Improving Performace

[Snolandia]

Just wanted to start a discussion on this to keep track of what I'm finding/ trying to improve, and for suggestions/solutions.

This push started because while using the live-data sample graph, while the performance for 1 graph was ok enough for my uses,
while trying to add multiple graphs performance was significantly poorer than will meet my needs, as well as running into a weird rendering bug seemingly caused by the performance drop.

[Snolandia]

JKQTPEnhancedPainter, drawPolyLineFast

Im finding that QPainter drawPolyline has some signifigant performace issues. Just by moving to a loop and using QPainter::drawLine, Ive seen an average of 250% speed increase in drawing lines. Continuing to dig into this.

[Snolandia]

Continuing to use the same example. By only replacing drawPolylineFast, drawPolyline with the drawLines loops, and running a timing test over 1000 frames, ran several times for consistency, the results

No AA => Base: 22ms per frame. Modified: 12ms per frame
AA => Base: 83ms per frame, Modified: 19ms per frame

while overall an obviously large improvement, the difference with AA turned on is absolutely massive, and was quite unexpected. QPainter::drawPolyline must have some major underlying issue with it.