DirectWrite font backend for Windows

components/gfx/platform/windows/font.rs

@@ -0,0 +1,204 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// NOTE: https://www.chromium.org/directwrite-font-proxy has useful
+// information for an approach that we'll likely need to take when the
+// renderer moves to a sandboxed process.
+
+use app_units::Au;
+use font::{FontHandleMethods, FontMetrics, FontTableMethods};
+use font::{FontTableTag, FractionalPixel};
+use platform::font_template::{FontTemplateData};
+use platform::windows::font_list::{font_from_atom};
+use platform::windows::font_context::{FontContextHandle};
+use std::sync::Arc;
+use style::computed_values::{font_stretch, font_weight};
+use text::glyph::GlyphId;
+use dwrote::{Font, FontFace};
+use dwrote::{FontWeight, FontStretch, FontStyle};
+
+// 1em = 12pt = 16px, assuming 72 points per inch and 96 px per inch
+fn pt_to_px(pt: f64) -> f64 { pt / 72. * 96. }
+fn em_to_px(em: f64) -> f64 { em * 16. }
+fn au_from_em(em: f64) -> Au { Au::from_f64_px(em_to_px(em)) }
+fn au_from_pt(pt: f64) -> Au { Au::from_f64_px(pt_to_px(pt)) }
+
+pub struct FontTable {
+    data: Vec<u8>,
+}
+
+impl FontTable {
+    pub fn wrap(data: &[u8]) -> FontTable {
+        FontTable { data: data.to_vec() }
+    }
+}
+
+impl FontTableMethods for FontTable {
+    fn buffer(&self) -> &[u8] {
+        &self.data
+    }
+}
+
+#[derive(Debug)]
+pub struct FontHandle {
+    font_data: Arc<FontTemplateData>,
+    font: Font,
+    face: FontFace,
+    em_size: f32,
+    du_per_em: f32,
+    du_to_px: f32,
+    scaled_du_to_px: f32,
+}
+
+impl FontHandle {
+}
+
+impl FontHandleMethods for FontHandle {
+    fn new_from_template(_: &FontContextHandle, template: Arc<FontTemplateData>, pt_size: Option<Au>)
+                         -> Result<Self, ()>
+    {
+        if let Some(_) = template.bytes {
+            // FIXME we should load from template.bytes
+            Err(())
+        } else {
+            let font = font_from_atom(&template.identifier);
+            let face = font.create_font_face();
+
+            let pt_size = pt_size.unwrap_or(au_from_pt(12.));
+            let du_per_em = face.metrics().designUnitsPerEm as f32;
+
+            let em_size = pt_size.to_f32_px() / 16.;
+            let design_units_per_pixel = du_per_em / 16.;
+
+            let design_units_to_pixels = 1. / design_units_per_pixel;
+            let scaled_design_units_to_pixels = em_size / design_units_per_pixel;
+
+            Ok(FontHandle {
+                font_data: template.clone(),
+                font: font,
+                face: face,
+                em_size: em_size,
+                du_per_em: du_per_em,
+                du_to_px: design_units_to_pixels,
+                scaled_du_to_px: scaled_design_units_to_pixels,
+            })
+        }
+    }
+
+    fn template(&self) -> Arc<FontTemplateData> {
+        self.font_data.clone()
+    }
+
+    fn family_name(&self) -> String {
+        self.font.family_name()
+    }
+
+    fn face_name(&self) -> String {
+        self.font.face_name()
+    }
+
+    fn is_italic(&self) -> bool {
+        match self.font.style() {
+            FontStyle::Normal => false,
+            FontStyle::Oblique | FontStyle::Italic => true,
+        }
+    }
+
+    fn boldness(&self) -> font_weight::T {
+        match self.font.weight() {
+            FontWeight::Thin => font_weight::T::Weight100,
+            FontWeight::ExtraLight => font_weight::T::Weight200,
+            FontWeight::Light => font_weight::T::Weight300,
+            // slightly lighter gray
+            FontWeight::SemiLight => font_weight::T::Weight300,
+            FontWeight::Regular => font_weight::T::Weight400,
+            FontWeight::Medium => font_weight::T::Weight500,
