#173 wxwidgets device: Need to implement native linear gradient capability

[Alan W. Irwin]

Example 30.02 has ugly looking gradient results which are due to falling back to core software emulation of a linear gradient. Instead, as discussed on list a linear gradient based on the wxwidgets library API should be used instead to get very nice results for this example (such as those from the cairo and qt devices).

[Phil Rosenberg]

wxWidgets is not capable of rendering gradients in arbitrary directions, it can only do them up, down, left or right. It can also only perform linear gradients in rectangular fill areas, not arbitrary shaped polygons as required by PLplot. Therefore it seems that for the sake of consistency we should stay with the software fallback gradient, despite the ugly results when using alpha. Instead it would be better to concentrate on sorting a nicer way to render tessalating polygons in general.

I have added this as a feature request #22 https://sourceforge.net/p/plplot/feature-requests/22/