Finite axis lines

[bclehmann]

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Purpose:
#1390

var x_squared = plt.AddFunction(x => x * x);

var line1 = plt.AddHorizontalLine(1);
line1.Max = 1;
line1.Color = Color.Gray;

var line2 = plt.AddVerticalLine(1);
line2.Max = 1;
line2.Color = Color.Gray;


var line3 = plt.AddHorizontalLine(4);
line3.Max = 2;
line3.Color = Color.Gray;

var line4 = plt.AddVerticalLine(2);
line4.Max = 4;
line4.Color = Color.Gray;

plt.SetAxisLimits(0, 5, 0, 5);

[bclehmann]

I think this can probably be extended to AxisSpan as well.

And I think Crosshair could mimic this look, maybe an option to disable each of the "legs" individually?

[swharden]

Thanks for getting this PR started @bclehmann!

What would you think if I replaced double? with double and defaulted it to NegativeInfinity, then used Math.Max() in Render() to compare it to the dims value?

My thinking is that MaximumInfinity describes the behavior a little more explicitly than null

If this sounds good to you I can make the change and merge it in before the next release today

PS: I posted this as a code line comment ~2 days ago but I think it got stuck in GitHub's API and was labeled "pending" that whole time so I deleted it and am re-posing as a general review comment

[bclehmann]

What would you think if I replaced double? with double and defaulted it to NegativeInfinity, then used Math.Max() in Render() to compare it to the dims value?

Sure, I used null because I find ?? easier to read than a ternary, but I think Math.Max or Math.Min is just as readable, so we might as well avoid the boxing of nullables.

PS: I posted this as a code line comment ~2 days ago but I think it got stuck in GitHub's API and was labeled "pending" that whole time so I deleted it and am re-posing as a general review comment

Huh, weird, I've never gotten that before. I have seen "pending" it it's a comment as part of a review, but that goes away as soon as I complete the review (approve, suggest changes, etc)