servo: Merge #5414 - Canvas: added arcTo() support (from mmatyas:canvas_arcto); r=jdm

Based on the implementation in Firefox.

After comparing how `arcTo` works in different browsers, I've found the code in Firefox the cleanest implentation. It also performed better on some test, for example the one on [this site](http://flashcanvas.net/examples/dl.dropbox.com/u/1865210/mindcat/arcto.html). In (Linux) Firefox 36, it looks like [this](http://i59.tinypic.com/2ch5b2d.png), while in Chromium 41, [some features are missing](http://i58.tinypic.com/30u5w8z.png).

Source-Repo: https://github.com/servo/servo
Source-Revision: ae31d9d9e86eb90a1fe2858f10ca5e6e2e722c67

servo/components/canvas/canvas_paint_task.rs

@@ -16,6 +16,7 @@ use util::vec::byte_swap;
 
 use cssparser::RGBA;
 use std::borrow::ToOwned;
+use std::num::Float;
 use std::sync::mpsc::{channel, Sender};
 
 #[derive(Clone)]
@@ -34,6 +35,7 @@ pub enum CanvasMsg {
     QuadraticCurveTo(Point2D<f32>, Point2D<f32>),
     BezierCurveTo(Point2D<f32>, Point2D<f32>, Point2D<f32>),
     Arc(Point2D<f32>, f32, f32, f32, bool),
+    ArcTo(Point2D<f32>, Point2D<f32>, f32),
     SetFillStyle(FillOrStrokeStyle),
     SetStrokeStyle(FillOrStrokeStyle),
     SetTransform(Matrix2D<f32>),
@@ -230,6 +232,9 @@ impl<'a> CanvasPaintTask<'a> {
                     CanvasMsg::Arc(ref center, radius, start, end, ccw) => {
                         painter.arc(center, radius, start, end, ccw)
                     }
+                    CanvasMsg::ArcTo(ref cp1, ref cp2, radius) => {
+                        painter.arc_to(cp1, cp2, radius)
+                    }
                     CanvasMsg::SetFillStyle(style) => painter.set_fill_style(style),
                     CanvasMsg::SetStrokeStyle(style) => painter.set_stroke_style(style),
                     CanvasMsg::SetTransform(ref matrix) => painter.set_transform(matrix),
@@ -344,6 +349,61 @@ impl<'a> CanvasPaintTask<'a> {
         self.path_builder.arc(*center, radius, start_angle, end_angle, ccw)
     }
 
+    fn arc_to(&self,
+              cp1: &Point2D<AzFloat>,
+              cp2: &Point2D<AzFloat>,
+              radius: AzFloat) {
+        let cp0 = self.path_builder.get_current_point();
+        let cp1 = *cp1;
+        let cp2 = *cp2;
+
+        if (cp0.x == cp1.x && cp0.y == cp1.y) || cp1 == cp2 || radius == 0.0 {
+            self.line_to(&cp1);
+            return;
+        }
+
+        // if all three control points lie on a single straight line,
+        // connect the first two by a straight line
+        let direction = (cp2.x - cp1.x) * (cp0.y - cp1.y) + (cp2.y - cp1.y) * (cp1.x - cp0.x);
+        if direction == 0.0 {
+            self.line_to(&cp1);
+            return;
+        }
+
+        // otherwise, draw the Arc
+        let a2 = (cp0.x - cp1.x).powi(2) + (cp0.y - cp1.y).powi(2);
+        let b2 = (cp1.x - cp2.x).powi(2) + (cp1.y - cp2.y).powi(2);
+        let d = {
+            let c2 = (cp0.x - cp2.x).powi(2) + (cp0.y - cp2.y).powi(2);
+            let cosx = (a2 + b2 - c2) / (2.0 * (a2 * b2).sqrt());
+            let sinx = (1.0 - cosx.powi(2)).sqrt();
+            radius / ((1.0 - cosx) / sinx)
+        };
+
+        // first tangent point
+        let anx = (cp1.x - cp0.x) / a2.sqrt();
+        let any = (cp1.y - cp0.y) / a2.sqrt();
+        let tp1 = Point2D::<AzFloat>(cp1.x - anx * d, cp1.y - any * d);
+
+        // second tangent point
+        let bnx = (cp1.x - cp2.x) / b2.sqrt();
+        let bny = (cp1.y - cp2.y) / b2.sqrt();
+        let tp2 = Point2D::<AzFloat>(cp1.x - bnx * d, cp1.y - bny * d);
+
+        // arc center and angles
+        let anticlockwise = direction < 0.0;
+        let cx = tp1.x + any * radius * if anticlockwise { 1.0 } else { -1.0 };
+        let cy = tp1.y - anx * radius * if anticlockwise { 1.0 } else { -1.0 };
+        let angle_start = (tp1.y - cy).atan2(tp1.x - cx);
+        let angle_end = (tp2.y - cy).atan2(tp2.x - cx);
+
+        self.line_to(&tp1);
+        if [cx, cy, angle_start, angle_end].iter().all(|x| x.is_finite()) {
+            self.arc(&Point2D::<AzFloat>(cx, cy), radius,
+                     angle_start, angle_end, anticlockwise);
+        }
+    }
+
     fn set_fill_style(&mut self, style: FillOrStrokeStyle) {
         self.fill_style = style.to_azure_pattern(&self.drawtarget)
     }

