Hi all, thanks for the efforts put in this topic. A few hours after my initial post, I had a working quick&dirty cut&paste solution with minor source code changes without really knowing what I'm doing...
I'm glad that someone with a deeper understanding of the mpl internals is working on a mpl conform solution. I will subscribe to matplotlib-devel to keep track of the changes and help to test patches. Regards Simon Paul Ivanov wrote: > Hey John and the rest of the MPL gang: > > I've made the changes you suggested, but the problem is looking to be > deeper than it seemed. I'm also moving this conversation to > matplotlib-devel, since that's probably the more appropriate place for > it. > > This updated patch allows for the creation of colormaps with various > alphas, but there is likely more work to be done so that mpl can > consistently make use of it (because it seems like all built-in cmaps > are RGB, not RGBA). > > In trying to come up with an example that exercises the new > capabilities, I found out that methods like scatter and countourf modify > the colormap you give them and reset all of the alpha values to 1. > > I think this is because inside collections, we pass self._alpha, which > is the Artist._alpha, and 1.0 by default, when making calls such > as: > _colors.colorConverter.to_rgba_array(c, self._alpha) > > ...Thus resetting all of alpha values. > > I was able to get around this by allowing collections to take on an > alpha value of None, and then passing alpha=None to scatter and > countourf, for example. There are probably other places where such a > change should be done, unless someone has a better idea for how do do > this. I updated examples/pylab/plot_scatter.py to show off the new > capability. > > Another thing that I was unable to get around is that if you now make a > plot using the same colormap but omit the alpha=None parameter, or set > it to something other than None, it will reset the alpha values on the > previous plot: > > figure(2) > c = scatter(theta, r, c=colors, s=area,cmap=myColormap,alpha=None) > > will do the right thing, but calling scatter without alpha=None > > figure(3) > d = scatter(theta, r, c=colors, s=area,cmap=myColormap) > or > d = scatter(theta, r, c=colors, s=area,cmap=myColormap, alpha=.5) > > will reset all of the alpha values in myColormap to 1 or .5. > You can do c.cmap._init() to reset its original alpha values, and if you > force a redraw on figure(2) (by panning or zooming on it, for example), > it will look right again. However, if you go and fiddle with figure(3) > (pan/zoom), and come back to figure(2), panning or zooming will > cause all of the alpha values will be reset again. > > I'm not sure if it would be worth it to make a copy of the colormap to > prevent this from happening. Anyone have thoughts on this? > > (the full example of this is commented with FIXME: in polar_scatter.py) > > best, > Paul Ivanov > > > John Hunter, on 2008-11-23 07:36, wrote: >> On Sun, Nov 23, 2008 at 2:01 AM, Paul Ivanov <[EMAIL PROTECTED]> wrote: >>> I took a stab at it, how does this look? >>> >>> I also took the liberty of adding alpha to LinearSegmentedColormap and >>> updated its docstring changing two somewhat ambiguous uses of the word >>> 'entry' with 'key' and 'value'. >> Hey Paul, >> >> Thanks for taking this on. I haven't tested this but I read the patch >> and have some inline comments below. Some additional comments: >> >> * the patch should include a section in the CHANGELOG and >> API_CHANGES letting people know what is different. >> >> * you should run examples/tests/backend_driver.py and make sure all >> the examples still run, checking the output of some of the mappable >> types (images, scaltter, pcolor...) >> >> * it would be nice to have an example in the examples dir which >> exercises the new capabilities. >> >> See also, in case you haven't, >> http://matplotlib.sourceforge.net/devel/coding_guide.html, which >> covers some of this in more detail. >> >> Thanks again! Comments below: >> >> Index: lib/matplotlib/colors.py >> =================================================================== >> --- lib/matplotlib/colors.py (revision 6431) >> +++ lib/matplotlib/colors.py (working copy) >> @@ -452,7 +452,7 @@ >> self._isinit = False >> >> >> - def __call__(self, X, alpha=1.0, bytes=False): >> + def __call__(self, X, alpha=None, bytes=False): >> """ >> *X* is either a scalar or an array (of any dimension). >> If scalar, a tuple of rgba values is returned, otherwise >> @@ -466,9 +466,10 @@ >> """ >> You need to document what alpha can be here: what does None mean, can >> it be an array, scalar, etc... >> >> if not self._isinit: self._init() >> - alpha = min(alpha, 1.0) # alpha must be between 0 and 1 >> - alpha = max(alpha, 0.0) >> - self._lut[:-3, -1] = alpha >> + if alpha: >> >> I prefer to explicitly use "if alpha is None", since there are other >> things that would test False (0, [], '') that you probably don't mean. >> >> + alpha = min(alpha, 1.0) # alpha must be between 0 and 1 >> + alpha = max(alpha, 0.0) >> >> You should be able to use np.clip(alpha, 0, 1) here, but we should >> consider instead raising for illegal alpha values since this will be >> more helpful to the user. I realize some of this is inherited code >> from before your changes, but we can improve it while making this >> patch. >> >> + self._lut[:-3, -1] = alpha >> mask_bad = None >> if not cbook.iterable(X): >> vtype = 'scalar' >> @@ -558,9 +559,10 @@ >> def __init__(self, name, segmentdata, N=256): >> """Create color map from linear mapping segments >> >> - segmentdata argument is a dictionary with a red, green and blue >> - entries. Each entry should be a list of *x*, *y0*, *y1* tuples, >> - forming rows in a table. >> + segmentdata argument is a dictionary with red, green and blue >> + keys. An optional alpha key is also supported. Each value >> + should be a list of *x*, *y0*, *y1* tuples, forming rows in a >> + table. >> >> Example: suppose you want red to increase from 0 to 1 over >> the bottom half, green to do the same over the middle half, >> @@ -606,6 +608,8 @@ >> self._lut[:-3, 0] = makeMappingArray(self.N, >> self._segmentdata['red']) >> self._lut[:-3, 1] = makeMappingArray(self.N, >> self._segmentdata['green']) >> self._lut[:-3, 2] = makeMappingArray(self.N, >> self._segmentdata['blue']) >> + if self._segmentdata.has_key('alpha'): >> + self._lut[:-3, 3] = makeMappingArray(self.N, >> self._segmentdata['blue']) >> >> Is this what you meant? I think you would use 'alpha' rather than >> 'blue' here, no? >> >> self._isinit = True >> self._set_extremes() >> >> @@ -664,11 +668,10 @@ >> >> >> def _init(self): >> - rgb = np.array([colorConverter.to_rgb(c) >> + rgba = np.array([colorConverter.to_rgba(c) >> for c in self.colors], np.float) >> self._lut = np.zeros((self.N + 3, 4), np.float) >> - self._lut[:-3, :-1] = rgb >> - self._lut[:-3, -1] = 1 >> + self._lut[:-3] = rgba >> self._isinit = True >> self._set_extremes() > ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Matplotlib-devel mailing list Matplotlib-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-devel
