Bug 333165

Summary:	Image artifacts while scrolling while zoomed out
Product:	[Applications] gwenview	Reporter:	Michael Reilly <OmnipotentEntity>
Component:	general	Assignee:	Gwenview Bugs <gwenview-bugs-null>
Status:	RESOLVED DUPLICATE
Severity:	normal	CC:	hein, lainlives, myriam
Priority:	NOR
Version:	4.11.5
Target Milestone:	---
Platform:	Kubuntu
OS:	Linux
URL:	https://dl.dropboxusercontent.com/u/6830171/canvas.png
Latest Commit:		Version Fixed In:

Description Michael Reilly 2014-04-07 16:38:22 UTC

When scrolling image with mouse at 50% zoom, image artifacts appear in newly uncovered areas.  Unsure if all images are affected or only pathological images such as the one linked.

Reproducible: Always

Steps to Reproduce:
1. Download the image (caution large image: 8127x8127)
2. Zoom to 50%
3. Click and drag image to the top left.
4. Drag image up and down and note the areas uncovered, they exhibit inconsistent striping with the rest of the image.
Actual Results:  
Gwenview shows artifacts while scrolling while zoomed to 50% using the click and drag technique.

Expected Results:  
I would expect no artifacts of this nature.

It's very difficult to see in normal usage of the program.  I've never noticed it for years until I ran across this, admittedly pathological image.

Unfortunately, I've been unable to build gwenview, so I cannot test against latest git or try to figure out what the issue is. I ran into some issues with cmake (KDE4_DATA_DIR-NOTFOUND) and could not find an authoratative source for the proper way to fix it.

Comment 1 Michael Reilly 2014-04-07 17:12:11 UTC

Because it's not easy to see, here's normal and bugged side by side:

http://imgur.com/a/pHfpj

Comment 2 Michael Reilly 2014-04-07 17:14:09 UTC

Able to reproduce on 4.13.0beta3 using the Trusty packages

Comment 3 Eike Hein 2014-04-07 17:21:48 UTC

I can reproduce that problem here with 4.12.2 - as the image is scrolled around and parts of it move outside the viewport bounds and back in, those areas are rasterized differently each time with artifacting parallel to the viewport edge. The artifacts are applied in intervals depending on the scroll speed, i.e. it probably happens at the frame rate of the canvas painting.

Comment 4 lainlives 2014-04-07 17:23:53 UTC

I reproduced it on gwenview 4.11.4

Seems to only work with the one linked PNG with zoom around 50%.

Comment 5 Eike Hein 2014-04-07 17:28:50 UTC

From a casual reading of the code it seems like Gwenview scales subrectangles of the image on demand as things scroll around, so the artifacting is probably a byproduct of the sampling not matching up as the rectangles get combined on the buffer.

Comment 6 Christoph Feck 2014-04-07 22:15:06 UTC


*** This bug has been marked as a duplicate of bug 271671 ***