Plots missing text elements when generated on AWS Lambda

[lasooch]

I'm trying to generate plots in AWS Lambda and running into an issue whereby the textual elements of the plots do not get displayed. I suspect this might be a font issue, but I'm not positive - I also think I've set up my fonts correctly, but alas. Has anyone else ran into this problem before?

I don't get this issue when rendering the plot locally (on a Windows PC).

What I expect:

What I get:

Relevant plot setup code (identical across my local setup and Lambda):

var plot = new Plot();
plot.Axes.DateTimeTicksBottom();
plot.Legend.Alignment = Alignment.LowerLeft;
plot.Legend.FontName = "Segoe UI"; // also tried "Segoe UI.ttf"

var scatter = plot.Add.Scatter(data);
scatter.LegendText = $"P95 price";

var line = plot.Add.Line(avgStartCoordinates, avgEndCoordinates);
line.LinePattern = LinePattern.Dashed;
line.LegendText = "30d average";

fonts.conf:

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>
  <dir>/var/task/Fonts/</dir>
  <cachedir>/tmp/fonts-cache/</cachedir>
  <config></config>
</fontconfig>

Fonts in the Fonts folder within the project folder (Segoe UI.ttf, Segoe UI Bold.ttf, Segoe UI Italic.ttf, Segoe UI Bold Italic.ttf).

.csproj contains the relevant file copy config:

    <None Update="Fonts/Segoe UI.ttf">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </None>
    <None Update="Fonts/Segoe UI Bold.ttf">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </None>
    <None Update="Fonts/Segoe UI Italic.ttf">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </None>
    <None Update="Fonts/Segoe UI Bold Italic.ttf">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </None>
    <None Update="fonts.conf">
      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </None>

Not sure what's missing. Or is it perhaps not related to fonts at all and instead some other issue?

[swharden]

Thanks for sharing this! I'm not sure yet what the issue is... seems related to mono/SkiaSharp#2827

[lasooch]

Thanks @swharden - that does look like it would help and does seem to confirm my theory that it's fonts-related.

I think a workaround might by possible by creating a container image (and installing fontmanager) instead of just a dotnet package upload for the lambda, but I'd honestly prefer to avoid that if not necessary.

Can you think of a possible workaround using ScottPlot as is, or would this require a code change? I can't see an obvious way to do this (since FontName is just a string) but I'm also new to using ScottPlot.

[swharden]

since FontName is just a string

I think anything that has a LabelStyle has a LabelStyle.SetTypeface() to can call to inject a custom typeface. It's a new feature from ScottPlot 5.0.33 #3722. Hopefully this is the last missing piece to help you find a solution!

[swharden]

Actually it may not be in 5.0.33 (I'm struggling to figure out what version it was added in) but it will be in the next release for sure. An alternative is to set FontFile and give it a .ttf path #3722 (comment)

[lasooch]

@swharden First of all, thank you very much for your help. I really appreciate it. There's still one missing piece though 😓

I'm on 5.0.34 and I can definitely see LabelStyle.SetTypeface().

I've only achieved moderate success with it. It worked for the axes:

plot.Axes.Left.TickLabelStyle.SetTypeface(font);
plot.Axes.Bottom.TickLabelStyle.SetTypeface(font);

But I haven't been as successful with the legend. I attempted to set it both when I create the scatter/line as well as in the plot's legend (and also both at the same time):

var scatter = plot.Add.Scatter(data);
scatter.LegendText = $"{fuelType} price";
scatter.LegendItems.First().LabelStyle.SetTypeface(font);

var line = plot.Add.Line(avgStartCoordinates, avgEndCoordinates);
line.LinePattern = LinePattern.Dashed;
line.LegendText = "30d average";
line.LegendItems.First().LabelStyle.SetTypeface(font);

plot.Legend.Alignment = Alignment.LowerLeft;
// could rewrite this nicer but I'm just prototyping this to make it work
plot.Legend.GetItems().First().LabelStyle.SetTypeface(font);
plot.Legend.GetItems().Last().LabelStyle.SetTypeface(font);

But neither seems to do what I expect it to do - the legend remains textless:

Is this behaviour expected? Am I doing something wrong? It appears neither Plot or Legend themselves have a LabelStyle.

I haven't yet tried using FontFile - I might give that a shot tomorrow.

[swharden]

Hi @lasooch, thanks for reporting this! I think the legend is accidentally resetting the manual typeface. I created issue #3830 to track adding a fix. I'm happy to see that a solution to the core problem has been found! I'll try to get this legend fix into the next release 👍

[lasooch]

@swharden wonderful - I'll keep my eyes peeled! Thanks so much again.