Breaking Changes in gonum.org/v1/plot Package

gonum.org/v1/plot, one of the graph plotting packages, has been updated to v0.9.0. It seems to include breaking changes, so I'm making a note of them here.

Return value of the plot.New function

In the plot.New() function used to create a plot.Plot instance, the previous version returned an error as well, like this:

p, err := plot.New()

However, in v0.9.0, it no longer returns an error:

p := plot.New()

Well, I suppose it's fine since it makes things a little bit easier by removing the need for error handling.

Changes to default fonts and font specification

Previously, fonts were specified as strings, like this:

plot.DefaultFont = "Helvetica"
plotter.DefaultFont = "Helvetica"

It seems the font control part has been completely rebuilt; not only has the method of specifying fonts changed, but the fonts themselves have been replaced. Specifically, you now specify them like this:

plot.DefaultFont = font.Font{
    Typeface: "Liberation",
    Variant:  "Sans",
}
plotter.DefaultFont = plot.DefaultFont

The fonts that gonum.org/v1/plot pre-caches and allows you to specify are as follows:

Typeface	Variant	Style	Weight
"Liberation"	"Serif"	font.StyleNormal	font.WeightNormal
"Liberation"	"Serif"	font.StyleNormal	font.WeightBold
"Liberation"	"Serif"	font.StyleItalic	font.WeightNormal
"Liberation"	"Serif"	font.StyleItalic	font.WeightBold
"Liberation"	"Sans"	font.StyleNormal	font.WeightNormal
"Liberation"	"Sans"	font.StyleNormal	font.WeightBold
"Liberation"	"Sans"	font.StyleItalic	font.WeightNormal
"Liberation"	"Sans"	font.StyleItalic	font.WeightBold
"Liberation"	"Mono"	font.StyleNormal	font.WeightNormal
"Liberation"	"Mono"	font.StyleNormal	font.WeightBold
"Liberation"	"Mono"	font.StyleItalic	font.WeightNormal
"Liberation"	"Mono"	font.StyleItalic	font.WeightBold

Among these, font.StyleNormal and font.WeightNormal are the default values and can be omitted. Also, if no font is specified, Liberation/Serif is set as the default. Note that the font package used for specifying Style and Weight is not gonum.org/v1/plot/font but rather golang.org/x/image/font, so be careful of package name collisions.

By the way, Liberation fonts are provided under the SIL Open Font License 1.1, and in Go, they can be controlled via the go-fonts/liberation package.

Well, it's certainly a breaking change, but with the current structure, it seems to have better affinity with the golang.org/x/image/font package, and it might make it easier to handle external font files. I won't do it because it's a hassle, though.

References

https://text.baldanders.info/golang/chart-with-golang/