Next stage of refactoring font system. This commit introduces

the font cache task, and adapts client code to use it. It also
cleans up some existing code paths.

- Fonts are only read once from disk while in use (they
  are discarded if the reference count reaches zero, however).
  This saves memory and prevents unnecessary reading from disk.
- It will be easier to add web font support, as all fonts
  are created and managed in a single place and the entire
  pipeline ensures that only one in-memory copy of font data
  is required.

An overview of how the pieces fit together:

FontTemplate - A structure containing everything that
is required to create (and select) font handles. This
structure is shared among all matching font handles
(via Arc).

FontTemplateData - A platform specific structure that
contains the actual font data inside a template (this is
a byte array on Linux/Android, CTFont on Mac).

FontHandle - An opaque, platform specific handle to
a font instance. Each FontHandle contains an Arc<>
reference to the FontTemplate it was created from.

FontCache - This is a separate task, that is responsible
for loading and caching FontTemplate structures. There
is one FontCache per constellation. It is only ever accessed
via the FontContext described below.

FontContext - This is the public interface to the FontCache
and is used by the layout and render code to create font
handles. These must *not* be shared between threads. There
is typically one FontContext per thread/task.

1 files changed, 213 insertions, 0 deletions

diff --git a/src/components/gfx/font_cache_task.rs b/src/components/gfx/font_cache_task.rs
new file mode 100644
index 00000000000..55e2dad003e
--- /dev/null
+++ b/src/components/gfx/font_cache_task.rs
@@ -0,0 +1,213 @@
+/* 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/. */
+
+use platform::font_list::get_available_families;
+use platform::font_list::get_variations_for_family;
+use platform::font_list::get_last_resort_font_families;
+use platform::font_context::FontContextHandle;
+
+use std::collections::HashMap;
+use sync::Arc;
+use font_template::{FontTemplate, FontTemplateDescriptor};
+use platform::font_template::FontTemplateData;
+
+/// A list of font templates that make up a given font family.
+struct FontFamily {
+    templates: Vec<FontTemplate>,
+}
+
+impl FontFamily {
+    fn new() -> FontFamily {
+        FontFamily {
+            templates: vec!(),
+        }
+    }
+
+    /// Find a font in this family that matches a given desriptor.
+    fn find_font_for_style<'a>(&'a mut self, desc: &FontTemplateDescriptor, fctx: &FontContextHandle)
+                               -> Option<Arc<FontTemplateData>> {
+        // TODO(Issue #189): optimize lookup for
+        // regular/bold/italic/bolditalic with fixed offsets and a
+        // static decision table for fallback between these values.
+
+        // TODO(Issue #190): if not in the fast path above, do
+        // expensive matching of weights, etc.
+        for template in self.templates.mut_iter() {
+            let maybe_template = template.get_if_matches(fctx, desc);
+            if maybe_template.is_some() {
+                return maybe_template;
+            }
+        }
+
+        None
+    }
+}
+
+/// Commands that the FontContext sends to the font cache task.
+pub enum Command {
+    GetFontTemplate(String, FontTemplateDescriptor, Sender<Reply>),
+    Exit(Sender<()>),
+}
+
+/// Reply messages sent from the font cache task to the FontContext caller.
+pub enum Reply {
+    GetFontTemplateReply(Arc<FontTemplateData>),
+}
+
+/// The font cache task itself. It maintains a list of reference counted
+/// font templates that are currently in use.
+struct FontCache {
+    port: Receiver<Command>,
+    generic_fonts: HashMap<String, String>,
+    local_families: HashMap<String, FontFamily>,
+    font_context: FontContextHandle,
+}
+
+impl FontCache {
+    fn run(&mut self) {
+        loop {
+            let msg = self.port.recv();
+
+            match msg {
+                GetFontTemplate(family, descriptor, result) => {
+                    let maybe_font_template = self.get_font_template(&family, &descriptor);
+
+                    let font_template = match maybe_font_template {
+                        Some(font_template) => font_template,
+                        None => self.get_last_resort_template(&descriptor),
+                    };
+
+                    result.send(GetFontTemplateReply(font_template));
+                }
+                Exit(result) => {
+                    result.send(());
+                    break;
+                }
