Vertically centered text appears too low

[paulkernfeld]

I created an example here that illustrates. I would expect that the base of the text and the top of a capital letter are each the same distance from the vertical border of the window, but instead I observe that the base of the text is closer to the bottom of the window than the top of the capital is to the top of the window.

[hecrj]

glyph-brush's vertical align doesn't align a set of glyphs in particular. It think it only uses the font properties, so it accounts for accents and other kind of symbols on top of some glyphs.

This is desirable for most use cases when you have dynamic text because it avoids awkward jumps. I am guessing the small difference that is still left depends entirely on the font.

If you want to completely center the produced glyphs, you should be able to use GlyphBrush::pixel_bounds (from the GlyphCruncher implementation) and then set the screen_position appropriately when queueing.

[hecrj]

Something like this:

let mut section = Section {
    text: "gŽ",
    color: [0.0, 0.0, 0.0, 1.0],
    scale: Scale::uniform(scale as f32),
    bounds: (size.width as f32, size.height as f32),
    ..Section::default()
};

let pixel_bounds =
    glyph_brush.pixel_bounds(section).expect("Pixel bounds");

section.screen_position = (
    size.width as f32 * 0.5 - pixel_bounds.min.x as f32 * 0.5,
    size.height as f32 * 0.5 - pixel_bounds.min.y as f32 * 0.5,
);

section.layout = Layout::default_single_line()
    .h_align(HorizontalAlign::Center)
    .v_align(VerticalAlign::Center);

glyph_brush.queue(section);

Produces:

It doesn't seem to be entirely centered still (?).

[hecrj]

Also, I am sure we could implement our own GlyphPositioner to do this directly without using pixel_bounds.

[paulkernfeld]

I was also imagining a centering strategy that did not depend dynamically on the particular glyphs.

Maybe it's wrong to approach this with the expectation that the baseline of the text and the top of a capital letter are perfectly equidistant from the edges; I'm not an expert in text layout. Trying out a bunch of different fonts in a text box in Google Docs, the vertical alignment seems to depend a bit on the selected typeface.

Overall I think it might make sense to close this issue, since it seems like wgpu_glyph is probably handling vertical centering in a good wya.

[hecrj]

The built-in glyph-brush glyph positioner uses rusttype::VMetrics, which seems to talk about highest/lowest glyph points, to align lines.

I am not sure if fonts provide enough information to perform the alignment you describe, but rusttype doesn't seem to expose it.