questions :

On Fri, Oct 18, 2013 at 9:38 AM, Enrico Guarnieri <ico.dy.ta at>wrote:

> 1st problem
> Processor    4x Intel(R) Core(TM) i5 CPU 650 @ 3.20GHz
> Memory    8GB
> Operating System    Ubuntu 12.04.3 LTS
Ubuntu 12.04 doesn't provide VC librairies afaik  ( and also got a lot of
librairies outdated, might also be a problem to follow Git master. )  ; you
probably already built VC yourself ; but if not your CPU ( a strong one )
might gain a big improvement of performances. For the 'buntus , I made this
script by the past to auto build VC 7.0 Git master :

2nd problem:
> Why the software mode is so slow in rotating and zooming the viewport? In
> other painting programs is very fast without gpu acceleration using a
> single core too!
I always experienced Qpainter (CPU canvas) to get more slower for
continuous zoom or continuous rotation ; it's true it's really smooth with
GPU ; and smoother with an Intel GPU and libre driver. ( I discovered it in
our London trip on Boud's computer ; then I bought the week after the same
hardware :D )

> 3rd Problem:
> Why the painting in the viewport is "blurry" in opengl canvas and in
> software mode as well? For example Gimp have a very sharp and precise
> rendering...
As Boudewijn linked ; a bug report is open about it :
Trilinear is always blury ; at any zoom level. Qpainter(CPU) is a bit less
Choosing "Bilinear" is actually the best option ; from 100% to 50% you'll
match the Gimp/Mypaint/Azdrawing quality.
Above 50% ( 33% , 25%, 17%, 12% ) ; the Bilinear filter will bug ; and the
rendering will be bad ( total aliasing ). Equal to 'Nearest'.
I adapted my workflow to paint using mostly 50% as a workaround. And when I
do sketch/line art at 25% , I have a workaround changing the code , as I
explain on the bug report.
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