Portability | GHC with TypeFamilies and more |
---|---|

Stability | unstable |

Maintainer | stephen.tetley@gmail.com |

Font size calculation for Label's and their bounding boxes.

Calculations are based on metrics derived from Courier at 48pt. As Courier is a monospaced font, bounding boxes calculated for other font families will usually have longer width than is necessary for the printed text.

This is a deficiency of Wumpus, and limits its text handling capabilities (for example, text cannot be automatically centered). However, alternatives would need access to font metrics - this would require a font loader and add significant implementation complexity.

- type FontSize = Int
- type CharCount = Int
- courier48_width :: Num u => u
- courier48_height :: Num u => u
- courier48_numeral_height :: Num u => u
- courier48_xheight :: Num u => u
- courier48_descender_depth :: Num u => u
- courier48_ascender_height :: Num u => u
- courier48_spacer_width :: Num u => u
- widthAt48pt :: Fractional u => CharCount -> u
- textWidth :: Fractional u => FontSize -> CharCount -> u
- textHeight :: Num u => FontSize -> u
- numeralHeight :: Fractional u => FontSize -> u
- xcharHeight :: Fractional u => FontSize -> u
- descenderDepth :: Fractional u => FontSize -> u
- textBounds :: (Fractional u, Ord u) => FontSize -> Point2 u -> CharCount -> BoundingBox u

# Type synonyms

# Courier metrics at 48 point

courier48_width :: Num u => uSource

The width of a letter in Courier at 48 pt.

The value is not entirely accurate but it is satisfactory.

width = 26.0

courier48_height :: Num u => uSource

The point size of a character in Courier at 48 pt.

** Naturally the height is 48.0 **.

courier48_numeral_height :: Num u => uSource

The height of a numeral without accents, ascenders or descenders in Courier at 48 pt.

Note - the height of a numeral in Courier is slightly larger than a upper-case letter.

numeral_height = 30.0

courier48_xheight :: Num u => uSource

The height of the body of a lower-case letter (typically the letter 'x') in Courier at 48 pt.

This is also known as the "body height".

xheight = 20.0

courier48_descender_depth :: Num u => uSource

The depth of a descender in Courier at 48 pt.

descender_depth = 9.0

courier48_ascender_height :: Num u => uSource

The depth of an ascender in Courier at 48 pt.

ascender_height = 10.0

Note - for Courier point size is not the sum of descender, ascender and xheight and lower-case letters with ascenders are slightly taller than upper-case letters:

descender_depth + xheight + ascender_height /= point_size

xheight + ascender_height /= cap_height

xheight + ascender_height == numeral_height

courier48_spacer_width :: Num u => uSource

The spacing between letters printed directly with PostScript's show command for Courier at 48 pt.

The value is not entirely accurate but it is satisfactory for bounding box calculations.

spacer_width = 3.0

# Metrics calculation

widthAt48pt :: Fractional u => CharCount -> uSource

Width of the supplied string when printed at 48pt.

textWidth :: Fractional u => FontSize -> CharCount -> uSource

Text width at `sz`

point size of the string `s`

. All
characters are counted literally - special chars may cause
problems (this a current deficiency of Wumpus).

textHeight :: Num u => FontSize -> uSource

Text height is just identity/double-coercion of the Point size.
i.e. `18 == 18.0`

. The *size* of a font is the maximum height:

numeralHeight :: Fractional u => FontSize -> uSource

Approximate the height of a numeral using metrics derived from the Courier monospaced font.

xcharHeight :: Fractional u => FontSize -> uSource

Approximate the height of the lower-case char 'x' using metrics derived from the Courier monospaced font.

descenderDepth :: Fractional u => FontSize -> uSource

Approximate the descender depth for font size `sz`

using
metrics derived from the Courier monospaced font.

textBounds :: (Fractional u, Ord u) => FontSize -> Point2 u -> CharCount -> BoundingBox uSource

Find the bounding box for the character count at the supplied font-size.

The supplied point represents the bottom left corner of the
a regular upper-case letter (that is without descenders).
The bounding box will always be *dropped* to accommodate
ascenders - no interpretation of the string takes place to
see if it actually contains ascenders or descenders.

The metrics used are derived from Courier - a monospaced font. For variable width fonts the calculated bounding box will usually be too long.