= Glyph bearing
A \b[glyph bearing] is a signed offset locating a <glyph>'s ink relative to the reference used for layout. In a simple horizontal metric, the <left side bearing> measures the offset from the <pen position> to the left ink edge, and the <right side bearing> measures the remaining distance from the right ink edge to the advance endpoint.<Glyph Metrics in the FreeType documentation>[§3: bearings and advances]{ref}
Put the origin at $x=0$, the <glyph advance> at $a$, and the ink edges at $x_L,x_R$. Then
$$
\boxed{\mathrm{lsb}=x_L,\qquad w=x_R-x_L,\qquad
\mathrm{rsb}=a-x_R,\qquad a=\mathrm{lsb}+w+\mathrm{rsb}.}
$$
For $x_L=-2$, $x_R=9$ and $a=12$, the bearings are $-2$ and 3, while the ink width is 11. The negative left bearing records an overhang across the origin. The next nominal <pen position> remains at $x=12$.
\Image[/glyph-bearing-geometry.png]
{title=Ink bounds, side bearings and <glyph advance>}
{description=Original horizontal schematic with an invented outline: left ink edge -2, right ink edge 9, advance 12. The plotted shape is not copied from a font. Horizontal measurements are in consistent arbitrary units.}
These are measurements of a default horizontal arrangement. Subsequent <glyph positioning> and <kerning> can change the rendered relationship between neighbouring <glyphs>. The reference point and axes must also be checked when applying bearing conventions to vertical layout.
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