Animation of right-aligned windows is twitchy

[niello]

See GameMenu sample for example. LabelDelete is animated through the parent container resizing. At some point the parent container size is rounded so that the label position shifts one pixel right although the animation must smoothly move it to the left. This produces noticeable twitch.

Here are logs from Element::getUnclippedOuterRect_impl:

old: x:447 y:329, pos: x:447.49219, size: w:19, parent rect: l:403 r:466
old: x:447 y:329, pos: x:447.5, size: w:19, parent rect: l:402 r:466

They are obtained by inserting this code:

const auto prevPos = getUnclippedOuterRect().getCurrent().d_min;
...
if (auto label = dynamic_cast<const Window*>(this))
	if (label->getName() == "LabelDelete")// && prevPos.x < offset.x)
		Logger::getSingleton().logEvent(
			"***DBG old: " + PropertyHelper<glm::vec2>::toString(prevPos)
			+ ", pos: " + PropertyHelper<glm::vec2>::toString(offset)
			+ ", size: " + PropertyHelper<Sizef>::toString(pixel_size)
			+ ", parent rect: " + PropertyHelper<Rectf>::toString(parent_rect), LoggingLevel::Warning);

The fix might be in calculating parent-child rects without pixel alignment, and aligning only when render, but this may have unpredictable consequences. Need to think about it.

[niello]

I've found that disabling pixel alignment of problematic widgets almost solves the problem.

    if (auto wnd = d_root->getChild("InnerButtonsContainer/PopupLinesCharacters/LabelDelete"))
        wnd->setPixelAligned(false);
    if (auto wnd = d_root->getChild("InnerButtonsContainer/PopupLinesCharacters/LabelSelect"))
        wnd->setPixelAligned(false);

This produces a lot smoother animation, yet it doesn't eliminate logical twitching, and also it may work bad with texts, when the pixel alignment in not animated directions is desired. I.e. it is ok to disable horizontal pixel alignment when animate X axis, but Y must be aligned all the time, and when an animation ends, X must be aligned too. So this solution is only partial yet acceptable for basic cases.