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crates/strato-ui-renderer/src/fonts/font_kit.rs

StratoSDK / crates / strato-ui-renderer / src / fonts / font_kit.rs

1	//! A text rasterizer backed by [`font_kit`] that supports rasterizing at subpixel offsets
2
3	use std::sync::Arc;
4
5	use anyhow::Result;
6	use dashmap::DashMap;
7	use font_kit::canvas::{Canvas, RasterizationOptions};
8	use font_kit::font::Font;
9	use font_kit::hinting::HintingOptions;
10	use pathfinder_geometry::rect::RectI;
11	use pathfinder_geometry::transform2d::Transform2F;
12	use pathfinder_geometry::vector::{vec2i, Vector2F, Vector2I};
13	use strato_ui_core::fonts::canvas::RasterFormat;
14	use strato_ui_core::fonts::{
15	FontId, GlyphId, Properties, RasterizedGlyph, Style, SubpixelAlignment, Weight,
16	};
17	use strato_ui_core::rendering;
18
19	#[cfg(target_os = "macos")]
20	use crate::platform::mac::AutoreleasePoolGuard;
21
22	/// A simpler rasterizer backed by font-kit.
23	pub(crate) struct Rasterizer {
24	fonts: DashMap<FontId, Arc<Font>>,
25	}
26
27	impl Rasterizer {
28	pub fn new() -> Self {
29	Self {
30	fonts: Default::default(),
31	}
32	}
33
34	pub fn insert(&self, font_id: FontId, font: Arc<Font>) {
35	self.fonts.insert(font_id, font);
36	}
37
38	pub fn font_for_id(&self, font_id: FontId) -> Arc<Font> {
39	self.fonts.get(&font_id).expect("Font must exist").clone()
40	}
41
42	pub fn glyph_raster_bounds(
43	&self,
44	font_id: FontId,
45	point_size: f32,
46	glyph_id: GlyphId,
47	scale: Vector2F,
48	_glyph_config: &rendering::GlyphConfig,
49	) -> Result<RectI> {
50	let raw_raster_bounds = self.font_for_id(font_id).raster_bounds(
51	glyph_id,
52	point_size,
53	Transform2F::from_scale(scale),
54	HintingOptions::None,
55	RasterizationOptions::GrayscaleAa,
56	)?;
57	if raw_raster_bounds.size() == Vector2I::zero() {
58	// Don't adjust the size of a glyph with a default size of zero.
59	return Ok(raw_raster_bounds);
60	}
61	// The default raster bounds provided by font-kit sometimes clip pixels
62	// off of anti-aliased glyphs; add one pixel to the glyph bounds to
63	// compensate. We only adjust the origin vertically because the extra
64	// pixel of height changes the baseline; the extra pixel on the right
65	// side doesn't change positioning (as the origin is on the left edge of
66	// the glyph).
67	let fudge_factor = vec2i(1, 1);
68	let offset = vec2i(0, 1);
69	Ok(RectI::new(
70	raw_raster_bounds.origin() - offset,
71	raw_raster_bounds.size() + fudge_factor,
72	))
73	}
74
75	#[allow(clippy::too_many_arguments)]
76	pub fn rasterize_glyph(
77	&self,
78	font_id: FontId,
79	point_size: f32,
80	glyph_id: GlyphId,
81	scale: Vector2F,
82	subpixel_alignment: SubpixelAlignment,
83	glyph_config: &rendering::GlyphConfig,
84	format: RasterFormat,
85	) -> Result<RasterizedGlyph> {
86	// On macOS, this function calls into Core Graphics and Core Text
87	// (`CGBitmapContextCreate` per glyph plus `raster_bounds` reading font
88	// metadata), each of which leaves transient bookkeeping objects in the
89	// thread's autorelease pool. Because this is invoked during Metal
90	// frame rendering on the main thread, hundreds of those objects can
91	// accumulate between run-loop turns before AppKit's outer pool
92	// drains. A local pool bounds that peak without relying on the outer
93	// pool. The guard drains on `Drop`, covering the error paths from `?`
94	// below and any panics from `font_kit`.
95	#[cfg(target_os = "macos")]
96	let _pool = AutoreleasePoolGuard::new();
97
98	let bounds =
99	self.glyph_raster_bounds(font_id, point_size, glyph_id, scale, glyph_config)?;
100	let mut canvas = Canvas::new(bounds.size(), raster_format_to_font_kit(format));
101
102	let base_transform = Transform2F::from_scale(scale).translate(-bounds.origin().to_f32());
103	let aligned_transform = base_transform.translate(subpixel_alignment.to_offset());
104
105	self.font_for_id(font_id).rasterize_glyph(
106	&mut canvas,
107	glyph_id,
108	point_size,
109	aligned_transform,
110	HintingOptions::None,
111	RasterizationOptions::GrayscaleAa,
112	)?;
113
114	Ok(RasterizedGlyph {
115	canvas: canvas.into(),
116	// Crates.io font-kit does not expose Warp's color-font helper. Keep
117	// emoji/color-glyph handling disabled until Strato owns that path.
118	is_emoji: false,
119	})
120	}
121	}
122
123	pub fn properties_to_font_kit(properties: Properties) -> font_kit::properties::Properties {
124	font_kit::properties::Properties {
125	style: style_to_font_kit(properties.style),
126	weight: weight_to_font_kit(properties.weight),
127	stretch: Default::default(),
128	}
129	}
130
131	fn raster_format_to_font_kit(format: RasterFormat) -> font_kit::canvas::Format {
132	use font_kit::canvas::Format as FKFormat;
133	match format {
134	RasterFormat::Rgba32 => FKFormat::Rgba32,
135	RasterFormat::Rgb24 => FKFormat::Rgb24,
136	RasterFormat::A8 => FKFormat::Rgb24,
137	}
138	}
139
140	fn weight_to_font_kit(weight: Weight) -> font_kit::properties::Weight {
141	match weight {
142	Weight::Thin => font_kit::properties::Weight::THIN,
143	Weight::ExtraLight => font_kit::properties::Weight::EXTRA_LIGHT,
144	Weight::Light => font_kit::properties::Weight::LIGHT,
145	Weight::Normal => font_kit::properties::Weight::NORMAL,
146	Weight::Medium => font_kit::properties::Weight::MEDIUM,
147	Weight::Semibold => font_kit::properties::Weight::SEMIBOLD,
148	Weight::Bold => font_kit::properties::Weight::BOLD,
149	Weight::ExtraBold => font_kit::properties::Weight::EXTRA_BOLD,
150	Weight::Black => font_kit::properties::Weight::BLACK,
151	}
152	}
153
154	fn style_to_font_kit(value: Style) -> font_kit::properties::Style {
155	match value {
156	Style::Normal => font_kit::properties::Style::Normal,
157	Style::Italic => font_kit::properties::Style::Italic,
158	}
159	}
160

Seregon/StratoSDK