Mailman 3 September 2019 - Matplotlib-devel

What is draw_path's transform's destination?
by Rob McDonald Sept. 24, 2019

Sept. 24, 2019

I'm implementing a custom path effect by inheriting from AbstractPathEffect and implementing draw_path as instructed here <https://matplotlib.org/api/patheffects_api.html#matplotlib.patheffects.Abst…>. That link references RenderBase.draw_path <https://matplotlib.org/api/backend_bases_api.html#matplotlib.backend_bases.…> to define the required interface. Unfortunately, I can't find anywhere in the associated documentation that tells me what the transform argument really entails. I've also read the transforms tutorial <https://matplotlib.org/tutorials/advanced/transforms_tutorial.html>, and while that explains the pipeline and all the intermediate transformations, it doesn't really settle what I have available to me in draw_path. It is clear that I can use it to transform coordinates from data to something -- but I don't know what to. For the big picture -- I am implementing a path effect to allow drawing hatched lines similar to this <https://www.mathworks.com/matlabcentral/fileexchange/29121-hatched-lines-an…>, which I did years ago in Matlab. Years before that, I've also done this in Java Graphics2D by implementing a custom stroke. (The Java approach is more applicable to the path effect approach, but I can't point to that code online anywhere.) Anyway, I have things mostly working -- and I am using the transform to go from data coordinates to something that looks orthogonal and reasonable on-screen. So, for minimum functionality, it works. However, I want to give the user the ability to control the length and spacing of the hatches -- which is in a coordinate system after the transformation is applied. So, in order to document this thing, I need to know what it is. Or, if there is a way to get intermediate stages of the transformation pipeline, that would work too. As for the user interface -- it seems to make the most sense to specify the hatch length and spacing in terms of something similar to a line width (typically points) or a marker size. I'm new to Python and matplotlib -- what is the Pythonic unit a user would expect to specify this in (and how do I achieve that with what is available in draw_path)? Thanks, Rob

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Masking in Matplotlib - Resetting the zorder of all pixels depending on their color value ?
by Carlos Baumann Sept. 23, 2019

Sept. 23, 2019

Hello Matplotlib Developers! 1) Matplotlib has a Clipping capability, but the "clipped" out areas use the same zorder, therefore rendering several overlapping polygonal shapes visible based on their zorder does not work in the areas where clipping was used to render one of them. 2) If it were possible to "reset" the zorder of a given pixel color (our background color) at any time while rendering, then we would have resolved the issue with clipping. We would not even need clipping as we could just use a given zorder value for the parts that define our desired mask areas, and a lower zorder for the part to be clipped, and after rendering the part in question, we change the zorder of all the "white" pixels to a low zorder value, and we have the masking capability working ! If this is not possible with the current version of Matplotlib, please can you help me giving me the code needed ? Example for illustration (see attached snapshot figure): '''Example of two overlapping squares having arbitrary openings in them. In this example the opening is just two smaller overlapping square, but it can be anything. We want to paint the green and red squares so that we see what is behind the opening(s)''' import matplotlib.pyplot as plt fig, ax = plt.subplots(figsize=(6, 6)) # This is to test if a well ordered polygon with slits (to define holes) can be rendered quad_small = [(-0.2, -0.2), (-0.2, 0.2), (0.2, 0.2), (0.2, -0.2), (-0.2, -0.2)] quad1x1 = [(-1, 1.), (-1, -1.), (1, -1.), (1., 1.), (-1, 1.)] #Fill quad1x1 with green x11 = [coord[0] for coord in quad1x1] y11 = [coord[1] for coord in quad1x1] plt.fill(x11, y11, facecolor='green', zorder=5) '''Now make one or more holes, possibly overlapping holes, NOTE: if we use clipping to define the holes, Matplotlib sets the same zorder over all the clippped areas which was used. Also clipping does not work well with overlapping small squares. Would only work with nonoverlapping squares.''' xsq = [coord[0] for coord in quad_small] ysq = [coord[1] for coord in quad_small] plt.fill(xsq, ysq, facecolor='white', zorder=5) xsq = [coord[0]+0.2 for coord in quad_small] ysq = [coord[1]+0.2 for coord in quad_small] plt.fill(xsq, ysq, facecolor='white', zorder=5) '''At this point green and white openings have the same zorder=5. We would need a call to change the zorder of all the 'white' pixels to a lower value, say 3''' '''Now we want to render another polygon (red) with holes, but ONLY on areas not covered by the previous rendering, we use a lower zorder so that we do not paint on the green part''' x11 = [coord[0]+0.3 for coord in quad1x1] y11 = [coord[1]+0.3 for coord in quad1x1] plt.fill(x11, y11, facecolor='red', zorder=4) xsq = [coord[0]+0.3 for coord in quad_small] ysq = [coord[1]+0.3 for coord in quad_small] plt.fill(xsq, ysq, facecolor='white', zorder=4) xsq = [coord[0]+0.5 for coord in quad_small] ysq = [coord[1]+0.5 for coord in quad_small] plt.fill(xsq, ysq, facecolor='white', zorder=4) '''The hole (white area) of the green square is not painted in red because the zorder of the white area is higher''' plt.show() Schlumberger-Private

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ANN: mplcairo 0.2 release
by Antony Lee Sept. 23, 2019

Sept. 23, 2019

Dear all, I am pleased to announce the release of mplcairo 0.2. mplcairo is a Matplotlib backend based on the well-known cairo library, supporting output to both raster (including interactively) and vector formats. In other words, it provides the functionality of Matplotlib's {,qt5,gtk3,wx,tk,macos}{agg,cairo}, pdf, ps, and svg backends. Per Matplotlib's standard API, the backend can be selected by calling matplotlib.use("module://mplcairo.qt") or setting your MPLBACKEND environment variable to `module://mplcairo.qt` for Qt5, and similarly for other toolkits. mplcairo 0.2 adds support for cairo 1.17.2's high-precision floating point surfaces, simplifies the use of custom compositing operators (see `examples/operators.py`), a few other features listed in the changelog, as well as the usual bugfixes over 0.1. Enjoy, Antony Lee

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created v3.2.x branch
by Paul Ivanov Sept. 11, 2019

Sept. 11, 2019

Hi everyone, I created the 3.2.x branch and set up the bot to backport to PRs in the v3.2.0 milestone. onward and awkward, pi -- _ / \ A* \^ - ,./ _.`\\ / \ / ,--.S \/ \ / `"~,_ \ \ __o ? _ \<,_ /:\ --(_)/-(_)----.../ | \ --------------.......J Paul Ivanov https://pirsquared.org <http://pirsquared.org> | GPG/PGP key id: 0x0F3E28F7

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Reschedule weekly call
by Thomas Caswell Sept. 2, 2019

Sept. 2, 2019

Folks, Can we re-schedule the weekly call to Tuesdays 15:00 Eastern US time (UTC -05:00). This is the name time, but shifted forward a day. This would go into effect next week (2019-09-03). Tom -- Thomas Caswell tcaswell(a)gmail.com

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