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[hb-style] Fix the sign of slant ratios 

We want negative slant angles to yield
positive slant ratios. Fix that.

Test included.
This commit is contained in:
Matthias Clasen 2022-02-18 18:05:58 -06:00 committed by Behdad Esfahbod
parent e76061a737
commit 16b232be0e
3 changed files with 17 additions and 3 deletions
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4
src/hb-style.cc
View File

@ -46,13 +46,13 @@
static inline float static inline float
_hb_angle_to_ratio (float a) _hb_angle_to_ratio (float a)
{ {
return tanf (a * float (M_PI / 180.)); return - tanf (a * float (M_PI / 180.));
} }
static inline float static inline float
_hb_ratio_to_angle (float r) _hb_ratio_to_angle (float r)
{ {
return atanf (r) * float (180. / M_PI); return - atanf (r) * float (180. / M_PI);
} }
/** /**

4
src/hb-style.h
View File

@ -43,8 +43,10 @@ HB_BEGIN_DECLS
* @HB_STYLE_TAG_SLANT_ANGLE: Used to vary between upright and slanted text. Values * @HB_STYLE_TAG_SLANT_ANGLE: Used to vary between upright and slanted text. Values
* must be greater than -90 and less than +90. Values can be interpreted as * must be greater than -90 and less than +90. Values can be interpreted as
* the angle, in counter-clockwise degrees, of oblique slant from whatever the * the angle, in counter-clockwise degrees, of oblique slant from whatever the
* designer considers to be upright for that font design. * designer considers to be upright for that font design. Typical right-leaning
* Italic fonts have a negative slant angle (typically around -12)
* @HB_STYLE_TAG_SLANT_RATIO: same as @HB_STYLE_TAG_SLANT_ANGLE expression as ratio. * @HB_STYLE_TAG_SLANT_RATIO: same as @HB_STYLE_TAG_SLANT_ANGLE expression as ratio.
* Typical right-leaning Italic fonts have a positive slant ratio (typically around 0.2)
* @HB_STYLE_TAG_WIDTH: Used to vary width of text from narrower to wider. * @HB_STYLE_TAG_WIDTH: Used to vary width of text from narrower to wider.
* Non-zero. Values can be interpreted as a percentage of whatever the font * Non-zero. Values can be interpreted as a percentage of whatever the font
* designer considers “normal width” for that font design. * designer considers “normal width” for that font design.

12
test/api/test-style.c
View File

@ -161,6 +161,18 @@ test_synthetic_slant (void)
hb_font_destroy (font); hb_font_destroy (font);
hb_face_destroy (face); hb_face_destroy (face);
face = hb_test_open_font_file ("fonts/notosansitalic.ttf");
font = hb_font_create (face);
/* We expect a negative angle for a typical italic font,
* which should give us a positive ratio
*/
assert_cmpfloat (hb_style_get_value (font, HB_STYLE_TAG_SLANT_ANGLE), -12);
assert_cmpfloat (hb_style_get_value (font, HB_STYLE_TAG_SLANT_RATIO), 0.21);
hb_font_destroy (font);
hb_face_destroy (face);
} }
int int