XY graph response slows with dashed plot

Question

I have an xy graph displaying multiple plots. I find that if at least one of the plots uses a dashed line as the line type, and that this plot has zero values displayed, then the response of the graph slows significantly. Redraws seem to take 5 to 10 times longer and cpu utilization goes way up. If I scroll the plot such that the zero values go past the endpoint of the x-axis, then the normal response returns. The effect gets worse with the number of dashed plots containing zero values, but seems independent of the number of zero values. Has anybody else seen this?

Answer 1

Since you asked so many good questions, I went back and took a harder look at the situation and I think I figured it out. I am capturing and displaying instrument data continuously as a function of time. I feed my chart with large pre-initialized (with zeros) arrays that are incrementally filled with real data from the last element forward, so that the plot line does not zoom off to the right from the last point. The x-axis is date/time. The tradeoff then is that the data to the left starts at date=0 (until the array fills). The issue is not actually that I am displaying y-values of zero as I thought at first, but that if the window on the time axis is such that the first real data point is displayed, then the plot line extends from this value left to time=0, which is a long way. Labview needs to actually compute this line to properly display the line segment from 0,0 to the first data point, but only if the first point is displayed. I think Labview has a quick method of doing this for a solid line, but that for a dashed line, it needs to compute each little dash segment and it bogs down. As it turns out, this situation will happen very seldom and I can ignore the whole issue. Thanks for the help -