Using Qt To Draw the Graph of Sin(x)

I am doing a very similar thing currently with painting the bode sweep of a parametric EQ (a long line with multiple sweeping curves). The way I'm doing it (pseudo style):

qreal yCoords[GRAPH_WIDTH];
...
QPainter Painter(this);
Painter.setRenderHint(QPainter::Antialiasing, true);
//Painter.setRenderHint(QPainter::HighQualityAntialiasing, true); //opengl specific
for(int xCoord = 0; xCoord < GRAPH_WIDTH; x++)
  Path.lineTo(QPointF(xCoord, yCoord[xCoord]));
...
Painter.drawPath(Path);

The combination of the calls to setRenderHint and drawing lines with QPointF (i.e. two qreal) rather than QPoint (two int) makes the line very smooth.

We're using this on an SBC running Ubuntu and getting redraw timings (including all of the complex math to get the points in the first place) of ~80ms for a 600x300px graph. Initial tests show that enabling opengl rendering reduces this to ~8ms (clearly the processor intensive task is the painting with antialiasing), so if you can do that, I think this solution will work for you.

QCustomPlot is a free and easy to use class that can be found online. It may be better for what you are looking to do.