[Qgis-developer] keeping layer settings tab between layers and qgis sessions can cause problems when histogram tab is the last viewed

[Etienne Tourigny]

On Thu, May 10, 2012 at 10:03 AM, Etienne Tourigny
<etourigny.dev at gmail.com> wrote:
> You are right, that is the best approach.  However, it might be best
> to auto-load when the user actually switches to the tab.
>
> A pain gdal does not have an API to query if the histogram is already
> computed - this would require adding PAM-aware code to the gdal
> provider.
>

I need to correct myself - PamFindMatchingHistogram() is available in
gdal_pam.h and could be used to test if a cached histogram exists -
provided the raster is a pam raster.

However, it seems the raster provider uses the C GDAL API - rather
than the C++ API , could this be changed easily?

Etienne

> Etienne
>
> On Wed, May 9, 2012 at 9:53 PM, Nathan Woodrow <madmanwoo at gmail.com> wrote:
>> Generally it is good practice that the UI remembers where the user left it
>> last time.  In this case this has a bad user experience because of the slow
>> loading.  My suggestion would be to just add a "Load histogram" button in
>> the histogram tab that loads the histogram rather then when the tab is
>> switched to.  This way even if the histogram tab is remembered as the
>> current tab it will load like normal and user has to click "Load histogram"
>> to show it.
>>
>> - Nathan
>>
>>
>> On Thu, May 10, 2012 at 10:49 AM, Etienne Tourigny <etourigny.dev at gmail.com>
>> wrote:
>>>
>>> I agree that this should not happen, should the default be always open
>>> the first tab, or only when the histogram tab was previously selected?
>>>
>>> Unfortunately there is no function in the provider API to know if
>>> there is a cached histogram, so it would be better to never allow the
>>> properties window to start on the histogram tab.
>>>
>>> I have implemented this in a branch of mine to improve the histogram
>>> tab, here is a snippet:
>>>
>>> -  tabBar->setCurrentIndex( settings.value(
>>> "/Windows/RasterLayerProperties/row" ).toInt() );
>>> +  int currentTabIndex = settings.value(
>>> "/Windows/RasterLayerProperties/row" ).toInt();
>>> +  // if current tab is disabled, use first tab
>>> +  if ( ! tabBar->widget( currentTabIndex )->isEnabled() )
>>> +    currentTabIndex = 0;
>>> +  // if current tab is histogram, use first tab (to avoid long
>>> histogram queries)
>>> +  // there is currently no way to know if there ia a cached histogram
>>>   int myHistogramTab = 6;
>>> -  if ( tabBar->currentIndex() == myHistogramTab )
>>> -  {
>>> -    refreshHistogram();
>>> -  }
>>> +  if ( currentTabIndex == myHistogramTab )
>>> +    currentTabIndex = 0;
>>> +  tabBar->setCurrentIndex( currentTabIndex );
>>>
>>>
>>> Etienne
>>>
>>> On Mon, May 7, 2012 at 10:15 AM, G. Allegri <giohappy at gmail.com> wrote:
>>> > A complex object to say something simple :(
>>> > When a user opens a layer settings window and hits a tab, the same tab
>>> > index
>>> > is kept when opening another layer settings, or in a new qgis sessions.
>>> > I had a small raster layer, and I opened the histogram tab.
>>> > The today I've opened a big raster layer, and opening the layer settings
>>> > caused my pc running and running, till a complete qgis crash.
>>> > I supposed it was something with the settings, so I opened the smalle
>>> > raster, changed the tab to Style, then I was able to open the large
>>> > raster
>>> > settings
>>> > It's corner case probably, and qgis shouldn't crash with huge raster
>>> > histograms. Anyway, opening the layer settings to the frist tab would
>>> > avoid
>>> > heartbreaks :)
>>> >
>>> > giovanni
>>> >
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>>
>>