After a bit of playing around it seems that wxGCDC uses a similar trick to some
Plplot drivers in that it pretends to have a bigger size than the bitmap it is
drawing on (10000x10000 units). This means we do get subpixel accuracy and
better than 1 pixel accuracy line widths. However it is up to the user to
define the scale factor to convert to bitmap pixels which is why I was getting
a blank canvas - my drawing was based on the "fake" size so missed the bitmap.
Now I have this worked out I can now send a wxGCDC to plplot using backend=0
and get sensible output. There may be some tweeks needed to ensure the line
width is correct. But providing things work on Linux I think the
wxGraphicsContext backend can be made essentially redundant.
The only issue is implementation. Looking at some wxWidgets 2.9 code it seems
wxGCDC is able to wrap other wxDCs such as wxPrintDC as well as wxMemoryDC, and
the list is likely to expand I imagine. I think the user might want three
options:
1) Pass an ordinary wxDC to Plplot
2) Pass a wxMemoryDC to Plplot but get wxGCDC rendering - i.e. identical
functionality to current backend=2 functionality.
3a) Pass another wxDC in and have it wrapped by wxGCDC or 3b) have users wrap a
wxDC in a wxGCDC themselves and pass this to Plplot.
1) and 2) can be acheived by keeping the backend flag and replacing private
Plplot code. This would maintain backwards compatibility for users of the
current system.
We probably should support 3b) better than we currently do as currently the
user has to set the scaling before passing the wxGCDC to Plplot. It would be
better if Plplot did this and it would be easy to do I think. 3a) could be
done, but we'd need the user to pass another flag indicating what type of wxDC
they have passed so that it can be cast as the correct pointer. If the number
of wxDCs which can be wrapped by wxGCDC increases then we'd need to add extra
options. This doesn't sound like a good plan to me.
All these options could be implemented with one set of rendering code and an if
statement at initialisation. So much cleaner in terms of maintenance.
Phil
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