[skrifa] new hinting options type (#1087)

Replaces the current HintingMode with a new HintingOptions type to support autohinting. Specifically, it allows for selecting the hinting engine (interpreter, auto or auto fallback). Also reintroduces a "light" mode to match FT_RENDER_MODE_LIGHT since this actually represents a different mode in the autohinter (but didn't for TrueType or CFF).

Adds the symmetric_rendering flag as well (closes #1080).

skrifa/src/outline/autohint/hint.rs

@@ -307,7 +307,7 @@ mod tests {
         super::{latin, metrics::Scale, style},
         *,
     };
-    use crate::MetadataProvider;
+    use crate::{attribute::Style, MetadataProvider};
     use raw::{
         types::{F2Dot14, GlyphId},
         FontRef, TableProvider,
@@ -413,6 +413,7 @@ mod tests {
         let scale = Scale::new(
             size,
             font.head().unwrap().units_per_em() as i32,
+            Style::Normal,
             Default::default(),
         );
         latin::hint_outline(&mut outline, &metrics, &scale);

skrifa/src/outline/autohint/instance.rs

@@ -8,7 +8,7 @@ use raw::TableProvider;
 /// Set of derived glyph styles that are used for automatic hinting.
 ///
 /// These are invariant per font so can be precomputed and reused for multiple
-/// instances when requesting automatic hinting.
+/// instances when requesting automatic hinting with [`Engine::Auto`](super::super::hint::Engine::Auto).
 #[derive(Clone, Debug)]
 pub struct GlyphStyles(Arc<GlyphStyleMap>);
 

skrifa/src/outline/autohint/latin/edges.rs

@@ -289,7 +289,7 @@ mod tests {
         },
         *,
     };
-    use crate::MetadataProvider;
+    use crate::{attribute::Style, MetadataProvider};
     use raw::{types::GlyphId, FontRef, TableProvider};
 
     #[test]
@@ -301,6 +301,7 @@ mod tests {
         let scale = metrics::Scale::new(
             16.0,
             font.head().unwrap().units_per_em() as i32,
+            Style::Normal,
             Default::default(),
         );
         let scaled_metrics = latin::metrics::scale_style_metrics(&unscaled_metrics, scale);

skrifa/src/outline/autohint/latin/hint.rs

@@ -562,7 +562,7 @@ mod tests {
         },
         *,
     };
-    use crate::MetadataProvider;
+    use crate::{attribute::Style, MetadataProvider};
     use raw::{types::GlyphId, FontRef, TableProvider};
 
     #[test]
@@ -574,6 +574,7 @@ mod tests {
         let scale = metrics::Scale::new(
             16.0,
             font.head().unwrap().units_per_em() as i32,
+            Style::Normal,
             Default::default(),
         );
         let scaled_metrics = latin::metrics::scale_style_metrics(&unscaled_metrics, scale);

skrifa/src/outline/autohint/latin/metrics.rs

@@ -209,6 +209,7 @@ fn scale_axis_metrics(
 #[cfg(test)]
 mod tests {
     use super::{super::super::style, *};
+    use crate::attribute::Style;
     use raw::{FontRef, TableProvider};
 
     #[test]
@@ -219,6 +220,7 @@ mod tests {
         let scale = Scale::new(
             16.0,
             font.head().unwrap().units_per_em() as i32,
+            Style::Normal,
             Default::default(),
         );
         let scaled_metrics = scale_style_metrics(&unscaled_metrics, scale);

skrifa/src/outline/autohint/metrics.rs

@@ -1,11 +1,11 @@
 //! Autohinting specific metrics.
 
 use super::{
-    super::{HintingMode, LcdLayout},
+    super::Target,
     axis::Dimension,
     style::{GlyphStyleMap, StyleClass},
 };
-use crate::{collections::SmallVec, FontRef};
+use crate::{attribute::Style, collections::SmallVec, FontRef};
 use alloc::vec::Vec;
 use raw::types::{F2Dot14, Fixed, GlyphId};
 #[cfg(feature = "std")]
@@ -218,40 +218,32 @@ pub(crate) struct Scale {
 }
 
