Damn! This used to be really good -- http://www.valdyas.org/fading/index.cgi/hacking/krita/progress_2007_2.html. Dmitry, do you have any idea what happened here? It doesn't seem to matter whether I use opengl or qpainter canvas.

Created attachment 61243 [details]
same image on my laptop, qpainter canvas

Created attachment 61244 [details]
same image 25%, opengl canvas

Created attachment 61254 [details]
with an old version

Around version 2.2 alpha 1 (commit 376aaf72acf2dae518d279aba4cca7ea00a54cce) it was much better, see attachment.

Thanks boud for the confirmation and also for the documentation. 
Good job done in 2007. 

Good to see this bug was already solved and in a very good way at this moment. The anti-aliasing looks very good :D This is surely very pleasant to ink comics or practising thin line-art with a display like this on screen. 
I hope it will not be a huge developpement work to move back to 2.2a1 way to display zoom out.

Direct comparison... http://www.valdyas.org/~boud/comparison_old_new.png

I'm not sure how hard it is to fix the display, unfortunately :-(.

Created attachment 61255 [details]
the comparison of old, new-qpainter, new-opengl

Just a summary:

version that used to work:
376aaf72acf2dae518d279aba4cca7ea00a54cce -- March 5. 2010

the comparison of old, new-qpainter, new-opengl is in attachement

Created attachment 61256 [details]
the comparison of old, new-qpainter, new-opengl

Just a summary:

version that used to work:
376aaf72acf2dae518d279aba4cca7ea00a54cce -- March 5. 2010

the comparison of old, new-qpainter, new-opengl is in attachement

More comparison images at http://www.valdyas.org/~boud/old_canvas_comparison_2.png

Cool, thanks to your picture,  I can see Qpainter_mip_map-true does the same job as Photoshop CS2 ( zoom at 400% the PsCs2 picture and compare, same pixels greyed and way to AA  ; http://david.revoy.free.fr/forums/krita/anti-aa-test/anti-aliasing_compare_deevad.png )witch is not optimum compare to what Mypaint and Gimp have . But, it can look good and suffisant ( no PS user complain about it ? they should :D ) . I think Gimp team did a very good job for their AA of viewport, they may be have the best 2D rendering on screen at any zooming. I wonder what is the cost in performance/resources of a rendering like this. May be it has a huge impact on drawing ?

 From the 2007 Krita article about AA Boud linked in this thread ; Krita looked to have even better AA rendering than this. 

For the 3 others, they look to do something a bit better than my actual test with Krita, but still too much crispy.

Git commit c0282232bc535b3aabffe4bfda6cefdc1db7c256 by Boudewijn Rempt.
Committed on 23/06/2011 at 15:38.
Pushed by rempt into branch 'master'.

KisCanvas: use QImage to scale the patches, not QPainter

QPainter's smooth scaling is much, much worse than QImage's smooth
scaling, so prescale the patch before painting.

The OpenGL canvas is unaffected and still has crap anti-aliasing, but
that's the price of OpenGL.
CCBUG:276278

M  +34   -2    krita/ui/canvas/kis_image_patch.cpp     
M  +8    -0    krita/ui/canvas/kis_image_patch.h     
M  +5    -1    krita/ui/canvas/kis_prescaled_projection.cpp     

http://commits.kde.org/calligra/c0282232bc535b3aabffe4bfda6cefdc1db7c256

This is as good as it gets -- maybe for 2.5 or so we'll invent a new way of scaling.

Created attachment 77125 [details]
rendering comparison : Qpainter is blury for line art

I just reopen this one ( check the previous attachment ).
Qpainter is blury for line art, and also the only alternative for Windows users.

I also have some comparison to Krita's scale of viewport:
Original image: https://dl.dropboxusercontent.com/u/26887202/blender/kc_buildings_001_castle3_lev122.png

Scale of 66,7%(left is Krita, right is Gimp): https://dl.dropboxusercontent.com/u/26887202/blender/ee1.png

The same is with OpenGL and without.

I noticed a negative change lastly ( compiled Git source, nvidia-current on 12.10 'buntu system. Mint KDE 14 )
OpenGL viewport tend to have a very noisy AntiAliasing when 33% zoomed out and lower zoom ( ex : http://i.imgur.com/MovJUDJ.jpg ).
It was quite annoying, as it made me smooth/blur all textures of an artwork on finalising step for nothing ; because I thought they where too noisy or crispy.

Hi David, did you try to switch Trilinear filtering on? 
Screeen http://i.imgur.com/I4CGnDC.png

Boud works on different filter types(more sharpen than trilinear). But his new Opengl brunch is still in development and it has some issues with zooming yet.

Hi Paul, thanks for the tip ! I never thought to activating 'Trilinear' ; and I have indeed a very good rendering now with it. 
By the past, 'Trilinear' was bugged with my Nvidia driver, and resulted to a lot of slow-down and crunched some wacom input and bring random noise to the line smoothing. I'm happy to see it's not the case anymore.

Cool that it helps you!
The problem with Trilinear is that it makes very blurry with zoom less than 70%.  But Boud works on other antializing filters like Nearest-Mipmap. I hope he will commit them too.

Update info : I was annoyed back since around 10 days that the canvas get blury again. To get the more sharp rendering back, desactivating 'Trilinear' works. ( tested on Linux ; 2 computers Intel HD2400 and Nvidia GT220 , 3.10 driver ).

The qpainter canvas rendering hasn't changed at all (unless a Qt upgrade changed some algorithm in there), the opengl canvas rendering changed Sunday evening.

Thanks Boud for the infos. I just saw on 'git log' the new work done on OpenGL. I'll update later this week after finishing my production deadlines. ( in comment 21 ; both my computers tested had a Git version from middle of last week , before the update, so my feedback is not related to new OpenGL ).

*** This bug has been marked as a duplicate of bug 313502 ***