Auto merge of #24261 - paulrouget:fakeMeasureTExt, r=jdm

Temporary implementation of Canvas.MeasureText

@jdm: that will help with the babylonjs demos. Another approach is to implement that in JS and add it to the demos.

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/24261)
<!-- Reviewable:end -->

6 files changed, 205 insertions, 1 deletions

diff --git a/components/script/dom/canvasrenderingcontext2d.rs b/components/script/dom/canvasrenderingcontext2d.rs
index 2a8f14295c0..1faf9878b53 100644
--- a/components/script/dom/canvasrenderingcontext2d.rs
+++ b/components/script/dom/canvasrenderingcontext2d.rs
@@ -24,6 +24,7 @@ use crate::dom::globalscope::GlobalScope;
 use crate::dom::htmlcanvaselement::{CanvasContext, HTMLCanvasElement};
 use crate::dom::imagedata::ImageData;
 use crate::dom::node::{Node, NodeDamage};
+use crate::dom::textmetrics::TextMetrics;
 use crate::unpremultiplytable::UNPREMULTIPLY_TABLE;
 use canvas_traits::canvas::{Canvas2dMsg, CanvasId, CanvasMsg};
 use canvas_traits::canvas::{CompositionOrBlending, FillOrStrokeStyle, FillRule};
@@ -873,6 +874,15 @@ impl CanvasState {
         self.send_canvas_2d_msg(Canvas2dMsg::FillText(parsed_text, x, y, max_width));
     }
 
+    // https://html.spec.whatwg.org/multipage/#textmetrics
+    pub fn MeasureText(&self, global: &GlobalScope, _text: DOMString) -> DomRoot<TextMetrics> {
+        // FIXME: for now faking the implementation of MeasureText().
+        // See https://github.com/servo/servo/issues/5411#issuecomment-533776291
+        TextMetrics::new(
+            global, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
+        )
+    }
+
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-linewidth
     pub fn LineWidth(&self) -> f64 {
         self.state.borrow().line_width
@@ -1671,6 +1681,11 @@ impl CanvasRenderingContext2DMethods for CanvasRenderingContext2D {
         self.mark_as_dirty();
     }
 
+    // https://html.spec.whatwg.org/multipage/#textmetrics
+    fn MeasureText(&self, text: DOMString) -> DomRoot<TextMetrics> {
+        self.canvas_state.borrow().MeasureText(&self.global(), text)
+    }
+
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-drawimage
     fn DrawImage(&self, image: CanvasImageSource, dx: f64, dy: f64) -> ErrorResult {
         self.canvas_state
diff --git a/components/script/dom/mod.rs b/components/script/dom/mod.rs
index 34777a20fe0..d698fcc709f 100644
--- a/components/script/dom/mod.rs
+++ b/components/script/dom/mod.rs
@@ -484,6 +484,7 @@ pub mod text;
 pub mod textcontrol;
 pub mod textdecoder;
 pub mod textencoder;
+pub mod textmetrics;
 pub mod texttrack;
 pub mod texttrackcue;
 pub mod texttrackcuelist;
diff --git a/components/script/dom/offscreencanvasrenderingcontext2d.rs b/components/script/dom/offscreencanvasrenderingcontext2d.rs
index 461af3b882f..d18cd00df54 100644
--- a/components/script/dom/offscreencanvasrenderingcontext2d.rs
+++ b/components/script/dom/offscreencanvasrenderingcontext2d.rs
@@ -23,6 +23,7 @@ use crate::dom::globalscope::GlobalScope;
 use crate::dom::htmlcanvaselement::HTMLCanvasElement;
 use crate::dom::imagedata::ImageData;
 use crate::dom::offscreencanvas::OffscreenCanvas;
+use crate::dom::textmetrics::TextMetrics;
 use dom_struct::dom_struct;
 use euclid::default::Size2D;
 
@@ -244,6 +245,11 @@ impl OffscreenCanvasRenderingContext2DMethods for OffscreenCanvasRenderingContex
         self.canvas_state.borrow().FillText(text, x, y, max_width)
     }
 