 impl Scale {
-    /// Create initial scaling parameters from font size, units per em
-    /// and hinting mode.
-    pub fn new(size: f32, units_per_em: i32, mode: HintingMode) -> Self {
+    /// Create initial scaling parameters from metrics and hinting target.
+    pub fn new(size: f32, units_per_em: i32, font_style: Style, target: Target) -> Self {
         let scale =
             (Fixed::from_bits((size * 64.0) as i32) / Fixed::from_bits(units_per_em)).to_bits();
-        let is_mono = mode == HintingMode::Strong;
-        let lcd = match mode {
-            HintingMode::Smooth { lcd_subpixel, .. } => lcd_subpixel,
-            _ => None,
-        };
-        // TODO: handle light hinting mode and italic flag
-        let is_light = false;
-        let is_italic = false;
-        let is_lcd = lcd == Some(LcdLayout::Horizontal);
-        let is_lcd_v = lcd == Some(LcdLayout::Horizontal);
         let mut flags = 0;
+        let is_italic = font_style != Style::Normal;
+        let is_mono = target == Target::Mono;
+        let is_light = target.is_light() || target.preserve_linear_metrics();
         // Snap vertical stems for monochrome and horizontal LCD rendering.
-        if is_mono || is_lcd {
+        if is_mono || target.is_lcd() {
             flags |= Self::HORIZONTAL_SNAP;
         }
         // Snap horizontal stems for monochrome and vertical LCD rendering.
-        if is_mono || is_lcd_v {
+        if is_mono || target.is_vertical_lcd() {
             flags |= Self::VERTICAL_SNAP;
         }
         // Adjust stems to full pixels unless in LCD or light modes.
-        if !(is_lcd || is_light) {
+        if !(target.is_lcd() || is_light) {
             flags |= Self::STEM_ADJUST;
         }
         if is_mono {
             flags |= Self::MONO;
         }
         // Disable horizontal hinting completely for LCD, light hinting
         // and italic fonts.
-        if is_lcd || is_light || is_italic {
+        if target.is_lcd() || is_light || is_italic {
             flags |= Self::NO_HORIZONTAL;
         }
         Self {

skrifa/src/outline/glyf/hint/engine/dispatch.rs

@@ -39,9 +39,9 @@ impl<'a> Engine<'a> {
                     self.graphics.reset_retained();
                 }
                 // Set backward compatibility mode
-                if self.graphics.mode.preserve_linear_metrics() {
+                if self.graphics.target.preserve_linear_metrics() {
                     self.graphics.backward_compatibility = true;
-                } else if self.graphics.mode.is_smooth() {
+                } else if self.graphics.target.is_smooth() {
                     self.graphics.backward_compatibility =
                         (self.graphics.instruct_control & 0x4) == 0;
                 } else {

skrifa/src/outline/glyf/hint/engine/graphics.rs

@@ -568,7 +568,7 @@ impl<'a> Engine<'a> {
         }
         // If preserving linear metrics, prevent modification of the backward
         // compatibility flag.
-        if selector == 3 && self.graphics.mode.preserve_linear_metrics() {
+        if selector == 3 && self.graphics.target.preserve_linear_metrics() {
             return Ok(());
         }
         match (self.program.initial, selector) {

