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[Tim Sutton]

Hi

On Wed, Mar 2, 2011 at 11:19 PM, Alister Hood
<alister.hood at synergine.com> wrote:

8<-------------snip---------------

>>Hi Tim
>>
>>yes, it's more costly also for symbols with just one symbol layer. The
>>idea is that the features in current view are loaded into memory first
>>(with a reference to symbol that will be used) and then rendered. So
>>there is some memory overhead and some cpu overhead (unsure about the
>>total amount). The case with just one symbol layer could be probably
>>optimized to some degree.
>
> Are you sure it needs to be optimised?  When there is only one symbol
> layer the final appearance always seems to be the same, whether symbol
> layers are turned on or not.  If this is the case, couldn't symbol
> layering just be ignored when there is only one?
> Am I missing something?
>
> Alister
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>

Alister from my understanding of it, even if there is a single layer,
with layer levels turned on, QGIS tries to load all the features into
memory first resulting in some overhead. I suspect in some situations
this may actually render *quicker* (untested) but for large datasets
where a lot of swapping out of ram to disk needs to happen, it could
kill performance somewhat. The optimisation in this case may simply be
'if there is one layer level. render as if layer levels are disabled'.
Martin may have further comments.

Regards

Tim
-- 
Tim Sutton - QGIS Project Steering Committee Member (Release  Manager)
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