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 :: PtSize
- courier48_height :: PtSize
- courier48_numeral_height :: PtSize
- courier48_xheight :: PtSize
- courier48_descender_depth :: PtSize
- courier48_ascender_height :: PtSize
- courier48_spacer_width :: PtSize
- widthAt48pt :: CharCount -> PtSize
- charWidth :: FontSize -> PtSize
- textWidth :: FontSize -> CharCount -> PtSize
- textHeight :: FontSize -> PtSize
- numeralHeight :: FontSize -> PtSize
- xcharHeight :: FontSize -> PtSize
- descenderDepth :: FontSize -> PtSize
- textBounds :: (Fractional u, Ord u, FromPtSize u) => FontSize -> Point2 u -> CharCount -> BoundingBox u
Courier metrics at 48 point
The width of a letter in Courier at 48 pt.
The value is not entirely accurate but it is satisfactory.
width = 26.0
The point size of a character in Courier at 48 pt.
** Naturally the height is 48.0 **.
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
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
The depth of a descender in Courier at 48 pt.
descender_depth = 9.0
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
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
Width of the supplied string when printed at 48pt.
(i.e. n chars + (n-1) spacers)
Approximate the width of a monospace character using metrics derived from the Courier font.
Text width at
sz point size of the string
characters are counted literally - special chars may cause
problems (this a current deficiency of Wumpus).
Text height is just identity/double-coercion of the Point size.
18 == 18.0. The size of a font is the maximum height:
Approximate the height of a numeral using metrics derived from the Courier monospaced font.
Approximate the height of the lower-case char 'x' using metrics derived from the Courier monospaced font.
Approximate the descender depth for font size
metrics derived from the Courier monospaced font.
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.