Gerard Vermeulen wrote:

...

I just want to point out that PyQwt plots NumPy arrays. I have played a little bit with the Scipy-wxWindows interface, but it is no match for PyQwt (I display x-y data with 16000 points).

Thanks for the tip, I'll check it out. I think what you have there is that the plotting is all done at the C++ level, expecting some kind of sequence of data points. That's exactly what I want to adress with wxPython: being able to pass in a whole sequence and have the looping done at the C++ level.

Yes, I am using PyArray_ContiguousFromObject() to convert any sequence into a NumPy array before copying the data into Qwt's double arrays.

Have you ever tested whether it's fster or slower to plot data passed in as a list vs. a NumPy array?

I did not test it, but there is certainly more overhead if you pass a list or a tuple into PyArray_ContiguousFromObject() than a NumPy array

How do you access the data in the passed in sequence? Do you use: PySequence_GetItem ?

No, see above. The code looks like (in "sip" language, sip is a sort of swig, but more specialized to C++ and Qt): void setData(double *, double *, int); %MemberCode PyObject *xSeq, *ySeq; $C *ptr; if (sipParseArgs(&sipArgsParsed, sipArgs, "mOO", sipThisObj, sipClass_$C, &ptr, &xSeq, &ySeq)) { PyArrayObject *x = (PyArrayObject *) PyArray_ContiguousFromObject(xSeq, PyArray_DOUBLE, 1, 0); if (!(x)) return 0; PyArrayObject *y = (PyArrayObject *) PyArray_ContiguousFromObject(ySeq, PyArray_DOUBLE, 1, 0); if (!(y)) return 0; int size; Py_BEGIN_ALLOW_THREADS size = (x->dimensions[0] < y->dimensions[0]) ? x->dimensions[0] : y->dimensions[0]; ptr->setData((double*)(x->data), (double*)(y->data), size); Py_END_ALLOW_THREADS Py_DECREF(x); Py_DECREF(y); Py_INCREF(Py_None); return Py_None; } %End The setData calls copy the data.

thanks for the tip. Qwt (and PyQwt) look very nice, I may have to reconsider using PyQT!

Gerard

-Chris

...

Take a look at http://gerard.vermeulen.free.fr

PyQwt is an addon for PyQt (a Python wrapper for Qt) that knows nothing about NumPy

Maybe it is possible to make a NumPy plot add-on for wxWindows, too.

Gerard

On Wed, Jan 15, 2003 at 09:22:20AM -0800, Chris Barker wrote:

...

Hi folks,

I use Numeric an wxPython together a lot (of course I do, I use Numeric for everything!).

Unfortunately, since wxPython is not Numeric aware, you lose some real potential performance advantages. For example, I'm now working on expanding the extensions to graphics device contexts (DCs) so that you can draw a whole bunch of objects with a single Python call. The idea is that the looping can be done in C++, rather than Python, saving a lot of overhead of the loop itself, as well as the Python-wxWindows translation step.

For drawing thousands of points, the speed-up is substantial. It's less substantial on more complex objects (rectangles give a factor of two improvement for ~1000 objects), due to the longer time it takes to draw the object itself, rather than make the call.

Anyway, at the moment, Robin Dunn has the wrappers set up so that you can pass in a NumPy array (or, indeed, and sequence) rather than a list or tuple of coordinates, but it is faster to use a list than a NumPy array, because for arrays, it uses the generic PySequence_GetItem call. If we used the NumPy API directly, it should be faster than using a list, not slower! THis is how a representative section of the code looks now:

bool isFastSeq = PyList_Check(pyPoints) || PyTuple_Check(pyPoints); . . . // Get the point coordinants if (isFastSeq) { obj = PySequence_Fast_GET_ITEM(pyPoints, i); } else { obj = PySequence_GetItem(pyPoints, i); }

. . .

So you can see that if a NumPy array is passed in, PySequence_GetItem will be used.

What I would like to do is have an isNumPyArray check, and then access the NumPy array directly in that case.

The tricky part is that Robin does not want to have wxPython require Numeric. (Oh how I dream of the day that NumArray becomes part of the standard library!) How can I check if an Object is a NumPy array (and then use it as such), without including Numeric during compilation?

I know one option is to have condition compilation, with a NumPy and non-Numpy version, but Robin is managing a whole lot of different version as it is, and I don't think he wants to deal with twice as many!

Anyone have any ideas?

By the way, you can substitute NumArray for NumPy in this, as it is the wave of the future, and particularly if it would be easier.

-Chris

-- Christopher Barker, Ph.D. Oceanographer

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