Do you have a code example (sbp file) so we could test it and look where the problem does come from ?
How often and from where do you call the drawTrack routine ?
Code:
frmGPS.FLine(xStart1, yStart1 ,xEnd1, yEnd1, cRed)
frmGPS.FLine(xStart1+1, yStart1 ,xEnd1+1, yEnd1, cRed)
What is the 2nd line for ?
Is it to have thicker line ? If yes you could use the ImageLibEx, there you can define the line thickness.
In your case, if the line is almost horizontal, there will be no effect.
Best regards.