Auto merge of #26697 - utsavoza:ugo/issue-11681/22-05-2020, r=jdm

Implement CanvasRenderingContext2d.fillText

The PR consists of broadly two main changes:
- Implementation of Canvas2dRenderingContext.font
- Basic implementation of Canvas2dRenderingContext.fillText

Although I am not fully sure about the long term goals for the canvas backend in Servo, I assumed limited scope for font and text handling (should support simple text drawing with font selection) in the current implementation as I believe a more complete implementation would eventually be brought in as a part of #22957.

---
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #11681
- [x] There are tests for these changes

components/style/Cargo.toml

@@ -39,6 +39,7 @@ derive_more = "0.99"
 encoding_rs = { version = "0.8", optional = true }
 euclid = "0.20"
 fallible = { path = "../fallible" }
+font-kit = "0.7"
 fxhash = "0.2"
 hashglobe = { path = "../hashglobe" }
 html5ever = { version = "0.25", optional = true }

components/style/lib.rs

@@ -40,6 +40,8 @@ extern crate debug_unreachable;
 extern crate derive_more;
 extern crate euclid;
 extern crate fallible;
+#[cfg(feature = "servo")]
+extern crate font_kit;
 extern crate fxhash;
 #[cfg(feature = "gecko")]
 #[macro_use]

components/style/properties/properties.mako.rs

@@ -2602,6 +2602,7 @@ pub mod style_structs {
     % for style_struct in data.active_style_structs():
         % if style_struct.name == "Font":
         #[derive(Clone, Debug, MallocSizeOf)]
+        #[cfg_attr(feature = "servo", derive(Serialize, Deserialize))]
         % else:
         #[derive(Clone, Debug, MallocSizeOf, PartialEq)]
         % endif

components/style/values/computed/font.rs

@@ -22,6 +22,12 @@ use crate::values::specified::length::{FontBaseSize, NoCalcLength};
 use crate::values::CSSFloat;
 use crate::Atom;
 use cssparser::{serialize_identifier, CssStringWriter, Parser};
+#[cfg(feature = "servo")]
+use font_kit::family_name::FamilyName as FontKitFamilyName;
+#[cfg(feature = "servo")]
+use font_kit::properties::{
+    Stretch as FontKitFontStretch, Style as FontKitFontStyle, Weight as FontKitFontWeight,
+};
 #[cfg(feature = "gecko")]
 use malloc_size_of::{MallocSizeOf, MallocSizeOfOps};
 use std::fmt::{self, Write};
@@ -69,6 +75,13 @@ impl ToAnimatedValue for FontWeight {
     }
 }
 
+#[cfg(feature = "servo")]
+impl From<FontWeight> for FontKitFontWeight {
+    fn from(font_weight: FontWeight) -> Self {
+        FontKitFontWeight(font_weight.0)
+    }
+}
+
 #[derive(
     Animate,
     Clone,
@@ -81,6 +94,7 @@ impl ToAnimatedValue for FontWeight {
     ToCss,
     ToResolvedValue,
 )]
+#[cfg_attr(feature = "servo", derive(Serialize, Deserialize))]
 /// The computed value of font-size
 pub struct FontSize {
     /// The size.
@@ -179,7 +193,7 @@ impl ToAnimatedValue for FontSize {
 }
 
 #[derive(Clone, Debug, Eq, PartialEq, ToComputedValue, ToResolvedValue)]
-#[cfg_attr(feature = "servo", derive(Hash, MallocSizeOf))]
+#[cfg_attr(feature = "servo", derive(Hash, MallocSizeOf, Serialize, Deserialize))]
 /// Specifies a prioritized list of font family names or generic family names.
 pub struct FontFamily {
     /// The actual list of family names.
@@ -444,9 +458,29 @@ impl SingleFontFamily {
 }
 
 #[cfg(feature = "servo")]
+impl From<&SingleFontFamily> for FontKitFamilyName {
+    fn from(font_family: &SingleFontFamily) -> Self {
+        match font_family {
+            SingleFontFamily::FamilyName(family_name) => {
+                FontKitFamilyName::Title(family_name.to_css_string())
+            },
+            SingleFontFamily::Generic(GenericFontFamily::Serif) => FontKitFamilyName::Serif,
+            SingleFontFamily::Generic(GenericFontFamily::SansSerif) => FontKitFamilyName::SansSerif,
+            SingleFontFamily::Generic(GenericFontFamily::Monospace) => FontKitFamilyName::Monospace,
+            SingleFontFamily::Generic(GenericFontFamily::Fantasy) => FontKitFamilyName::Fantasy,
+            SingleFontFamily::Generic(GenericFontFamily::Cursive) => FontKitFamilyName::Cursive,
+            SingleFontFamily::Generic(family_name) => {
+                warn!("unsupported font family name: {:?}", family_name);
+                FontKitFamilyName::SansSerif
+            },
+        }
+    }
+}
+
 #[derive(
     Clone, Debug, Eq, Hash, MallocSizeOf, PartialEq, ToComputedValue, ToResolvedValue, ToShmem,
 )]
+#[cfg_attr(feature = "servo", derive(Serialize, Deserialize))]
 /// A list of SingleFontFamily
 pub struct FontFamilyList(Box<[SingleFontFamily]>);
 
@@ -931,6 +965,17 @@ impl ToCss for FontStyle {
     }
 }
 
+#[cfg(feature = "servo")]
+impl From<FontStyle> for FontKitFontStyle {
+    fn from(font_style: FontStyle) -> Self {
+        match font_style {
+            FontStyle::Normal => FontKitFontStyle::Normal,
+            FontStyle::Italic => FontKitFontStyle::Italic,
+            FontStyle::Oblique(_) => FontKitFontStyle::Oblique,
+        }
+    }
+}
+
 /// A value for the font-stretch property per:
 ///
 /// https://drafts.csswg.org/css-fonts-4/#propdef-font-stretch
@@ -953,6 +998,13 @@ impl FontStretch {
     }
 }
 
+#[cfg(feature = "servo")]
+impl From<FontStretch> for FontKitFontStretch {
+    fn from(stretch: FontStretch) -> Self {
+        FontKitFontStretch(stretch.value())
+    }
+}
+
 impl ToAnimatedValue for FontStretch {
     type AnimatedValue = Percentage;
 

components/style/values/specified/font.rs

@@ -497,6 +497,7 @@ impl ToComputedValue for FontStretch {
     ToResolvedValue,
     ToShmem,
 )]
+#[cfg_attr(feature = "servo", derive(Serialize, Deserialize))]
 #[allow(missing_docs)]
 pub enum KeywordSize {
     #[css(keyword = "xx-small")]
@@ -541,6 +542,7 @@ impl Default for KeywordSize {
     ToResolvedValue,
     ToShmem,
 )]
+#[cfg_attr(feature = "servo", derive(Serialize, Deserialize))]
 /// Additional information for keyword-derived font sizes.
 pub struct KeywordInfo {
     /// The keyword used