Auto merge of #19028 - MortimerGoro:webgl2, r=emilio

Kick off WebGL 2.0 implementation

<!-- Please describe your changes on the following line: -->

This PR kicks off the WebGL 2.0 implementation:

- Include WebGL2RenderingContext.webidl and comment unimplemented methods
- Create WebGL2 struct hierarchy with WebGL 1.0 backwards compatibility
- Add WebGL 2.0 entry points to canvas
- Select the correct GL Version on GLContext backends (related PR https://github.com/emilio/rust-offscreen-rendering-context/pull/108)
- Add WebGL version selection in shader compilations
- Create a WebGL 2.0 preference

I tried a complex three.js demo using canvas.getContext("webgl2") and the backwards compatibility worked great.

Next steps:

- I'll add WebGLVersion selection/filtering to WebGLExtensions and move some extensions to core in WebGL 2.0 (e.g. VAOs)
- I'll add the WebGL 2.0 conformance WPT
- I'll create a mega-issue with a the list of all TODO methods for a complete WebGL 2.0 implementation (as @emilio did with WebGL 1.0), so we can start start getting community involvement.

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

<!-- Either: -->
- [ ] There are tests for these changes OR
- [x] These changes do not require tests because I will add the entire webgl 2.0 WPT in a different PR

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1 files changed, 79 insertions, 28 deletions

diff --git a/components/script/dom/htmlcanvaselement.rs b/components/script/dom/htmlcanvaselement.rs
index a44c1fd1fa5..9496670238b 100644
--- a/components/script/dom/htmlcanvaselement.rs
+++ b/components/script/dom/htmlcanvaselement.rs
@@ -4,13 +4,13 @@
 
 use base64;
 use canvas_traits::canvas::{CanvasMsg, FromScriptMsg};
+use canvas_traits::webgl::WebGLVersion;
 use dom::attr::Attr;
 use dom::bindings::cell::DomRefCell;
 use dom::bindings::codegen::Bindings::CanvasRenderingContext2DBinding::CanvasRenderingContext2DMethods;
 use dom::bindings::codegen::Bindings::HTMLCanvasElementBinding;
-use dom::bindings::codegen::Bindings::HTMLCanvasElementBinding::HTMLCanvasElementMethods;
+use dom::bindings::codegen::Bindings::HTMLCanvasElementBinding::{HTMLCanvasElementMethods, RenderingContext};
 use dom::bindings::codegen::Bindings::WebGLRenderingContextBinding::WebGLContextAttributes;
-use dom::bindings::codegen::UnionTypes::CanvasRenderingContext2DOrWebGLRenderingContext;
 use dom::bindings::conversions::ConversionResult;
 use dom::bindings::error::{Error, Fallible};
 use dom::bindings::inheritance::Castable;
@@ -24,6 +24,7 @@ use dom::globalscope::GlobalScope;
 use dom::htmlelement::HTMLElement;
 use dom::node::{Node, window_from_node};
 use dom::virtualmethods::VirtualMethods;
+use dom::webgl2renderingcontext::WebGL2RenderingContext;
 use dom::webglrenderingcontext::{LayoutCanvasWebGLRenderingContextHelpers, WebGLRenderingContext};
 use dom_struct::dom_struct;
 use euclid::Size2D;
@@ -35,6 +36,7 @@ use js::error::throw_type_error;
 use js::jsapi::{HandleValue, JSContext};
 use offscreen_gl_context::GLContextAttributes;
 use script_layout_interface::{HTMLCanvasData, HTMLCanvasDataSource};
+use servo_config::prefs::PREFS;
 use std::iter::repeat;
 use style::attr::{AttrValue, LengthOrPercentageOrAuto};
 
@@ -46,6 +48,7 @@ const DEFAULT_HEIGHT: u32 = 150;
 pub enum CanvasContext {
     Context2d(Dom<CanvasRenderingContext2D>),
     WebGL(Dom<WebGLRenderingContext>),
+    WebGL2(Dom<WebGL2RenderingContext>),
 }
 
 #[dom_struct]
@@ -79,6 +82,7 @@ impl HTMLCanvasElement {
             match *context {
                 CanvasContext::Context2d(ref context) => context.set_bitmap_dimensions(size),
                 CanvasContext::WebGL(ref context) => context.recreate(size),
+                CanvasContext::WebGL2(ref context) => context.recreate(size),
             }
         }
     }
@@ -113,6 +117,9 @@ impl LayoutHTMLCanvasElementHelpers for LayoutDom<HTMLCanvasElement> {
                 Some(&CanvasContext::WebGL(ref context)) => {
                     context.to_layout().canvas_data_source()
                 },
+                Some(&CanvasContext::WebGL2(ref context)) => {
+                    context.to_layout().canvas_data_source()
+                },
                 None => {
                     HTMLCanvasDataSource::Image(None)
                 }
@@ -165,32 +172,16 @@ impl HTMLCanvasElement {
         }
     }
 