servo/components/canvas/lib.rs

@@ -3,6 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #![feature(collections)]
+#![feature(std_misc)]
 
 extern crate azure;
 extern crate cssparser;

servo/components/script/dom/canvasrenderingcontext2d.rs

@@ -477,6 +477,19 @@ impl<'a> CanvasRenderingContext2DMethods for JSRef<'a, CanvasRenderingContext2D>
         Ok(())
     }
 
+    fn ArcTo(self, cp1x: f64, cp1y: f64, cp2x: f64, cp2y: f64, r: f64) -> Fallible<()> {
+        if !([cp1x, cp1y, cp2x, cp2y, r].iter().all(|x| x.is_finite())) {
+            return Ok(());
+        }
+        if r < 0.0 {
+            return Err(IndexSize);
+        }
+        self.renderer.send(CanvasMsg::ArcTo(Point2D(cp1x as f32, cp1y as f32),
+                                            Point2D(cp2x as f32, cp2y as f32),
+                                            r as f32)).unwrap();
+        Ok(())
+    }
+
     // https://html.spec.whatwg.org/#dom-context-2d-imagesmoothingenabled
     fn ImageSmoothingEnabled(self) -> bool {
         self.image_smoothing_enabled.get()

servo/components/script/dom/webidls/CanvasRenderingContext2D.webidl

@@ -145,7 +145,10 @@ interface CanvasPathMethods {
                      unrestricted double x,
                      unrestricted double y);
 
-  //void arcTo(double x1, double y1, double x2, double y2, double radius);
+  [Throws]
+  void arcTo(unrestricted double x1, unrestricted double y1,
+             unrestricted double x2, unrestricted double y2,
+             unrestricted double radius);
 // NOT IMPLEMENTED  [LenientFloat] void arcTo(double x1, double y1, double x2, double y2, double radiusX, double radiusY, double rotation);
 
   //void rect(double x, double y, double w, double h);

servo/components/servo/Cargo.lock

@@ -31,7 +31,7 @@ source = "git+https://github.com/tomaka/android-rs-glue#5a68056599fb498b0cf3715f
 [[package]]
 name = "azure"
 version = "0.1.0"
-source = "git+https://github.com/servo/rust-azure#9aae2113fb19a34a67a82b7ec6a5e0b34e290d29"
+source = "git+https://github.com/servo/rust-azure#c71473d94ae24fb195987660698207d5088a4042"
 dependencies = [
  "core_foundation 0.1.0 (git+https://github.com/servo/rust-core-foundation)",
  "core_graphics 0.1.0 (git+https://github.com/servo/rust-core-graphics)",

servo/ports/cef/Cargo.lock

@@ -36,7 +36,7 @@ source = "git+https://github.com/tomaka/android-rs-glue#5a68056599fb498b0cf3715f
 [[package]]
 name = "azure"
 version = "0.1.0"
-source = "git+https://github.com/servo/rust-azure#9aae2113fb19a34a67a82b7ec6a5e0b34e290d29"
+source = "git+https://github.com/servo/rust-azure#c71473d94ae24fb195987660698207d5088a4042"
 dependencies = [
  "core_foundation 0.1.0 (git+https://github.com/servo/rust-core-foundation)",
  "core_graphics 0.1.0 (git+https://github.com/servo/rust-core-graphics)",

servo/ports/gonk/Cargo.lock

@@ -24,7 +24,7 @@ dependencies = [
 [[package]]
 name = "azure"
 version = "0.1.0"
-source = "git+https://github.com/servo/rust-azure#9aae2113fb19a34a67a82b7ec6a5e0b34e290d29"
+source = "git+https://github.com/servo/rust-azure#c71473d94ae24fb195987660698207d5088a4042"
 dependencies = [
  "core_foundation 0.1.0 (git+https://github.com/servo/rust-core-foundation)",
  "core_graphics 0.1.0 (git+https://github.com/servo/rust-core-graphics)",