Hi Jörg,
On 22/04/16 18:24, Jörg Habenicht wrote:
Hi Matthias,
Am 22.04.2016 um 17:20 schrieb Matthias Kuhn:
Hi,
I don't know the server code very well, so I may be wrong, but I think
that making the server multithreaded rendering (MTR) capable should be
possible. And while it is certainly often possible to increase the
performance with filtering, rules and caching there are certainly also
situations where MTR can help a server to generate quick responses (many
layers, few requests).
As far as I can see, the main task would be porting the code from
QgsMapRenderer to QgsMapRendererJob and QgsMapSettings. A first step
into this direction can be found in a recently closed pull request [1],
in particular this commit [2].
I'll have a look.
It seems to me I have to extract the code inside the loop (in
QgsMapRenderer::render(), "while ( li.hasPrevious() )") into a separate
method and call QtConcurrent on that.
You shouldn't have to deal directly with QtConcurrent, this code is
alredy present.
https://qgis.org/api/classQgsMapRendererJob.html#details
Have a look at QgsMapCanvas::refreshMap() which sets up a job and
connects the signal finished() to a local slot and continues execution.
On the server instead you probably want to use a QFutureWatcher with
waitForFinished() to wait for the painting job (with its threads) finish
before responding with the freshly painted image.
Matthias
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