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

[Phil R. <p.d...@gm...>]

On 3 October 2017 at 18:00, Alan W. Irwin <ir...@be...> wrote:
> 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).

No, sadly it does not. I can only access functions that are in wxDC.
wxGraphicsContext is neither a parent nor a child class to wxDC, it is
totally unrelated.
The wxGCDC class is a child of wxDC. It takes wxDC commands and then
calls equivalent wxGraphicsContext commands. This is how we make use
of the wxGraphicsContexts rendering.