ref: 69da54cacc0056a40fc7f88278c4c60fd35e7bb9
parent: ba86636b14f876fa369c84467409b3b812d47e94
author: Werner Lemberg <[email protected]>
date: Wed Apr 26 05:58:28 EDT 2017
Document that some FT_Size_Metrics values are always rounded.
--- a/include/freetype/freetype.h
+++ b/include/freetype/freetype.h
@@ -1506,27 +1506,34 @@
/* fractional pixels. Only relevant for scalable */
/* font formats. */
/* */
- /* ascender :: The ascender in 26.6 fractional pixels. See */
- /* @FT_FaceRec for the details. */
+ /* ascender :: The ascender in 26.6 fractional pixels, rounded up */
+ /* to an integer value. See @FT_FaceRec for the */
+ /* details. */
/* */
- /* descender :: The descender in 26.6 fractional pixels. See */
- /* @FT_FaceRec for the details. */
+ /* descender :: The descender in 26.6 fractional pixels, rounded */
+ /* down to an integer value. See @FT_FaceRec for the */
+ /* details. */
/* */
- /* height :: The height in 26.6 fractional pixels. See */
- /* @FT_FaceRec for the details. */
+ /* height :: The height in 26.6 fractional pixels, rounded to */
+ /* an integer value. See @FT_FaceRec for the */
+ /* details. */
/* */
/* max_advance :: The maximum advance width in 26.6 fractional */
- /* pixels. See @FT_FaceRec for the details. */
+ /* pixels, rounded to an integer value. See */
+ /* @FT_FaceRec for the details. */
/* */
/* <Note> */
/* The scaling values, if relevant, are determined first during a */
/* size changing operation. The remaining fields are then set by the */
/* driver. For scalable formats, they are usually set to scaled */
- /* values of the corresponding fields in @FT_FaceRec. */
+ /* values of the corresponding fields in @FT_FaceRec. Some values */
+ /* like ascender or descender are rounded for historical reasons; */
+ /* more precise values (for outline fonts) can be derived by scaling */
+ /* the corresponding @FT_FaceRec values manually. */
/* */
- /* Note that due to glyph hinting, these values might not be exact */
- /* for certain fonts. Thus they must be treated as unreliable */
- /* with an error margin of at least one pixel! */
+ /* Note that due to glyph hinting and the selected rendering mode */
+ /* these values are usually not exact; consequently, they must be */
+ /* treated as unreliable with an error margin of at least one pixel! */
/* */
/* Indeed, the only way to get the exact metrics is to render _all_ */
/* glyphs. As this would be a definite performance hit, it is up to */