Portability | GHC |
---|---|
Stability | unstable |
Maintainer | stephen.tetley@gmail.com |
Wumpus.Core.FontSize
Description
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, applying these metrics to other font families will usually produce over-estimates (bounding boxes will be longer than the true visual length of the text).
This is a deficiency of Wumpus, and limits its text handling capabilities - for example, text cannot be reliably centered or right aligned as its true length is not known. However, more powerful alternatives would need access to the metrics embedded within font files. 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
- spacerWidth :: FontSize -> PtSize
- textWidth :: FontSize -> CharCount -> PtSize
- textHeight :: FontSize -> PtSize
- numeralHeight :: FontSize -> PtSize
- xcharHeight :: FontSize -> PtSize
- descenderDepth :: FontSize -> PtSize
- textBounds :: (Num u, Ord u, FromPtSize u) => FontSize -> Point2 u -> String -> BoundingBox u
- textBoundsEnc :: (Num u, Ord u, FromPtSize u) => FontSize -> Point2 u -> EncodedText -> BoundingBox u
- charCount :: String -> CharCount
Type synonyms
Courier metrics at 48 point
courier48_width :: PtSizeSource
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 :: PtSizeSource
The point size of a character in Courier at 48 pt.
** Naturally the height is 48.0 **.
courier48_numeral_height :: PtSizeSource
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 :: PtSizeSource
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 :: PtSizeSource
The depth of a descender in Courier at 48 pt.
descender_depth = 9.0
courier48_ascender_height :: PtSizeSource
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 :: PtSizeSource
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 :: CharCount -> PtSizeSource
Width of the supplied string when printed at 48pt (i.e. n chars + (n-1) spacers).
Use charCount
to calculate the CharCount
.
charWidth :: FontSize -> PtSizeSource
Approximate the width of a monospace character using metrics derived from the Courier font.
spacerWidth :: FontSize -> PtSizeSource
Approximate the width of a spacer between monospace characters using metrics derived from the Courier font.
textWidth :: FontSize -> CharCount -> PtSizeSource
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 :: FontSize -> PtSizeSource
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 :: FontSize -> PtSizeSource
Approximate the height of a numeral using metrics derived from the Courier monospaced font.
xcharHeight :: FontSize -> PtSizeSource
Approximate the height of the lower-case char 'x' using metrics derived from the Courier monospaced font.
descenderDepth :: FontSize -> PtSizeSource
Approximate the descender depth for font size sz
using
metrics derived from the Courier monospaced font.
textBounds :: (Num u, Ord u, FromPtSize u) => FontSize -> Point2 u -> String -> BoundingBox uSource
textBounds
: font_size * baseline_left * text -> BBox
Find the bounding box for the character count at the supplied font-size.
The supplied point represents the baseline 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.
textBoundsEnc :: (Num u, Ord u, FromPtSize u) => FontSize -> Point2 u -> EncodedText -> BoundingBox uSource
textBoundsEnc
: font_size * baseline_left * encoded_text -> BBox
Version of textBounds for EncodedText.
Note this function is hidded by the top-level module
Wumpus.Core
.