skrifa/src/outline/glyf/hint/engine/misc.rs

@@ -42,14 +42,15 @@ impl<'a> Engine<'a> {
             result |= FONT_VARIATIONS_RESULT_BIT;
         }
         // The following only apply for smooth hinting.
-        if self.graphics.mode.is_smooth() {
+        if self.graphics.target.is_smooth() {
             // Subpixel hinting [cleartype enabled] (selector bit: 6, result bit: 13)
             // (always enabled)
             if (selector & SUBPIXEL_HINTING_SELECTOR_BIT) != 0 {
                 result |= SUBPIXEL_HINTING_RESULT_BIT;
             }
             // Vertical LCD subpixels? (selector bit: 8, result bit: 15)
-            if (selector & VERTICAL_LCD_SELECTOR_BIT) != 0 && self.graphics.mode.is_vertical_lcd() {
+            if (selector & VERTICAL_LCD_SELECTOR_BIT) != 0 && self.graphics.target.is_vertical_lcd()
+            {
                 result |= VERTICAL_LCD_RESULT_BIT;
             }
             // Subpixel positioned? (selector bit: 10, result bit: 17)
@@ -58,16 +59,17 @@ impl<'a> Engine<'a> {
                 result |= SUBPIXEL_POSITIONED_RESULT_BIT;
             }
             // Symmetrical smoothing (selector bit: 11, result bit: 18)
-            // Note: FreeType always enables this but we deviate when our own
-            // preserve linear metrics flag is enabled.
+            // Note: FreeType always enables this but we allow direct control
+            // with our own flag.
+            // See <https://github.com/googlefonts/fontations/issues/1080>
             if (selector & SYMMETRICAL_SMOOTHING_SELECTOR_BIT) != 0
-                && !self.graphics.mode.preserve_linear_metrics()
+                && self.graphics.target.symmetric_rendering()
             {
                 result |= SYMMETRICAL_SMOOTHING_RESULT_BIT;
             }
             // ClearType hinting and grayscale rendering (selector bit: 12, result bit: 19)
             if (selector & GRAYSCALE_CLEARTYPE_SELECTOR_BIT) != 0
-                && self.graphics.mode.is_grayscale_cleartype()
+                && self.graphics.target.is_grayscale_cleartype()
             {
                 result |= GRAYSCALE_CLEARTYPE_RESULT_BIT;
             }
@@ -176,7 +178,7 @@ mod getinfo {
 #[cfg(test)]
 mod tests {
     use super::super::{
-        super::{super::super::LcdLayout, HintingMode},
+        super::super::super::{SmoothMode, Target},
         Engine, HintErrorKind, MockEngine,
     };
     use raw::types::F2Dot14;
@@ -210,7 +212,7 @@ mod tests {
         engine.axis_count = 1;
         engine.getinfo_test(FONT_VARIATIONS_SELECTOR_BIT, FONT_VARIATIONS_RESULT_BIT);
         // in strong hinting mode, the following selectors are always disabled
-        engine.graphics.mode = HintingMode::Strong;
+        engine.graphics.target = Target::Mono;
         for selector in [
             SUBPIXEL_HINTING_SELECTOR_BIT,
             VERTICAL_LCD_SELECTOR_BIT,
@@ -221,7 +223,7 @@ mod tests {
             engine.getinfo_test(selector, 0);
         }
         // set back to smooth mode
-        engine.graphics.mode = HintingMode::default();
+        engine.graphics.target = Target::default();
         for (selector, result) in [
             // default smooth mode is grayscale cleartype
             (
@@ -238,17 +240,18 @@ mod tests {
             engine.getinfo_test(selector, result);
         }
         // vertical lcd
-        engine.graphics.mode = HintingMode::Smooth {
-            lcd_subpixel: Some(LcdLayout::Vertical),
+        engine.graphics.target = Target::Smooth {
+            mode: SmoothMode::VerticalLcd,
             preserve_linear_metrics: true,
+            symmetric_rendering: false,
         };
         engine.getinfo_test(VERTICAL_LCD_SELECTOR_BIT, VERTICAL_LCD_RESULT_BIT);
-        // symmetical smoothing is disabled when preserving linear metrics
+        // symmetical smoothing is disabled
         engine.getinfo_test(SYMMETRICAL_SMOOTHING_SELECTOR_BIT, 0);
         // grayscale cleartype is disabled when lcd_subpixel is not None
         engine.getinfo_test(GRAYSCALE_CLEARTYPE_SELECTOR_BIT, 0);
         // reset to default to disable preserve linear metrics
-        engine.graphics.mode = HintingMode::default();
+        engine.graphics.target = Target::default();
         // now symmetrical smoothing is enabled
         engine.getinfo_test(
             SYMMETRICAL_SMOOTHING_SELECTOR_BIT,

skrifa/src/outline/glyf/hint/graphics.rs

@@ -3,7 +3,7 @@
 use super::{
     round::RoundState,
     zone::{Zone, ZonePointer},
-    F26Dot6, HintingMode, Point,
+    F26Dot6, Point, Target,
 };
 use core::ops::{Deref, DerefMut};
 
