[−][src]Module kas::text::fonts
Font selection and loading
Fonts are managed by the FontLibrary, of which a static singleton
exists and can be accessed via fonts.
FontId and the default font
The FontId type is a numeric identifier for loaded fonts. It may be
default-constructed to access the default font, with number 0.
To make this work, the user of this library must load the default font before all other fonts and before any operation requiring font metrics:
if let Err(e) = kas_text::fonts::fonts().load_default() { panic!("Error loading font: {}", e); } // from now on, kas_text::fonts::FontId::default() identifies the default font
(It is not technically necessary to lead the first font with
FontLibrary::load_default; whichever font is loaded first has number 0.
If doing this, load_default must not be called at all.
It is harmless to attempt to load any font multiple times, whether with
load_default or another method.)
Font sizes
Typically, font sizes are specified in "Points". Several other units and measures come into play here. Lets start with those dating back to the early printing press:
- 1 Point = 1/72 inch (~0.35mm), by the usual DTP standard
- 1 Em is the width of a capital
M(inclusive of margin) in a font - The point size of a font refers to the number of points per em in this font
Thus, with a "12 point font", one 'M' occupies 12/72 of an inch on paper.
In digital typography, one must translate to/from pixel sizes. Here we have:
- DPI (Dots Per Inch) is the number of pixels per inch
- A scale factor is a measure of the number of pixels relative to a standard DPI, usually 96
We introduce two measures used by this library:
- DPP (Dots Per Point):
dpp = dpi / 72 = scale_factor × (96 / 72) - DPEM (Dots Per Em):
dpem = point_size × dpp
Warning: on MacOS and Apple systems, a point sometimes refers to a
(virtual) pixel, yielding dpp = 1 (or dpp = 2 on Retina screens, or
something else entirely on iPhones). On any system, DPI/DPP/scale factor
values may be set according to the user's taste rather than physical
measurements.
Finally, note that digital font files have an internally defined unit
known as the font unit. This is not normally used directly but is used
internally (including by the DPU type).
Structs
| FaceRef | Handle to a loaded font face |
| FontData | Provides access to font data |
| FontId | Font face identifier |
| FontLibrary | Library of loaded fonts |
| FontSelector | A font face selection tool |
| Stretch | The width of a font as an approximate fraction of the normal width |
| Weight | The degree of blackness or stroke thickness of a font |
Enums
| FamilyName | A possible value for the |
| Style | Allows italic or oblique faces to be selected |
Functions
| fonts | Access the |