Large Text

Drafter.Widget.Digits draws headline figures and labels at several times the height of ordinary text. This guide explains how the fonts are built and how to choose between them; the API reference lives in Drafter.Widget.Digits.Font.

Contents

• Choosing a font
• How the rasterised fonts are built
• Braille or quadrant
• FIGlet fonts and full-width layout
• Rendering as an image

Choosing a font

Fonts differ in cell footprint as much as in style, so picking one is partly a layout decision. A single headline reading can afford seven columns per character; a row of six stat panels cannot.

Every built-in font covers the same repertoire — digits, upper and lower case, and common punctuation — so swapping one for another never drops characters.

A character the font cannot draw renders as blanks of the font's widest glyph rather than raising. A display that loses one glyph is preferable to a display that crashes, and reserving the width keeps the surrounding layout intact.

How the rasterised fonts are built

:tall, :pixel and :braille are not authored as glyph art. They are rasterised at compile time from a single set of 8×16 pixel bitmaps in Drafter.Widget.Digits.Bitmap, using the pixel packings in Drafter.Widget.Digits.Raster — the same packings the chart renderers use, so a headline figure is drawn with the technique that draws the plot beside it.

Sixteen rows is the resolution braille asks for: it packs 2×4 pixels into a cell, so a four-row glyph needs sixteen pixel rows to fill it. The coarser packings downsample from those same bitmaps rather than carrying shapes of their own. Each glyph is therefore authored once and rendered at three densities, and the three fonts cannot drift apart as they are edited.

When a packing shrinks the bitmap, a shrunk pixel is lit if any pixel it covers was lit. That keeps thin strokes from disappearing at the coarser densities.

Braille or quadrant

:braille and :pixel occupy the same four by four cells. Braille carries eight pixels per cell against quadrant's four, so it resolves finer curves. Quadrant blocks survive terminal fonts with poor braille coverage. Prefer :braille unless you know the target terminal's font is weak there.

FIGlet fonts and full-width layout

Drafter.Widget.Digits.Figlet parses .flf files, which opens the catalogue to the several hundred published FIGlet fonts — a far larger repertoire than is worth authoring by hand.

Drafter lays FIGlet glyphs out full width: characters are placed side by side with no kerning or smushing. Every FIGlet font supports that layout, and it is the only layout whose spacing can be computed without interpreting a font's smushing rules, so a font can never render narrower than the space reserved for it.

Hardblanks are spaces a smushing layout must not eat. With full-width layout nothing is eaten, so they render as plain spaces.

FIGlet fonts are proportional. Drafter.Widget.Digits.Font.width/1 reports the widest glyph, which is the space a character might take; use text_width/2 to measure what a string will actually occupy.

Rendering as an image

With renderer: :graphics, a terminal that speaks the kitty, iTerm2, or sixel protocol receives the text as a transmitted picture rather than as block characters. The glyph bitmaps are scaled into a raster, so strokes land on pixel boundaries instead of cell boundaries and the text stays smooth at whatever size the layout gives it.

Scale never drops below one: the bitmaps are the finest detail available, and a raster at native size is still sharper than cells. When the box is smaller than that, the encoder's fit scales the finished picture down rather than drawing the glyphs incomplete.

Nothing here is required for Drafter.Widget.Digits to work. Where no protocol is available, Drafter.Widget.Digits.Image returns nil and the widget renders cells as usual.