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auto merge of #1352 : dhedlund/servo/issue_76, r=jdm,metajack
Fixes #76. Implemented the only font metric remaining to resolve issue #76 for the Linux platform. There are still some variations between Linux and OS X font metrics. Looking at values for the "Times New Roman" font, the following metrics differed by over 10%: `leading`, `x_height` and `max_advance`. It was not obvious if this would create any major difference in rendering, or whether the discrepancies would be handled in platform specific ways during the rendering process. Only `x_height` is being used by existing code. The `leading` property under Linux is still an order of magnitude off from the OS X version, but they are computed with similar calculations. Issue #1355 has been opened to further investigate the discrepancies. #### Platform comparison of font metrics for "Times New Roman" between Linux and OS X: **Au** is the raw metric values stored in the `FontMetrics` struct. **% of em** is how large that value is relative to the raw `em_size` of the font as a percentage. Linux reports the pt size differently than OS X, but this is probably because the linux platform uses hard-coded points-per-inch value (hard-coded in `src/components/util/geometry.rs`), whereas OS X uses the points-per-inch value provided by the font library. +-----------------------------------+ +-----------------------------------+ | Linux (@14.25pt, 1.33em) | | OS X (@19.35pt, 1.0em) | +------------------+------+---------+ +------------------+------+---------+ | property | Au | % of em | | property | Au | % of em | +------------------+------+---------+ +------------------+------+---------+ | underline_size | 55 | 4.82 | | underline_size | 60 | 5.17 | | underline_offset | -151 | -13.25 | | underline_offset | -120 | -10.34 | | strikeout_size | 56 | 4.91 | | strikeout_size | 0 | 0.00 | | strikeout_offset | 295 | 25.88 | | strikeout_offset | 0 | 0.00 | | leading | 541 | 47.45 | | leading | 60 | 5.17 | | x_height | 1015 | 89.04 | | x_height | 660 | 56.85 | | em_size | 1140 | 100.00 | | em_size | 1161 | 100.00 | | ascent | 1015 | 89.04 | | ascent | 893 | 76.92 | | descent | 246 | 21.58 | | descent | 203 | 17.48 | | max_advance | 1199 | 105.18 | | max_advance | 2820 | 242.89 | +------------------+------+---------+ +------------------+------+---------+ +-----------------------------------+ +-----------------------------------+ | Linux (@24pt, 1.33em) | | OS X (@32.683333pt, 1.0em) | +------------------+------+---------+ +------------------+------+---------+ | property | Au | % of em | | property | Au | % of em | +------------------+------+---------+ +------------------+------+---------+ | underline_size | 93 | 4.84 | | underline_size | 120 | 6.12 | | underline_offset | -255 | -13.28 | | underline_offset | -240 | -12.24 | | strikeout_size | 95 | 4.95 | | strikeout_size | 0 | 0.00 | | strikeout_offset | 496 | 25.83 | | strikeout_offset | 0 | 0.00 | | leading | 912 | 47.50 | | leading | 60 | 3.06 | | x_height | 1710 | 89.06 | | x_height | 1080 | 55.10 | | em_size | 1920 | 100.00 | | em_size | 1960 | 100.00 | | ascent | 1710 | 89.06 | | ascent | 1544 | 78.77 | | descent | 415 | 21.61 | | descent | 365 | 18.62 | | max_advance | 2020 | 105.21 | | max_advance | 4740 | 241.84 | +------------------+------+---------+ +------------------+------+---------+ +-----------------------------------+ +-----------------------------------+ | Linux (@45pt, 1.33em) | | OS X (@60.833333pt, 1.0em) | +------------------+------+---------+ +------------------+------+---------+ | property | Au | % of em | | property | Au | % of em | +------------------+------+---------+ +------------------+------+---------+ | underline_size | 175 | 4.86 | | underline_size | 180 | 4.93 | | underline_offset | -479 | -13.31 | | underline_offset | -480 | -13.15 | | strikeout_size | 179 | 4.97 | | strikeout_size | 0 | 0.00 | | strikeout_offset | 931 | 25.86 | | strikeout_offset | 0 | 0.00 | | leading | 1709 | 47.47 | | leading | 180 | 4.93 | | x_height | 3208 | 89.11 | | x_height | 2040 | 55.89 | | em_size | 3600 | 100.00 | | em_size | 3650 | 100.00 | | ascent | 3208 | 89.11 | | ascent | 2925 | 80.14 | | descent | 778 | 21.61 | | descent | 690 | 18.90 | | max_advance | 3788 | 105.22 | | max_advance | 8880 | 243.29 | +------------------+------+---------+ +------------------+------+---------+ +-----------------------------------+ +-----------------------------------+ | Linux (@30.75pt, 1.33em) | | OS X (@41.9pt, 1.0em) | +------------------+------+---------+ +------------------+------+---------+ | property | Au | % of em | | property | Au | % of em | +------------------+------+---------+ +------------------+------+---------+ | underline_size | 120 | 4.88 | | underline_size | 120 | 4.77 | | underline_offset | -327 | -13.29 | | underline_offset | -360 | -14.32 | | strikeout_size | 122 | 4.95 | | strikeout_size | 0 | 0.00 | | strikeout_offset | 636 | 25.85 | | strikeout_offset | 0 | 0.00 | | leading | 1168 | 47.47 | | leading | 120 | 4.77 | | x_height | 2192 | 89.11 | | x_height | 1440 | 57.27 | | em_size | 2460 | 100.00 | | em_size | 2514 | 100.00 | | ascent | 2192 | 89.11 | | ascent | 1991 | 79.20 | | descent | 532 | 21.63 | | descent | 487 | 19.37 | | max_advance | 2588 | 105.20 | | max_advance | 6120 | 243.44 | +------------------+------+---------+ +------------------+------+---------+
This commit is contained in:
bors-servo
commit
1bf28ebaf4
3 changed files with 38 additions and 6 deletions
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@ -231,6 +231,15 @@ impl FontHandleMethods for FontHandle {
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let descent = self.font_units_to_au(face.descender as float);
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let max_advance = self.font_units_to_au(face.max_advance_width as float);
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// 'leading' is supposed to be the vertical distance between two baselines,
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// reflected by the height attibute in freetype. On OS X (w/ CTFont),
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// leading represents the distance between the bottom of a line descent to
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// the top of the next line's ascent or: (line_height - ascent - descent),
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// see http://stackoverflow.com/a/5635981 for CTFont implementation.