-    #[allow(unsafe_code)]
-    pub fn get_or_init_webgl_context(&self,
-                                 cx: *mut JSContext,
-                                 attrs: Option<HandleValue>) -> Option<DomRoot<WebGLRenderingContext>> {
+    pub fn get_or_init_webgl_context(
+        &self,
+        cx: *mut JSContext,
+        attrs: Option<HandleValue>
+    ) -> Option<DomRoot<WebGLRenderingContext>> {
         if self.context.borrow().is_none() {
             let window = window_from_node(self);
             let size = self.get_size();
-
-            let attrs = if let Some(webgl_attributes) = attrs {
-                match unsafe {
-                    WebGLContextAttributes::new(cx, webgl_attributes) } {
-                    Ok(ConversionResult::Success(ref attrs)) => From::from(attrs),
-                    Ok(ConversionResult::Failure(ref error)) => {
-                        unsafe { throw_type_error(cx, &error); }
-                        return None;
-                    }
-                    _ => {
-                        debug!("Unexpected error on conversion of WebGLContextAttributes");
-                        return None;
-                    }
-                }
-            } else {
-                GLContextAttributes::default()
-            };
-
-            let maybe_ctx = WebGLRenderingContext::new(&window, self, size, attrs);
+            let attrs = Self::get_gl_attributes(cx, attrs)?;
+            let maybe_ctx = WebGLRenderingContext::new(&window, self, WebGLVersion::WebGL1, size, attrs);
 
             *self.context.borrow_mut() = maybe_ctx.map( |ctx| CanvasContext::WebGL(Dom::from_ref(&*ctx)));
         }
@@ -202,6 +193,58 @@ impl HTMLCanvasElement {
         }
     }
 
+    pub fn get_or_init_webgl2_context(
+        &self,
+        cx: *mut JSContext,
+        attrs: Option<HandleValue>
+    ) -> Option<DomRoot<WebGL2RenderingContext>> {
+        if !PREFS.is_webgl2_enabled() {
+            return None
+        }
+        if self.context.borrow().is_none() {
+            let window = window_from_node(self);
+            let size = self.get_size();
+            let attrs = Self::get_gl_attributes(cx, attrs)?;
+            let maybe_ctx = WebGL2RenderingContext::new(&window, self, size, attrs);
+
+            *self.context.borrow_mut() = maybe_ctx.map( |ctx| CanvasContext::WebGL2(Dom::from_ref(&*ctx)));
+        }
+
+        if let Some(CanvasContext::WebGL2(ref context)) = *self.context.borrow() {
+            Some(DomRoot::from_ref(&*context))
+        } else {
+            None
+        }
+    }
+
+    /// Gets the base WebGLRenderingContext for WebGL or WebGL 2, if exists.
+    pub fn get_base_webgl_context(&self) -> Option<DomRoot<WebGLRenderingContext>> {
+        match *self.context.borrow() {
+            Some(CanvasContext::WebGL(ref context)) => Some(DomRoot::from_ref(&*context)),
+            Some(CanvasContext::WebGL2(ref context)) => Some(context.base_context()),
+            _ => None
+        }
+    }
+
+    #[allow(unsafe_code)]
+    fn get_gl_attributes(cx: *mut JSContext, attrs: Option<HandleValue>) -> Option<GLContextAttributes> {
+        let webgl_attributes = match attrs {
+            Some(attrs) => attrs,
+            None => return Some(GLContextAttributes::default()),
+        };
+        match unsafe { WebGLContextAttributes::new(cx, webgl_attributes) } {
+            Ok(ConversionResult::Success(ref attrs)) => Some(From::from(attrs)),
+            Ok(ConversionResult::Failure(ref error)) => {
+                unsafe { throw_type_error(cx, &error); }
+                None
+            }
+            _ => {
+                debug!("Unexpected error on conversion of WebGLContextAttributes");
+                None
+            }
+        }
+    }
+
     pub fn is_valid(&self) -> bool {
         self.Height() != 0 && self.Width() != 0
     }
@@ -225,6 +268,10 @@ impl HTMLCanvasElement {
                 // TODO: add a method in WebGLRenderingContext to get the pixels.
                 return None;
             },
+            Some(&CanvasContext::WebGL2(_)) => {
+                // TODO: add a method in WebGL2RenderingContext to get the pixels.
+                return None;
+            },
             None => {
                 repeat(0xffu8).take((size.height as usize) * (size.width as usize) * 4).collect()
             }
@@ -253,15 +300,19 @@ impl HTMLCanvasElementMethods for HTMLCanvasElement {
                   cx: *mut JSContext,
                   id: DOMString,
                   attributes: Vec<HandleValue>)
-        -> Option<CanvasRenderingContext2DOrWebGLRenderingContext> {
+        -> Option<RenderingContext> {
         match &*id {
             "2d" => {
                 self.get_or_init_2d_context()
-                    .map(CanvasRenderingContext2DOrWebGLRenderingContext::CanvasRenderingContext2D)
+                    .map(RenderingContext::CanvasRenderingContext2D)
             }
             "webgl" | "experimental-webgl" => {
                 self.get_or_init_webgl_context(cx, attributes.get(0).cloned())
-                    .map(CanvasRenderingContext2DOrWebGLRenderingContext::WebGLRenderingContext)
+                    .map(RenderingContext::WebGLRenderingContext)
+            }
+            "webgl2" | "experimental-webgl2" => {
+                self.get_or_init_webgl2_context(cx, attributes.get(0).cloned())
+                    .map(RenderingContext::WebGL2RenderingContext)
             }
             _ => None
         }