Issue was in GP draw code: line thickness was not initiated properly (and a null one makes OGL draw a unity-width line). Also tweaked threshold (when to start a new, width-different OGL linestrip), to make it inversaly proportional to thickness (so that now, it's 0.2 for a thickness of 1, 0.1 for a thickness of 2, etc.), avoids too big steps when using large thickness.