Re: [matplotlib-devel] graphics context: use alpha value from foreground color if present

On 08/26/2011 08:21 PM, Michiel de Hoon wrote:
> Thanks! That solves the problem for me.
> Once these changes have made it into trunk, I can commit my changes to the MacOSX backend.

Done--I hit the merge button.

Eric

>
> Thanks,
> --Michiel
>
> --- On Fri, 8/26/11, Eric Firing<ef...@ha...>  wrote:
>
>> From: Eric Firing<ef...@ha...>
>> Subject: Re: [matplotlib-devel] graphics context: use alpha value from foreground color if present
>> To: mat...@li...
>> Date: Friday, August 26, 2011, 10:20 PM
>> On 08/26/2011 06:23 AM, Michiel de
>> Hoon wrote:
>>> Dear all,
>>>
>>> I am currently modifying the MacOSX backend to make
>> its interactive/non-interactive behavior consistent with the
>> other backends in matplotlib.
>>> When I was testing the backend, I found a new bug that
>> seems to be related to a recent change in backend_bases.py:
>>
>> Michiel,
>>
>> Thank you for doing this work on the MacOSX backend; sorry
>> to have
>> introduced a bug that you stumbled over.
>>
>>>
>>> https://github.com/matplotlib/matplotlib/commit/4c078ddf68cc0ecc1a5f36009a3e3a8b4921b037#lib/matplotlib/backend_bases.py
>>>
>>> After this commit, GraphicsContextBase.set_alpha has
>> no effect if alpha==None; previously it would set alpha to
>> 1.0.
>>>
>>> The bug appears here in Text.draw in text.py:
>>>
>>>            gc =
>> renderer.new_gc()
>>>
>> gc.set_foreground(self.get_color())
>>>
>> gc.set_alpha(self.get_alpha())
>>>
>>> In this code, self is a Text object, which derives
>> from the Artist class, which initializes its _alpha member
>> to None. So self.get_alpha() returns None, and gc.set_alpha
>> has no effect. The alpha value used then depends on whatever
>> was present in the gc before the call to new_gc, which is
>> backend-dependent; the MacOSX and cairo backends end up with
>> an incorrect alpha value.
>>>
>>> I guess the easiest solution is to initialize _alpha
>> in the Artist class to 1.0 instead of to None.
>>
>> See https://github.com/matplotlib/matplotlib/pull/437
>>
>> The problem was occurring because the macosx and cairo
>> backends were
>> recycling their graphics context objects instead of making
>> new
>> instances, so they were not getting initialized.  I
>> made a local fix by
>> initializing the _alpha attributes; it may be that other
>> initialization
>> is actually needed as well, and that the
>> GraphicsContextBase.__init__
>> method should be called, but I have not looked into
>> that.  The small fix
>> solves the immediate problem.
>>
>> In addition, I realized that a small change in
>> GraphicsContextBase was
>> needed to properly support backends that have their own
>> set_alpha and
>> set_foreground methods in their gc class.
>>
>> Eric
>>
>>>
>>> Thanks,
>>> --Michiel
>>
>> ------------------------------------------------------------------------------
>> EMC VNX: the world's simplest storage, starting under $10K
>> The only unified storage solution that offers unified
>> management
>> Up to 160% more powerful than alternatives and 25% more
>> efficient.
>> Guaranteed. http://p.sf.net/sfu/emc-vnx-dev2dev
>> _______________________________________________
>> Matplotlib-devel mailing list
>> Mat...@li...
>> https://lists.sourceforge.net/lists/listinfo/matplotlib-devel
>>
>
> ------------------------------------------------------------------------------
> EMC VNX: the world's simplest storage, starting under $10K
> The only unified storage solution that offers unified management
> Up to 160% more powerful than alternatives and 25% more efficient.
> Guaranteed. http://p.sf.net/sfu/emc-vnx-dev2dev
> _______________________________________________
> Matplotlib-devel mailing list
> Mat...@li...
> https://lists.sourceforge.net/lists/listinfo/matplotlib-devel