wxPDFDocument speed up DrawLines

[doublemax]

Yes, I will do that for displaying on screen, but it has to be a thicker line in the pdf, otherwise it is too difficult to see.

I made some experiments, and with PenWidth = 4 and PenQuality set to wxPEN_QUALITY_LOW, it's still fast and with a little thicker line (but nowhere near 4 pixels).