Confusing Font/Text Structs

[siefkenj]

Looking through the code, there seems to be a lot of different font/text structs. Some can be converted into one another with .into() and others cannot. Some need a reference to the backend. In particular TextStyle vs TextStyleBuilder confuse me.

Can you explain the logic around so many different font objects? Can it be simplified?

[38]

Hi, the font object is a little bit tricky. Please let me explain the general out-line at this point.

For API users, what they want to use is any types that impls IntoTextStyle. This allows the API flexible, as you can either pass a string as font name, or a tuple of (font_name, font_size), etc. Another additional note to this type: We support relative sizing, for example ("serif", (10).percent_height()) will turns into a text style that depends on its parent's height.

And TextStyle is actual struct that describes style information about a text. Currently it's a collection of font, color and the anchor position. P.S. more data may be added in the future.

The type FontDesc is what we used to describe a font. This struct is a little bit trickier as Plotters allows different font implementations. For example, Plotters use font-kit backed font implementation by default. While for WASM, Plotters use the web-browser. Also, if we want a minimize the dependency, we can opt-in the mocked font, which only estimate the font size. (This is what happening if you use SVG backend and disable default features - this is how criterion is using plotters.)

I don't think we have a TextStyleBuilder type.

Let me know if you have any thoughts.

Also, thanks for the layout PR!

[aleb]

There is a TextStyleBuilder, see https://docs.rs/plotters/latest/plotters/style/trait.IntoTextStyle.html

It can be confusing when typing by mistake with_color instead of color:

let text_style = plotters::style::text::TextStyle::from(("sans-serif", 20).into_font())
    .with_color(&BLUE);

..because you expect a TextStyle but you get a TextStyleBuilder which cannot be used as is, for example:

201 | plotters::element::text::Text::new("my text", (0, 0), text_style);
    | ----------------------------------                    ^^^^^^^^^^ the trait `std::convert::From<&plotters::style::text::TextStyleBuilder<'_, plotters::style::TextStyle<'_>>>` is not implemented for `plotters::style::FontDesc<'_>`
    | |
    | required by a bound introduced by this call

..then you try to use into_text_style(P) which requires a parameter which in the examples is the drawing_area object! When processing a large number of drawing_areas one would think to create a TextStyle object and reuse it but on this path you might think it's not possible. It could have been simpler to accept only a pixels value instead of a SizeDesc; one can very easily convert the SizeDesc to a pixels value manually. Quite a few of the into_text_style implementations ignore the parameter.