@@ -150,11 +150,11 @@ impl<'a> GraphicsState<'a> {
     pub fn reset_retained(&mut self) {
         let scale = self.scale;
         let ppem = self.ppem;
-        let mode = self.mode;
+        let mode = self.target;
         self.retained = RetainedGraphicsState {
             scale,
             ppem,
-            mode,
+            target: mode,
             ..Default::default()
         }
     }
@@ -251,8 +251,8 @@ pub struct RetainedGraphicsState {
     ///
     /// See <https://developer.apple.com/fonts/TrueType-Reference-Manual/RM04/Chap4.html#single_width_value>
     pub single_width: F26Dot6,
-    /// The user requested hinting mode.
-    pub mode: HintingMode,
+    /// The user requested hinting target.
+    pub target: Target,
     /// The scale factor for the current instance. Conversion from font units
     /// to 26.6 for current ppem.
     pub scale: i32,
@@ -265,11 +265,11 @@ pub struct RetainedGraphicsState {
 }
 
 impl RetainedGraphicsState {
-    pub fn new(scale: i32, ppem: i32, mode: HintingMode) -> Self {
+    pub fn new(scale: i32, ppem: i32, target: Target) -> Self {
         Self {
             scale,
             ppem,
-            mode,
+            target,
             ..Default::default()
         }
     }
@@ -292,7 +292,7 @@ impl Default for RetainedGraphicsState {
             scan_type: 0,
             single_width_cutin: F26Dot6::ZERO,
             single_width: F26Dot6::ZERO,
-            mode: Default::default(),
+            target: Default::default(),
             scale: 0,
             ppem: 0,
             is_rotated: false,

skrifa/src/outline/glyf/hint/instance.rs

@@ -10,7 +10,7 @@ use super::{
     program::{Program, ProgramState},
     value_stack::ValueStack,
     zone::Zone,
-    HintOutline, HintingMode, PointFlags,
+    HintOutline, PointFlags, Target,
 };
 use alloc::vec::Vec;
 use raw::{
@@ -38,7 +38,7 @@ impl HintInstance {
         outlines: &Outlines,
         scale: i32,
         ppem: i32,
-        mode: HintingMode,
+        target: Target,
         coords: &[F2Dot14],
     ) -> Result<(), HintError> {
         self.setup(outlines, scale, coords);
@@ -53,7 +53,7 @@ impl HintInstance {
         let glyph = Zone::default();
         let mut stack_buf = vec![0; self.max_stack];
         let value_stack = ValueStack::new(&mut stack_buf, false);
-        let graphics = RetainedGraphicsState::new(scale, ppem, mode);
+        let graphics = RetainedGraphicsState::new(scale, ppem, target);
         let mut engine = Engine::new(
             outlines,
             ProgramState::new(outlines.fpgm, outlines.prep, &[], Program::Font),
@@ -92,9 +92,9 @@ impl HintInstance {
     /// by the hinter settings or the `prep` table.
     pub fn backward_compatibility(&self) -> bool {
         // Set backward compatibility mode
-        if self.graphics.mode.preserve_linear_metrics() {
+        if self.graphics.target.preserve_linear_metrics() {
             true
-        } else if self.graphics.mode.is_smooth() {
+        } else if self.graphics.target.is_smooth() {
             (self.graphics.instruct_control & 0x4) == 0
         } else {
             false

skrifa/src/outline/glyf/hint/mod.rs

@@ -16,7 +16,7 @@ mod storage;
 mod value_stack;
 mod zone;
 
-use super::super::{HintingMode, LcdLayout};
+use super::super::Target;
 
 use read_fonts::{
     tables::glyf::PointFlags,
@@ -45,42 +45,3 @@ pub struct HintOutline<'a> {
     pub is_composite: bool,
     pub coords: &'a [F2Dot14],
 }
-
-// Helpers for deriving various flags from the mode which
-// change the behavior of certain instructions.
-// See <https://gitlab.freedesktop.org/freetype/freetype/-/blob/57617782464411201ce7bbc93b086c1b4d7d84a5/src/truetype/ttgload.c#L2222>
-impl HintingMode {
-    fn is_smooth(&self) -> bool {
-        matches!(self, Self::Smooth { .. })
-    }
-
-    fn is_grayscale_cleartype(&self) -> bool {
-        matches!(
-            self,
-            Self::Smooth {
-                lcd_subpixel: None,
-                ..
-            }
-        )
-    }
-
-    fn is_vertical_lcd(&self) -> bool {
-        matches!(
-            self,
-            Self::Smooth {
-                lcd_subpixel: Some(LcdLayout::Vertical),
-                ..
-            }
-        )
-    }
-
-    fn preserve_linear_metrics(&self) -> bool {
-        matches!(
-            self,
-            Self::Smooth {
-                preserve_linear_metrics: true,
-                ..
-            }
-        )
-    }
-}