Re: [Plplot-devel] Further to your recent comment for wxwidgets gradient bug 173

[Alan W. I. <ir...@be...>]

On 2017-10-03 11:24+0100 Phil Rosenberg wrote:

> Hi Alan
> It may be possible to do as you said with a clip region and an affine
> transform. I did consider this but I am not sure if the gradient gets
> transformed or just the polygon shape. I would have to check.
>
> Regarding inheritance, you have the correct syntax. wxDC and
> wxGraphicsContext are pretty close to top level classes so only
> inherit from wxObject, which many wxWidgets classes inherit from and I
> think it basically allows conversion between classes and strings which
> specify the class name. If you look in the docs,
> e.g.http://docs.wxwidgets.org/3.1/classwx_d_c.html, there is usually
> an inheritance diagram. You have access to all the functions towards
> the base of the tree, but the magic of C++ is that the behaviour of
> some of the functions can be redefined towards the branches of a tree
> by using the virtual specifier. So for example wxDC has a virtual
> function DrawLines. So if I have a pointer to a wxDC I can always call
> myDcPointer->DrawLines(/*params*/). But then if that pointer actually
> points to an inherited class then the inherited class's version of
> that function is called, so a wxPostscriptDC would write the vector to
> the file, a wxMemoryDC would work out which pixels need shading and
> shade them, etc.

Hi Phil:

I don't claim to understand everything you have said above in your
second paragraph, but if the upshot is there are C++ ways to give us
access to all wxWidget library methods regardless of the class they
are in, then I suggest the most promising way forward (since the
documentation does not mention any limitations on this brush) is
likely to be to use wxGraphicsContext::CreateLinearGradientBrush
rather than wxDC::GradientFillLinear (which does have many documented
limitations).

(Note, this speculation jibes with the [now ancient] advice at
<http://wxwidgets.10942.n7.nabble.com/Gradient-Fill-for-Rounded-Rectangle-td28295.html>
that filling a non-rectangular area with a gradient can only be done
with wxGraphicsContext.)

To follow up my speculation above, would you be willing to check with
your wxWidgets contacts if
wxGraphicsContext::CreateLinearGradientBrush can be used in the way I
describe to paint a native gradient at any angle for any
non-rectangular area?

Alan
__________________________
Alan W. Irwin

Astronomical research affiliation with Department of Physics and Astronomy,
University of Victoria (astrowww.phys.uvic.ca).

Programming affiliations with the FreeEOS equation-of-state
implementation for stellar interiors (freeeos.sf.net); the Time
Ephemerides project (timeephem.sf.net); PLplot scientific plotting
software package (plplot.sf.net); the libLASi project
(unifont.org/lasi); the Loads of Linux Links project (loll.sf.net);
and the Linux Brochure Project (lbproject.sf.net).
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