Documentation
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Overview ¶
Package fontmetrics answers "how wide is this string" using nothing but the standard library.
It exists for the built-in SVG backend. That backend emits <text> elements and lets the viewer shape them, but refract's layout still has to size margins, space ticks and detect label collisions before the SVG is written — and that needs metrics. So this package reads the advance widths out of a TrueType/OpenType file (head, hhea, hmtx, cmap) and nothing else: no shaping, no GSUB/GPOS, no rasterization.
Accuracy ¶
Advances are per-glyph sums with no kerning and no substitution. For Latin chart labels — which is what ticks, axis titles and legends are — that is within a fraction of a pixel of a shaped result. For scripts that require shaping it is an approximation, and refract accepts that on the SVG path: the viewer shapes the text anyway, so exact agreement was never available. The gg backend measures with the same shaper it draws with and is exact.
Index ¶
Constants ¶
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Variables ¶
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Functions ¶
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Types ¶
type Face ¶
type Face interface {
// Advance returns the total advance width of s, in device units.
Advance(s string) float64
// Ascent returns the distance from the baseline to the top of the font
// box, positive, in device units.
Ascent() float64
// Descent returns the distance from the baseline down to the bottom of the
// font box, positive, in device units.
Descent() float64
}
Face measures text at a specific size.
func Builtin ¶
Builtin returns a Face over the built-in metrics at the given size.
weight and italic are accepted so callers do not have to special-case the fallback, but only weight is honoured, and crudely: bold text is treated as 4% wider, which is about right for the sans faces this table approximates. Synthetic obliquing does not change advances at all.
type Font ¶
type Font struct {
// contains filtered or unexported fields
}
Font is a parsed font's size-independent metrics.
func Parse ¶
Parse reads the metric tables out of a TrueType or OpenType font.
It reads exactly four tables — head for unitsPerEm, hhea for the vertical metrics and the hmtx entry count, hmtx for advances, cmap for the rune-to-glyph mapping — and ignores everything else in the file, including the outlines. Parsing is bounds-checked throughout: font files arrive from users and must not be able to panic a render.
Source Files