Question

I am rendering an interpolation curve thusly:

e.Graphics.DrawLines(new Pen(Color.Red), _interpolationPoints.ToArray());

which sometimes throws an OverflowException.

Examination of the _interpolationPoints array shows some very large values in scientific notation e.g. {X = 0.0 Y = -1.985174E+10}

I suspect that Y = -1.985174E+10 is a value that GDI+ cannot handle. That’s fine but what are the max/min X and Y values into which I can draw and so constrain the data (and warn the user) rather than catching the overflow exception during paint? Are the limits documented?

For example, I would like to do something like this:

if (yVal < float.MinValue || yval > float.MaxValue) 
      throw new OverflowException("Interpolation value too large to be rendered.");

during the population of the _interpolationPoints array and stop the process. (float mix/max does not work btw. i still get the exception.)

Answer 1

OK, I needed to know so I tested incrementally and came up with these limits:

positive:    1,073,741,951
negative:   -1,073,741,760

The code I used looked something like this:

int lastGoodVal = 0;
for (int i = -1073000000; i > -1073832999; i -= 1)
{
    g.DrawLine(Pens.Blue, new Point(0,0), new Point(0, i));
    lastGoodVal = i;
}

The loop above was the final test, stepping by 1, through a range of negative values established by earlier tests. As you can see, lastGoodVal holds the last successful painting iteration and therefore the real limit which I’ll use as a constant.

I tried to correlate these numbers to a value in the .NET primitives but couldn’t. Each limit is close to the value of 2^30 but is not exactly on it. Any other insight would be much appreciated.

I also only tested with the DrawLine method. It’s possible that different limits exist for other functions in the API but I have not had a chance to explore that yet.

Also, after finishing this experiment and then Googling for the value 1073741951 I came across this article which correlates my findings. I also found this in a Mono code archive of some sort which mentions a near, though not exact correlation to float limits.