FW: broken PNG files with GD backend

Some notes on compiling GD backend for windows.

1) _gdmodule.c needs to be modified in 2 places to compile on windows

  a) line 1888 PyObject_HEAD_INIT() needs to passed a NULL. This
is in the Python docs.
  static PyTypeObject Imagetype = {
        0, /*ob_size*/

  b) the init_gd function ( line 1957 ) needs to have
'_declspec(dllexport)' added to the declaration.

/* Initialization function for the module (*must* be called init_gd) */
void _declspec(dllexport) init_gd(void)

2) This one took me a long time to figure out. For some reason opening
a windows file in Python with 'wb' permission will cause the png files
to be corrupted above a certain image size. If you pass the filename to
gdmodule, then the gdmodule opens the file and it works. I imagine that
the python call "open( 'filename', 'wb' )" just calls fopen, furthermore
I thought that binary mode only applied to reading files. At any rate,
I have no idea why this doesn't work in this case but it doesn't. To
get it to work, I had to change line 261 in backends_gd.py to pass the
filename rather than a file object, this is the only modification to
Matplotlib I had to make.

        im.writePng( filename )

#2 above is the answer to the problem in my original post. However I
have another question. When I set the ylabel rotation to be horizontal,
the beginning of the text is truncated ( the width of the border does
not compensate ). I'm happy to set it wider but am wondering how ( what
controls the width of the area where the labels gets written ). I also
noticed that title of the graph ( with the horizontal alignment set to
bottom ) is too close to the top of the graph itself, is there a way to
pad that?



-----Original Message-----
From: John Hunter [mailto:jdhunter@…8…]
Sent: Friday, January 23, 2004 6:58 AM
To: Kuzminski, Stefan R
Cc: matplotlib-users@lists.sourceforge.net
Subject: Re: [Matplotlib-users] broken PNG files with GD backend

"Kuzminski," == Kuzminski, Stefan R <SKuzminski@...79...>


    > Now on to my specific problem. I'm using the GD
    > backend on Windows with Matplotlib 0.41.

First things first -- I haven't succeeded in getting the gd backend
compiled on windows. If you have some expertise here and are willing
to share, or better yet build a gdmodule and gd installer that I can
put on the website, I would be very much obliged! I contacted the
gdmodule maintainer some time ago over this issue and he had never
built it on windows either. In my googling, I discovered the perl gd
module for windows and following their lead, succeeded in building gd
lib, but ran into some troubles (can't remember what) building

    > If I set the dpi to over 60 the png file that gets
    > generated is 'empty', it's only 17 bytes long. As soon
    > as I drop he DPI to below 65 or so, I get the image
    > file correctly. This is with the simple_plot.py
    > example.

Now on to your problem. Is there a typo here? You say over 60 is
empty and under 65 is ok ?? Can you send me a script which replicates
the problem, with the two calls to savefig, one which has the problem
and which does not. Then I can begin to diagnose the problem; see if
it occurs under linux, see if it's a gd problem, see if it's a problem
on my end, etc....

Are you using matplotlib + GD for a web app server?

John Hunter