Dane Springmeyer wrote:
On Jul 17, 2010, at 12:22 PM, Jon Burgess wrote:
On Sat, 2010-07-17 at 12:35 +0800, feverzsj wrote:
hi, list:
some python code:
im = mapnik.Image(self.map.width, self.map.height)
mapnik.render(self.map, im)
qim = QImage()
qim.loadFromData(QByteArray(im.tostring('png')))
The questions are: why we should pass a string 'png'? What is stored
in mapnik.Image? What is done in the tostring()?
The mapnik.Image is a wrapper around the raw bitmap data of the rendered
image. The tosting('png') asks mapnik to convert this into a PNG image
and return it as a python string. This is then converted into a QT byte
array and then finally converted into a QImage.
A PNG image was probably chosen as a simple standard format which Mapnik
can create and QT can read. This method is fairly simple and reliable
but not the most efficient.
It may be possible to directly convert the raw bitmap data from Mapnik
into a QImage but it would need some careful reading of the docs to
figure out if they are compatible. This approach is taken by the C++
Mapnik viewer application:
http://trac.mapnik.org/browser/trunk/demo/viewer/mapwidget.cpp#L460
Nice spot Jon!
This seems to work:
instead of:
self.qim.loadFromData(QByteArray(im.tostring('png')))
do:
self.qim = QImage(im.tostring(),self.map.width,
self.map.height,QImage.Format_ARGB32).rgbSwapped()
I've tired this, but seems not working. QPixmap also failed.
-- Regards, zsj
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