Re: [matplotlib-devel] First cut on a QtAgg backend

[John H. <jdh...@ac...>]

>>>>> "John" == John Hunter <jdh...@ac...> writes:

    John>   * The only explanation I can think of for why the colors
    John> are wrong is that qt has a different byte order for images
    John> than you are getting from agg (is could it be bgra instead
    John> of rgba, or that something is wrong with the endianess...)
    John> If you need a different byte ordering /pixel format, I can
    John> provide the required method in the agg backend.  I note that
    John> the saved figures *do* have the right color scheme, which
    John> supports this idea.

Another clue that endianess is playing a role here is that the colors
are dramatically different on OSX (which I tested yesterday) ans linux
which I tested today.  But I think it's more than an endian problem,
because the colors are wrong on both platforms.  On linux, it looks
like the endianess is right, but it's an rgb versus bgr thing, since
the colors are backwards on

    from pylab import *
    subplot(211)
    plot([1,2,3], color='red')

    subplot(212)
    plot([1,2,3], color='blue')

    show()

On OSX, it looks like the endianess is wrong because the colors are
really off...

Also, I took a quick at the qimage class docs at
http://doc.trolltech.com/3.3/qimage.html and saw

 It is one of the two classes Qt provides for dealing with images, the
 other being QPixmap. QImage is designed and optimized for I/O and for
 direct pixel access/manipulation. QPixmap is designed and optimized
 for drawing. There are (slow) functions to convert between QImage and
 QPixmap: QPixmap::convertToImage() and QPixmap::convertFromImage().

Does this suggest that QPixmap might be more appropriate / faster
since you don't need to do the individual pixel manipulation provided
by QImage (spoken as a total qt newbie, so please forgive any
stupidities on my part...)


An unrelated observation regarding event handling: the qt backend is
not connecting to mouse motion unless a pan/zoom button is pressed and
released, eg coords_demo.py does not work properly.

Cheers!
JDH