+    // https://html.spec.whatwg.org/multipage/#textmetrics
+    fn MeasureText(&self, text: DOMString) -> DomRoot<TextMetrics> {
+        self.canvas_state.borrow().MeasureText(&self.global(), text)
+    }
+
     // https://html.spec.whatwg.org/multipage/#dom-context-2d-linewidth
     fn LineWidth(&self) -> f64 {
         self.canvas_state.borrow().LineWidth()
diff --git a/components/script/dom/textmetrics.rs b/components/script/dom/textmetrics.rs
new file mode 100644
index 00000000000..867071bd0aa
--- /dev/null
+++ b/components/script/dom/textmetrics.rs
@@ -0,0 +1,158 @@
+/* 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 https://mozilla.org/MPL/2.0/. */
+
+use crate::dom::bindings::codegen::Bindings::TextMetricsBinding;
+use crate::dom::bindings::codegen::Bindings::TextMetricsBinding::TextMetricsMethods;
+use crate::dom::bindings::num::Finite;
+use crate::dom::bindings::reflector::{reflect_dom_object, Reflector};
+use crate::dom::bindings::root::DomRoot;
+use crate::dom::globalscope::GlobalScope;
+use dom_struct::dom_struct;
+
+#[dom_struct]
+pub struct TextMetrics {
+    reflector_: Reflector,
+    width: Finite<f64>,
+    actualBoundingBoxLeft: Finite<f64>,
+    actualBoundingBoxRight: Finite<f64>,
+    fontBoundingBoxAscent: Finite<f64>,
+    fontBoundingBoxDescent: Finite<f64>,
+    actualBoundingBoxAscent: Finite<f64>,
+    actualBoundingBoxDescent: Finite<f64>,
+    emHeightAscent: Finite<f64>,
+    emHeightDescent: Finite<f64>,
+    hangingBaseline: Finite<f64>,
+    alphabeticBaseline: Finite<f64>,
+    ideographicBaseline: Finite<f64>,
+}
+
+impl TextMetrics {
+    fn new_inherited(
+        width: f64,
+        actualBoundingBoxLeft: f64,
+        actualBoundingBoxRight: f64,
+        fontBoundingBoxAscent: f64,
+        fontBoundingBoxDescent: f64,
+        actualBoundingBoxAscent: f64,
+        actualBoundingBoxDescent: f64,
+        emHeightAscent: f64,
+        emHeightDescent: f64,
+        hangingBaseline: f64,
+        alphabeticBaseline: f64,
+        ideographicBaseline: f64,
+    ) -> TextMetrics {
+        TextMetrics {
+            reflector_: Reflector::new(),
+            width: Finite::wrap(width),
+            actualBoundingBoxLeft: Finite::wrap(actualBoundingBoxLeft),
+            actualBoundingBoxRight: Finite::wrap(actualBoundingBoxRight),
+            fontBoundingBoxAscent: Finite::wrap(fontBoundingBoxAscent),
+            fontBoundingBoxDescent: Finite::wrap(fontBoundingBoxDescent),
+            actualBoundingBoxAscent: Finite::wrap(actualBoundingBoxAscent),
+            actualBoundingBoxDescent: Finite::wrap(actualBoundingBoxDescent),
+            emHeightAscent: Finite::wrap(emHeightAscent),
+            emHeightDescent: Finite::wrap(emHeightDescent),
+            hangingBaseline: Finite::wrap(hangingBaseline),
+            alphabeticBaseline: Finite::wrap(alphabeticBaseline),
+            ideographicBaseline: Finite::wrap(ideographicBaseline),
+        }
+    }
+
+    pub fn new(
+        global: &GlobalScope,
+        width: f64,
+        actualBoundingBoxLeft: f64,
+        actualBoundingBoxRight: f64,
+        fontBoundingBoxAscent: f64,
+        fontBoundingBoxDescent: f64,
+        actualBoundingBoxAscent: f64,
+        actualBoundingBoxDescent: f64,
+        emHeightAscent: f64,
+        emHeightDescent: f64,
+        hangingBaseline: f64,
+        alphabeticBaseline: f64,
+        ideographicBaseline: f64,
+    ) -> DomRoot<TextMetrics> {
+        reflect_dom_object(
+            Box::new(TextMetrics::new_inherited(
+                width,
+                actualBoundingBoxLeft,
+                actualBoundingBoxRight,
+                fontBoundingBoxAscent,
+                fontBoundingBoxDescent,
+                actualBoundingBoxAscent,
+                actualBoundingBoxDescent,
+                emHeightAscent,
+                emHeightDescent,
+                hangingBaseline,
+                alphabeticBaseline,
+                ideographicBaseline,
+            )),
+            global,
+            TextMetricsBinding::Wrap,
+        )
+    }
+}
+
+impl TextMetricsMethods for TextMetrics {
+    /// https://html.spec.whatwg.org/multipage/#dom-textmetrics-width
+    fn Width(&self) -> Finite<f64> {
+        self.width
+    }
+
+    /// https://html.spec.whatwg.org/multipage/#dom-textmetrics-actualboundingboxleft
+    fn ActualBoundingBoxLeft(&self) -> Finite<f64> {
+        self.actualBoundingBoxLeft
+    }
+
+    /// https://html.spec.whatwg.org/multipage/#dom-textmetrics-actualboundingboxright
+    fn ActualBoundingBoxRight(&self) -> Finite<f64> {
+        self.actualBoundingBoxRight
+    }
+
+    /// https://html.spec.whatwg.org/multipage/#dom-textmetrics-fontboundingboxascent
+    fn FontBoundingBoxAscent(&self) -> Finite<f64> {
+        self.fontBoundingBoxAscent
+    }
+
+    /// https://html.spec.whatwg.org/multipage/#dom-textmetrics-fontboundingboxascent
+    fn FontBoundingBoxDescent(&self) -> Finite<f64> {
+        self.fontBoundingBoxDescent
+    }
+
+    /// https://html.spec.whatwg.org/multipage/#dom-textmetrics-actualboundingboxascent
+    fn ActualBoundingBoxAscent(&self) -> Finite<f64> {
+        self.actualBoundingBoxAscent
+    }
+
+    /// https://html.spec.whatwg.org/multipage/#dom-textmetrics-actualboundingboxdescent
+    fn ActualBoundingBoxDescent(&self) -> Finite<f64> {
+        self.actualBoundingBoxDescent
+    }
+
+    /// https://html.spec.whatwg.org/multipage/#dom-textmetrics-emheightascent
+    fn EmHeightAscent(&self) -> Finite<f64> {
+        self.emHeightAscent
+    }
+
+    /// https://html.spec.whatwg.org/multipage/#dom-textmetrics-emheightdescent
+    fn EmHeightDescent(&self) -> Finite<f64> {
+        self.emHeightDescent
+    }
+
+    /// https://html.spec.whatwg.org/multipage/#dom-textmetrics-hangingbaseline
+    fn HangingBaseline(&self) -> Finite<f64> {
+        self.hangingBaseline
+    }
+
+    /// https://html.spec.whatwg.org/multipage/#dom-textmetrics-alphabeticbaseline
+    fn AlphabeticBaseline(&self) -> Finite<f64> {
+        self.alphabeticBaseline
+    }
+
+    /// https://html.spec.whatwg.org/multipage/#dom-textmetrics-ideographicbaseline
+    fn IdeographicBaseline(&self) -> Finite<f64> {
+        self.ideographicBaseline
+    }
+}
diff --git a/components/script/dom/webidls/CanvasRenderingContext2D.webidl b/components/script/dom/webidls/CanvasRenderingContext2D.webidl
index 92e8b80d5ef..2da0372a9ba 100644
--- a/components/script/dom/webidls/CanvasRenderingContext2D.webidl
+++ b/components/script/dom/webidls/CanvasRenderingContext2D.webidl
@@ -153,7 +153,8 @@ interface CanvasText {
                 optional unrestricted double maxWidth);
   //void strokeText(DOMString text, unrestricted double x, unrestricted double y,
   //                optional unrestricted double maxWidth);
-  //TextMetrics measureText(DOMString text);
+  [Pref="dom.canvas-text.enabled"]
+  TextMetrics measureText(DOMString text);
 };
 
