Re: [Matplotlib-users] Possible bug with contour, alpha blending and vector output
Moving to the devel list, since this concerns an internal API of matplotlib. Thanks to Sourav for reporting this and to Eric for sending the note to me. Eric Firing efir...@hawaii.edu writes: Sourav K. Mandal wrote: I have a simple problem: when outputting to PDF or SVG, alpha blending does not work for the lines drawn by contour. However, alpha blending does work for the regions given by contourf. You are right, this is a real bug, verified in svn. The contour function creates a LineCollection, which gets drawn via draw_path_collection, which the pdf backend inherits from backend_bases. The default draw_path_collection (or _iter_collection really) communicates the alpha of the *face color* only by setting the alpha attribute of the GraphicsContext: if rgbFace is not None and len(rgbFace)==4: gc0.set_alpha(rgbFace[-1]) rgbFace = rgbFace[:3] The alpha of the line only gets communicated via the fourth component of the rgb attribute of the GraphicsContext, and currently the pdf backend doesn't do anything with it. I think this could be resolved in a number of ways, none of which is obviously the perfect solution: 1. Add a check in _iter_collection for gc0._rgb having an alpha component, similar to the current check for rgbFace, and set the alpha attribute from that one too. (What if both rgbFace and gc0._rgb have an alpha component?) 2. Make each backend's GraphicsContext set the alpha attribute from the color. (If the alpha attribute is already set, how should they be combined? Multiply, take the minimum, or what?) 3. Either get rid of the alpha attribute on the GraphicsContext and use only rgba tuples within backends, or turn it into two attributes (e.g. alphaFace and alphaStroke). (What to do with the frontend's single alpha attribute?) By the way, I have never really understood why rgbFace is given separately from the GraphicsContext. Is this just an evolutionary remnant or is there a deeper meaning for it? -- Jouni K. Seppänen http://www.iki.fi/jks -- The Planet: dedicated and managed hosting, cloud storage, colocation Stay online with enterprise data centers and the best network in the business Choose flexible plans and management services without long-term contracts Personal 24x7 support from experience hosting pros just a phone call away. http://p.sf.net/sfu/theplanet-com ___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
[Matplotlib-users] Possible bug with contour, alpha blending and vector output
Hello, I am using Matplotlib version 0.99.1.1. I have a simple problem: when outputting to PDF or SVG, alpha blending does not work for the lines drawn by contour. However, alpha blending does work for the regions given by contourf. Both work when outputting to PNG. My Python script (and data file) and example output (PDF, SVG, PNG) are posted here: http://panic.berkeley.edu/~smandal/ Thank you! Regards, Sourav -- The Planet: dedicated and managed hosting, cloud storage, colocation Stay online with enterprise data centers and the best network in the business Choose flexible plans and management services without long-term contracts Personal 24x7 support from experience hosting pros just a phone call away. http://p.sf.net/sfu/theplanet-com ___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
Re: [Matplotlib-users] Possible bug with contour, alpha blending and vector output
Sourav K. Mandal wrote: Hello, I am using Matplotlib version 0.99.1.1. I have a simple problem: when outputting to PDF or SVG, alpha blending does not work for the lines drawn by contour. However, alpha blending does work for the regions given by contourf. You are right, this is a real bug, verified in svn. Since the agg backend works correctly and the pdf and svg backends do not, it appears to be essentially a bug in those backends. I am calling this to Jouni's attention, since he is the pdf backend expert; but in case neither he nor anyone else can get to it right away, if you have not seen any other response within a day, please file a bug report on the tracker so this doesn't get lost. If you do so, please use a simple and completely self-contained script to illustrate the problem. http://sourceforge.net/tracker/?group_id=80706 Thank you. Eric Both work when outputting to PNG. My Python script (and data file) and example output (PDF, SVG, PNG) are posted here: http://panic.berkeley.edu/~smandal/ Thank you! Regards, Sourav -- The Planet: dedicated and managed hosting, cloud storage, colocation Stay online with enterprise data centers and the best network in the business Choose flexible plans and management services without long-term contracts Personal 24x7 support from experience hosting pros just a phone call away. http://p.sf.net/sfu/theplanet-com ___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users -- The Planet: dedicated and managed hosting, cloud storage, colocation Stay online with enterprise data centers and the best network in the business Choose flexible plans and management services without long-term contracts Personal 24x7 support from experience hosting pros just a phone call away. http://p.sf.net/sfu/theplanet-com ___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