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// Convert using a formular similar to what CTFont returns for consistency.
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let height = self.font_units_to_au(face.height as float);
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let leading = height - (ascent + descent);
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let mut strikeout_size = geometry::from_pt(0.0);
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let mut strikeout_offset = geometry::from_pt(0.0);
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let mut x_height = geometry::from_pt(0.0);
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@ -244,18 +253,21 @@ impl FontHandleMethods for FontHandle {
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}
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}
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return FontMetrics {
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let metrics = FontMetrics {
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underline_size: underline_size,
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underline_offset: underline_offset,
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strikeout_size: strikeout_size,
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strikeout_offset: strikeout_offset,
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leading: geometry::from_pt(0.0), //FIXME
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leading: leading,
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x_height: x_height,
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em_size: em_size,
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ascent: ascent,
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descent: -descent, // linux font's seem to use the opposite sign from mac
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max_advance: max_advance
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}
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};
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debug!("Font metrics (@{:f} pt): {:?}", geometry::to_pt(em_size), metrics);
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return metrics;
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}
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fn get_table_for_tag(&self, _: FontTableTag) -> Option<FontTable> {
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@ -230,6 +230,15 @@ impl FontHandleMethods for FontHandle {
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let descent = self.font_units_to_au(face.descender as f64);
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let max_advance = self.font_units_to_au(face.max_advance_width as f64);
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// 'leading' is supposed to be the vertical distance between two baselines,
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// reflected by the height attibute in freetype. On OS X (w/ CTFont),
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// leading represents the distance between the bottom of a line descent to
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// the top of the next line's ascent or: (line_height - ascent - descent),
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// see http://stackoverflow.com/a/5635981 for CTFont implementation.
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// Convert using a formular similar to what CTFont returns for consistency.
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let height = self.font_units_to_au(face.height as f64);
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let leading = height - (ascent + descent);
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let mut strikeout_size = geometry::from_pt(0.0);
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let mut strikeout_offset = geometry::from_pt(0.0);
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let mut x_height = geometry::from_pt(0.0);
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@ -243,18 +252,21 @@ impl FontHandleMethods for FontHandle {
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}
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}
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return FontMetrics {
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let metrics = FontMetrics {
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underline_size: underline_size,
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underline_offset: underline_offset,
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strikeout_size: strikeout_size,
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strikeout_offset: strikeout_offset,
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leading: geometry::from_pt(0.0), //FIXME
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leading: leading,
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x_height: x_height,
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em_size: em_size,
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ascent: ascent,
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descent: -descent, // linux font's seem to use the opposite sign from mac
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max_advance: max_advance
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}
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};
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debug!("Font metrics (@{:f} pt): {:?}", geometry::to_pt(em_size), metrics);
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return metrics;
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}
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fn get_table_for_tag(&self, _: FontTableTag) -> Option<FontTable> {
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@ -9,6 +9,9 @@ use geom::size::Size2D;
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use std::num::{NumCast, One, Zero};
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use std::fmt;
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// An Au is an "App Unit" and represents 1/60th of a CSS pixel. It was
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// originally proposed in 2002 as a standard unit of measure in Gecko.
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// See https://bugzilla.mozilla.org/show_bug.cgi?id=177805 for more info.
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pub struct Au(i32);
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// We don't use #[deriving] here for inlining.
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@ -225,3 +228,8 @@ pub fn from_pt(pt: f64) -> Au {
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from_px((pt / 72f64 * 96f64) as int)
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}
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// assumes 72 points per inch, and 96 px per inch
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pub fn to_pt(au: Au) -> f64 {
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(*au as f64) / 60f64 * 72f64 / 96f64
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}
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