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/canvas/canvas_paint_thread.rs

@@ -7,6 +7,7 @@ use canvas_traits::canvas::*;
 use canvas_traits::ConstellationCanvasMsg;
 use crossbeam_channel::{select, unbounded, Sender};
 use euclid::default::Size2D;
+use gfx::font_cache_thread::FontCacheThread;
 use ipc_channel::ipc::{self, IpcSender};
 use ipc_channel::router::ROUTER;
 use std::borrow::ToOwned;
@@ -35,14 +36,19 @@ pub struct CanvasPaintThread<'a> {
     canvases: HashMap<CanvasId, CanvasData<'a>>,
     next_canvas_id: CanvasId,
     webrender_api: Box<dyn WebrenderApi>,
+    font_cache_thread: FontCacheThread,
 }
 
 impl<'a> CanvasPaintThread<'a> {
-    fn new(webrender_api: Box<dyn WebrenderApi>) -> CanvasPaintThread<'a> {
+    fn new(
+        webrender_api: Box<dyn WebrenderApi>,
+        font_cache_thread: FontCacheThread,
+    ) -> CanvasPaintThread<'a> {
         CanvasPaintThread {
             canvases: HashMap::new(),
             next_canvas_id: CanvasId(0),
             webrender_api,
+            font_cache_thread,
         }
     }
 
@@ -50,6 +56,7 @@ impl<'a> CanvasPaintThread<'a> {
     /// communicate with it.
     pub fn start(
         webrender_api: Box<dyn WebrenderApi + Send>,
+        font_cache_thread: FontCacheThread,
     ) -> (Sender<ConstellationCanvasMsg>, IpcSender<CanvasMsg>) {
         let (ipc_sender, ipc_receiver) = ipc::channel::<CanvasMsg>().unwrap();
         let msg_receiver = ROUTER.route_ipc_receiver_to_new_crossbeam_receiver(ipc_receiver);
@@ -57,7 +64,7 @@ impl<'a> CanvasPaintThread<'a> {
         thread::Builder::new()
             .name("CanvasThread".to_owned())
             .spawn(move || {
-                let mut canvas_paint_thread = CanvasPaintThread::new(webrender_api);
+                let mut canvas_paint_thread = CanvasPaintThread::new(webrender_api, font_cache_thread);
                 loop {
                     select! {
                         recv(msg_receiver) -> msg => {
@@ -118,6 +125,8 @@ impl<'a> CanvasPaintThread<'a> {
             AntialiasMode::None
         };
 
+        let font_cache_thread = self.font_cache_thread.clone();
+
         let canvas_id = self.next_canvas_id.clone();
         self.next_canvas_id.0 += 1;
 
@@ -125,7 +134,7 @@ impl<'a> CanvasPaintThread<'a> {
             size,
             self.webrender_api.clone(),
             antialias,
-            canvas_id.clone(),
+            font_cache_thread,
         );
         self.canvases.insert(canvas_id.clone(), canvas_data);
 
@@ -134,9 +143,10 @@ impl<'a> CanvasPaintThread<'a> {
 
     fn process_canvas_2d_message(&mut self, message: Canvas2dMsg, canvas_id: CanvasId) {
         match message {
-            Canvas2dMsg::FillText(text, x, y, max_width, style) => {
+            Canvas2dMsg::FillText(text, x, y, max_width, style, is_rtl) => {
                 self.canvas(canvas_id).set_fill_style(style);
-                self.canvas(canvas_id).fill_text(text, x, y, max_width);
+                self.canvas(canvas_id)
+                    .fill_text(text, x, y, max_width, is_rtl);
             },
             Canvas2dMsg::FillRect(rect, style) => {
                 self.canvas(canvas_id).set_fill_style(style);
@@ -247,6 +257,13 @@ impl<'a> CanvasPaintThread<'a> {
             },
             Canvas2dMsg::SetShadowBlur(value) => self.canvas(canvas_id).set_shadow_blur(value),
             Canvas2dMsg::SetShadowColor(color) => self.canvas(canvas_id).set_shadow_color(color),
+            Canvas2dMsg::SetFont(font_style) => self.canvas(canvas_id).set_font(font_style),
+            Canvas2dMsg::SetTextAlign(text_align) => {
+                self.canvas(canvas_id).set_text_align(text_align)
+            },
+            Canvas2dMsg::SetTextBaseline(text_baseline) => {
+                self.canvas(canvas_id).set_text_baseline(text_baseline)
+            },
         }
     }