DistanceGrid.ScaledPoint

DistanceGrid has the two payload-free values ScaledPoint() and MilliPoint(). They are distinct selectors and have no numeric conversion or ambient state.

Public physical inputs and outputs remain Length<Pt> under either selector. A grid selects internal quantization and does not reinterpret an integer or change a public unit marker.

ScaledPoint uses the signed scaled-point integer stored in each physical length. MilliPoint converts each input through Length<Pt>.toMilliPoints with nearest-even rounding.

Quantize each input once at the computation boundary. Resolve a relative length against its explicit font size before this conversion. Accumulation uses the resulting integers.

Return a computed distance through fromScaledPoints for ScaledPoint or fromMilliPoints for MilliPoint. The shared constructor range and rounding rules apply at this output boundary.

Grid conversion accepts signed lengths. Each grid computation applies its sign requirements after quantization. A positive point target that becomes zero millipoints fails a positive-target requirement. Font validation occurs during resolve before grid conversion.

FixedPoint requires MilliPoint. A paragraph that selects FixedPoint with ScaledPoint returns Err containing TypesetError.InvalidPolicy. KnuthPlass accepts either grid.

Selecting a grid and converting lengths perform no I/O and do not mutate their inputs. Ordinary receiver and argument evaluation happens once before conversion. Input evaluation failures propagate before the operation begins.

A millipoint round trip can change the stored scaled-point value. For example, 4096 scaled points become 62 millipoints and then 4063 scaled points.