Tweak behaviour of NanoWidget as subwidget of another NanoWidget

[pdesaulniers]

This would fix the weird behavior I've described in #68.

I really don't know if this is a proper fix, but it works with Wolf Shaper and the rectangles example I've shown in the issue.

It makes the subwidgets pass through this OpenGL code, which sets the correct viewport:

DPF/dgl/src/WidgetPrivateData.hpp

Lines 81 to 88 in 6d35b69

	else if (needsScaling)
	{
	// limit viewport to widget bounds
	glViewport(absolutePos.getX(),
	static_cast<int>(height - self->getHeight()) - absolutePos.getY(),
	static_cast<GLsizei>(self->getWidth()),
	static_cast<GLsizei>(self->getHeight()));
	}

So, calling rect(0, 0, getWidth(), getHeight()); should draw a rectangle equal to the widget's viewport.

Also, in onNanoDisplay(), you can freely use NanoVG's translate(), reset(), etc. It doesn't seem to affect the OpenGL viewport.

[falkTX]

I rather not do this until I am 100% sure it is the right thing.
Sorry it is taking long.

[pdesaulniers]

No worries, take your time. I'm not sure this is OK either.

[pdesaulniers]

I don't understand why skipDisplay is needed. Why not draw all widgets directly, without special treatment for subwidgets?

In pseudocode:

for each widget in window:
    if widget is visible:
        setup the glViewport
        call widget->onDisplay()

onDisplay would just draw the widget itself, not the subwidgets.

[pdesaulniers]

The pugl-upstream-v2 branch appears to fix my original issue. Closing this PR, as the code is probably not relevant anymore.