+            FontWeight::SemiBold => font_weight::T::Weight600,
+            FontWeight::Bold => font_weight::T::Weight700,
+            FontWeight::ExtraBold => font_weight::T::Weight800,
+            FontWeight::Black => font_weight::T::Weight900,
+            // slightly blacker black
+            FontWeight::ExtraBlack => font_weight::T::Weight900,
+        }
+    }
+
+    fn stretchiness(&self) -> font_stretch::T {
+        match self.font.stretch() {
+            FontStretch::Undefined => font_stretch::T::normal,
+            FontStretch::UltraCondensed => font_stretch::T::ultra_condensed,
+            FontStretch::ExtraCondensed => font_stretch::T::extra_condensed,
+            FontStretch::Condensed => font_stretch::T::condensed,
+            FontStretch::SemiCondensed => font_stretch::T::semi_condensed,
+            FontStretch::Normal => font_stretch::T::normal,
+            FontStretch::SemiExpanded => font_stretch::T::semi_expanded,
+            FontStretch::Expanded => font_stretch::T::expanded,
+            FontStretch::ExtraExpanded => font_stretch::T::extra_expanded,
+            FontStretch::UltraExpanded => font_stretch::T::ultra_expanded,
+        }
+    }
+
+    fn glyph_index(&self, codepoint: char) -> Option<GlyphId> {
+        let glyph = self.face.get_glyph_indices(&[codepoint as u32])[0];
+        if glyph == 0 {
+            return None;
+        }
+        Some(glyph as GlyphId)
+    }
+
+    fn glyph_h_advance(&self, glyph: GlyphId) -> Option<FractionalPixel> {
+        if glyph == 0 {
+            return None;
+        }
+
+        let gm = self.face.get_design_glyph_metrics(&[glyph as u16], false)[0];
+        let f = (gm.advanceWidth as f32 * self.scaled_du_to_px) as FractionalPixel;
+
+        Some(f)
+    }
+
+    /// Can this font do basic horizontal LTR shaping without Harfbuzz?
+    fn can_do_fast_shaping(&self) -> bool {
+        // TODO copy CachedKernTable from the MacOS X implementation to
+        // somehwere global and use it here.  We could also implement the
+        // IDirectWriteFontFace1 interface and use the glyph kerning pair
+        // methods there.
+        false
+    }
+
+    fn glyph_h_kerning(&self, _: GlyphId, _: GlyphId) -> FractionalPixel {
+        0.0
+    }
+
+    fn metrics(&self) -> FontMetrics {
+        let dm = self.face.metrics();
+
+        let au_from_du = |du| -> Au { Au::from_f32_px(du as f32 * self.du_to_px) };
+        let au_from_du_s = |du| -> Au { Au:: from_f32_px(du as f32 * self.scaled_du_to_px) };
+
+        // anything that we calculate and don't just pull out of self.face.metrics
+        // is pulled out here for clarity
+        let leading = dm.ascent - dm.capHeight;
+        
+        let metrics = FontMetrics {
+            underline_size:   au_from_du(dm.underlineThickness as i32),
+            underline_offset: au_from_du_s(dm.underlinePosition as i32),
+            strikeout_size:   au_from_du(dm.strikethroughThickness as i32),
+            strikeout_offset: au_from_du_s(dm.strikethroughPosition as i32),
+            leading:          au_from_du_s(leading as i32),
+            x_height:         au_from_du_s(dm.xHeight as i32),
+            em_size:          au_from_em(self.em_size as f64),
+            ascent:           au_from_du_s(dm.ascent as i32),
+            descent:          au_from_du_s(dm.descent as i32),
+            max_advance:      au_from_pt(0.0), // FIXME
+            average_advance:  au_from_pt(0.0), // FIXME
+            line_gap:         au_from_du(dm.lineGap as i32),
+        };
+        debug!("Font metrics (@{} pt): {:?}", self.em_size * 12., metrics);
+        metrics
+    }
+
+    fn table_for_tag(&self, tag: FontTableTag) -> Option<FontTable> {
+        self.face.get_font_table(tag).map(|bytes| FontTable { data: bytes })
+    }
+}