+            }
+        }
+    }
+
+    fn refresh_local_families(&mut self) {
+        self.local_families.clear();
+        get_available_families(|family_name| {
+            if !self.local_families.contains_key(&family_name) {
+                let family = FontFamily::new();
+                self.local_families.insert(family_name, family);
+            }
+        });
+    }
+
+    fn transform_family(&self, family: &String) -> String {
+        match self.generic_fonts.find(family) {
+            None => family.to_string(),
+            Some(mapped_family) => (*mapped_family).clone()
+        }
+    }
+
+    fn find_font_in_family<'a>(&'a mut self,
+                                   family_name: &String,
+                                   desc: &FontTemplateDescriptor) -> Option<Arc<FontTemplateData>> {
+        // TODO(Issue #188): look up localized font family names if canonical name not found
+        // look up canonical name
+        if self.local_families.contains_key(family_name) {
+            debug!("FontList: Found font family with name={:s}", family_name.to_str());
+            let s = self.local_families.get_mut(family_name);
+
+            if s.templates.len() == 0 {
+                get_variations_for_family(family_name.as_slice(), |path| {
+                    let template = FontTemplate::new(path.as_slice());
+                    s.templates.push(template);
+                });
+            }
+
+            // TODO(Issue #192: handle generic font families, like 'serif' and 'sans-serif'.
+            // if such family exists, try to match style to a font
+            let result = s.find_font_for_style(desc, &self.font_context);
+            if result.is_some() {
+                return result;
+            }
+
+            None
+        } else {
+            debug!("FontList: Couldn't find font family with name={:s}", family_name.to_str());
+            None
+        }
+    }
+
+    fn get_font_template(&mut self, family: &String, desc: &FontTemplateDescriptor) -> Option<Arc<FontTemplateData>> {
+        let transformed_family_name = self.transform_family(family);
+        self.find_font_in_family(&transformed_family_name, desc)
+    }
+
+    fn get_last_resort_template(&mut self, desc: &FontTemplateDescriptor) -> Arc<FontTemplateData> {
+        let last_resort = get_last_resort_font_families();
+
+        for family in last_resort.iter() {
+            let maybe_font_in_family = self.find_font_in_family(family, desc);
+            if maybe_font_in_family.is_some() {
+                return maybe_font_in_family.unwrap();
+            }
+        }
+
+        fail!("Unable to find any fonts that match (do you have fallback fonts installed?)");
+    }
+}
+
+/// The public interface to the font cache task, used exclusively by
+/// the per-thread/task FontContext structures.
+#[deriving(Clone)]
+pub struct FontCacheTask {
+    chan: Sender<Command>,
+}
+
+impl FontCacheTask {
+    pub fn new() -> FontCacheTask {
+        let (chan, port) = channel();
+
+        spawn(proc() {
+            // TODO: Allow users to specify these.
+            let mut generic_fonts = HashMap::with_capacity(5);
+            generic_fonts.insert("serif".to_string(), "Times New Roman".to_string());
+            generic_fonts.insert("sans-serif".to_string(), "Arial".to_string());
+            generic_fonts.insert("cursive".to_string(), "Apple Chancery".to_string());
+            generic_fonts.insert("fantasy".to_string(), "Papyrus".to_string());
+            generic_fonts.insert("monospace".to_string(), "Menlo".to_string());
+
+            let mut cache = FontCache {
+                port: port,
+                generic_fonts: generic_fonts,
+                local_families: HashMap::new(),
+                font_context: FontContextHandle::new(),
+            };
+
+            cache.refresh_local_families();
+            cache.run();
+        });
+
+        FontCacheTask {
+            chan: chan,
+        }
+    }
+
+    pub fn get_font_template(&mut self, family: String, desc: FontTemplateDescriptor)
+                                                -> Arc<FontTemplateData> {
+
+        let (response_chan, response_port) = channel();
+        self.chan.send(GetFontTemplate(family, desc, response_chan));
+
+        let reply = response_port.recv();
+
+        match reply {
+            GetFontTemplateReply(data) => {
+                data
+            }
+        }
+    }
+
+    pub fn exit(&self) {
+        let (response_chan, response_port) = channel();
+        self.chan.send(Exit(response_chan));
+        response_port.recv();
+    }
+}