 [Exposed=(PaintWorklet, Window, Worker), NoInterfaceObject]
diff --git a/components/script/dom/webidls/TextMetrics.webidl b/components/script/dom/webidls/TextMetrics.webidl
new file mode 100644
index 00000000000..f3d90450824
--- /dev/null
+++ b/components/script/dom/webidls/TextMetrics.webidl
@@ -0,0 +1,23 @@
+/* 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 https://mozilla.org/MPL/2.0/. */
+
+// https://html.spec.whatwg.org/multipage/#textmetrics
+[Exposed=(PaintWorklet, Window, Worker), Pref="dom.canvas-text.enabled"]
+interface TextMetrics {
+  // x-direction
+  readonly attribute double width; // advance width
+  readonly attribute double actualBoundingBoxLeft;
+  readonly attribute double actualBoundingBoxRight;
+
+  // y-direction
+  readonly attribute double fontBoundingBoxAscent;
+  readonly attribute double fontBoundingBoxDescent;
+  readonly attribute double actualBoundingBoxAscent;
+  readonly attribute double actualBoundingBoxDescent;
+  readonly attribute double emHeightAscent;
+  readonly attribute double emHeightDescent;
+  readonly attribute double hangingBaseline;
+  readonly attribute double alphabeticBaseline;
+  readonly attribute double ideographicBaseline;
+};