Issue viewport navigation with lags

[Robert42]

Overview

Ok, this a quite a large Pull Request. The basic idea is, that there is now a helper class GLWidgetBase which is used as baseclass for GLWidget and GLImage to allow integrating workarounds more easily.

This pullrequests solves two issues on Linux:

1. Not responsive Viewport
2. Mouse lags back to origin

Personally I don't like the code-style of my workarounds. So maybe you want to use the workaround only as inspiraton for your final fixes.

Not responsive Viewport

There's a bug in the propertiary NVidia driver. If your GPU is too powerfull and takes less than a milisecond to draw the image, it can happen, that the whole opengl window totally freezes.
Normally the solution is to limit the framerate. But as this is not a game with a main loop, this was not an option here. Especially, as the updateGL method is called quite ofter during one event queue execution, this would slow down the application extremly.

Instead, my proposed solution is to override the updateGL method. It now doesn't paint the image immediatly, but instead queues the draw request exactly once, until the current event loop is done.

The issue however was, that for some reason, the viewport needs to be rendered multiple times before all render-effects look correct. I have no idea why, so I added a workaround to activate the queue after the main event loop is started (indicated by the first mouse movement event).

Mouse lags back to origin

This is my probosed solution for issue #33

The problem here was, that the move events on linux are split into multiple small events. For example, if you are moving the mouse by 50 pixels into the right direction, you might end up with 50 events each with offset 1 pixel, instead of one events with 50 pixels at once.

My workaround is quite ugly. It accumulates the small events into one large event, which is more easy to handle. If my workaround is too ugly for your taste, simply ignore the commit f398fdd

[kmkolasinski]

Ok, I like it. Common features of GLWidget and GLImage should be in one parent class. But I have one question: what should I call instead of updateGL() in GLImage? I'm asking because I checked your commit and with your source code version, the updateGL function does not work in GLImage class. I mean replotAllImages functions doesnt do what it shoud.

[Robert42]

actually, still updateGL is meant to be called. How can I test, whether the replotAllImages function is working?
If you want to use the old updateGL functionality to be called, there's now a new function updateGLNow(). I've made this function now public.

[kmkolasinski]

updateGLNow() - solves the problem. You can test it with e.g. "Ctrl+R" after you translate UVs.