[cairo] Document scale-factor business

This commit is contained in:
Behdad Esfahbod 2022-12-26 15:52:55 -07:00
parent 4e3e879c1c
commit 0fe0cdf066
1 changed files with 32 additions and 0 deletions

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@ -609,6 +609,35 @@ hb_cairo_scaled_font_get_font (cairo_scaled_font_t *scaled_font)
* Sets the scale factor of the @font_face. Default scale * Sets the scale factor of the @font_face. Default scale
* factor is zero. * factor is zero.
* *
* When a #cairo_font_face_t is created from a #hb_face_t using
* hb_cairo_font_face_create_for_face(), such face will create
* #hb_font_t objects during scaled-font creation. The scale
* factor defines how the scale set on such #hb_font_t objects
* relates to the font-matrix (as such font size) of the cairo
* scaled-font.
*
* If the scale-factor is zero (default), then the scale of the
* #hb_font_t object will be left at default, which is the UPEM
* value of the respective #hb_face_t.
*
* If the scale-factor is set to non-zero, then the X and Y scale
* of the #hb_font_t object will be respectively set to the
* @scale_factor times the xx and yy elements of the scale-matrix
* of the cairo scaled-font being created.
*
* When using the hb_cairo_glyphs_from_buffer() API to convert
* HarfBuzz glyph buffer resulted from shaping with such a hb_font_t,
* if the scale-factor was non-zero, you can pass it directly to
* that API. If the scale-factor was zero however, you need to
* calculate the correct scale-factor to pass to that API by
* dividing the #hb_font_t scale-factor by the cairo scaled-font's
* scale-matrix scale-factor. This assumes a uniform scale.
*
* If the cairo-face was created using the alternative constructor
* hb_cairo_font_face_create_for_font(), you are on your own
* computing the correct scale-factor to pass to
* hb_cairo_glyphs_from_buffer().
*
* Since: REPLACEME * Since: REPLACEME
*/ */
void void
@ -657,6 +686,9 @@ hb_cairo_font_face_get_scale_factor (cairo_font_face_t *font_face)
* Extracts information from @buffer in a form that can be * Extracts information from @buffer in a form that can be
* passed to cairo_show_text_glyphs(). * passed to cairo_show_text_glyphs().
* *
* See hb_cairo_font_face_set_scale_factor() for the details of
* the @scale_factor argument.
*
* Since: REPLACEME * Since: REPLACEME
*/ */
void void