QGIS » QGIS Application

if this didn't happened in previous qgis releases then the ticket should be tagged as blocker.

This behaviour started after version 2.2. Many options were added under "rendering" and that broke the basic redrawing of rasters.

Well I conducted a training for close to 60 people last week. In that group about 20 people had this problem. I have started providing 2.2 with the latest QGIS to ensure the participants can continue working with raster images.

A sample image which caused the problem:
https://drive.google.com/file/d/0B_ZSxE5g2YppVV9DcTRnM2VCeVk/view?usp=sharing

I had created pyramids for some and then deleted them. That did not seem to change anything

Sitansu Pattnaik wrote:

Well I conducted a training for close to 60 people last week. In that group about 20 people had this problem. I have started providing 2.2 with the latest QGIS to ensure the participants can continue working with raster images.

what could have had in common that 20 computers/installations?

Another update with some more observations:
I completely uninstalled the Nvidia graphics drivers and the problem still occurred, so it does not seem to be related to a particular graphics driver.
Resizing the overview window will also make the raster in the overview disappear and reappear frequently.
I have tested both with and without pyramid layers, with / without render caching enabled, and with / without parallel rendering with no apparent change in behaviour.
The raster drawing seems to draw the rescaled original view (i.e. when zooming out, the scaled-down version of the original view is shown in the middle of the window) and then it disappears.
Is there any additional testing that I could do to help narrow down this issue?

Giovanni Manghi wrote:

Sitansu Pattnaik wrote:

Well I conducted a training for close to 60 people last week. In that group about 20 people had this problem. I have started providing 2.2 with the latest QGIS to ensure the participants can continue working with raster images.

what could have had in common that 20 computers/installations?

I tried to find out. The only common factor was that they had RAM of 3 or 4 GB and not more. But this is the common configuration Laptops which are purchased by students in India.Most had Windows 7 but a few had XP and 8.1.

Sorry but I could not find anything definitive.

I think I've found something that might help in narrowing down the issue. Based on some googling on the QT graphics system, I set the environment variable QT_GRAPHICSSYSTEM=raster and it seems to have fixed the problem. Could it be possible that there is an issue with the QT native painter and some graphics cards / drivers? In the meantime, setting this variable in the batch script that starts QGIS might be a workaround.

I'm having the same issue with my laptop, in W7 and W10 64 bits, with an ATI graphics card. This issue doesn't affect 4 bands images it only seems to happen with 7-8 bands images (landsat 8, WV2 8 bands). The QT_GRAPHICSSYSTEM variable doesn't fix anything in my case. I've seen people with different OS (including MAC) with the same issue, all laptops. RAM in my case is 8 GB so i would discard something related with RAM. This doesn't happen in my desktop PC so i would think it's something related with laptops. What do all these laptops have in common? Maybe the Intel graphics card (4000 or higher) included in i7 and i5 processors.

Please test with tomorrow's nightly builds and confirm whether the possible fix has worked