Initial implementation of WebGLQueries

This patch adds initial support for WeGLQueries. Most related WebGL
functions and objects are implemented [1]. What's still missing is
the `EXT_disjoint_timer_query_webgl2` support.

[1]: https://www.khronos.org/registry/webgl/specs/latest/2.0/#3.7.12

components/script/dom/webglquery.rs

@@ -0,0 +1,194 @@
+/* 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::WebGL2RenderingContextBinding::WebGL2RenderingContextConstants as constants;
+use crate::dom::bindings::codegen::Bindings::WebGLQueryBinding;
+use crate::dom::bindings::inheritance::Castable;
+use crate::dom::bindings::refcounted::Trusted;
+use crate::dom::bindings::reflector::{reflect_dom_object, DomObject};
+use crate::dom::bindings::root::DomRoot;
+use crate::dom::webglobject::WebGLObject;
+use crate::dom::webglrenderingcontext::WebGLRenderingContext;
+use crate::task_source::TaskSource;
+use canvas_traits::webgl::WebGLError::*;
+use canvas_traits::webgl::{webgl_channel, WebGLCommand, WebGLQueryId};
+use dom_struct::dom_struct;
+use std::cell::Cell;
+
+#[dom_struct]
+pub struct WebGLQuery {
+    webgl_object: WebGLObject,
+    gl_id: WebGLQueryId,
+    gl_target: Cell<Option<u32>>,
+    marked_for_deletion: Cell<bool>,
+    query_result_available: Cell<Option<u32>>,
+    query_result: Cell<u32>,
+}
+
+impl WebGLQuery {
+    fn new_inherited(context: &WebGLRenderingContext, id: WebGLQueryId) -> Self {
+        Self {
+            webgl_object: WebGLObject::new_inherited(context),
+            gl_id: id,
+            gl_target: Cell::new(None),
+            marked_for_deletion: Cell::new(false),
+            query_result_available: Cell::new(None),
+            query_result: Cell::new(0),
+        }
+    }
+
+    pub fn new(context: &WebGLRenderingContext) -> DomRoot<Self> {
+        let (sender, receiver) = webgl_channel().unwrap();
+        context.send_command(WebGLCommand::GenerateQuery(sender));
+        let id = receiver.recv().unwrap();
+
+        reflect_dom_object(
+            Box::new(Self::new_inherited(context, id)),
+            &*context.global(),
+            WebGLQueryBinding::Wrap,
+        )
+    }
+
+    pub fn begin(
+        &self,
+        context: &WebGLRenderingContext,
+        target: u32,
+    ) -> Result<(), canvas_traits::webgl::WebGLError> {
+        if self.marked_for_deletion.get() {
+            return Err(InvalidOperation);
+        }
+        if let Some(current_target) = self.gl_target.get() {
+            if current_target != target {
+                return Err(InvalidOperation);
+            }
+        }
+        match target {
+            constants::ANY_SAMPLES_PASSED |
+            constants::ANY_SAMPLES_PASSED_CONSERVATIVE |
+            constants::TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN => (),
+            _ => return Err(InvalidEnum),
+        }
+        self.gl_target.set(Some(target));
+
+        context.send_command(WebGLCommand::BeginQuery(target, self.gl_id));
+        Ok(())
+    }
+
+    pub fn end(
+        &self,
+        context: &WebGLRenderingContext,
+        target: u32,
+    ) -> Result<(), canvas_traits::webgl::WebGLError> {
+        if self.marked_for_deletion.get() {
+            return Err(InvalidOperation);
+        }
+        if let Some(current_target) = self.gl_target.get() {
+            if current_target != target {
+                return Err(InvalidOperation);
+            }
+        }
+        match target {
+            constants::ANY_SAMPLES_PASSED |
+            constants::ANY_SAMPLES_PASSED_CONSERVATIVE |
+            constants::TRANSFORM_FEEDBACK_PRIMITIVES_WRITTEN => (),
+            _ => return Err(InvalidEnum),
+        }
+        context.send_command(WebGLCommand::EndQuery(target));
+        Ok(())
+    }
+
+    pub fn delete(&self, fallible: bool) {
+        if !self.marked_for_deletion.get() {
+            self.marked_for_deletion.set(true);
+
+            let context = self.upcast::<WebGLObject>().context();
+            let command = WebGLCommand::DeleteQuery(self.gl_id);
+            if fallible {
+                context.send_command_ignored(command);
+            } else {
+                context.send_command(command);
+            }
+        }
+    }
+
+    pub fn is_valid(&self) -> bool {
+        !self.marked_for_deletion.get() && self.target().is_some()
+    }
+
+    pub fn target(&self) -> Option<u32> {
+        self.gl_target.get()
+    }
+
+    fn update_results(&self, context: &WebGLRenderingContext) {
+        let (sender, receiver) = webgl_channel().unwrap();
+        context.send_command(WebGLCommand::GetQueryState(
+            sender,
+            self.gl_id,
+            constants::QUERY_RESULT_AVAILABLE,
+        ));
+        let is_available = receiver.recv().unwrap();
+        if is_available == 0 {
+            self.query_result_available.set(None);
+            return;
+        }
+
+        let (sender, receiver) = webgl_channel().unwrap();
+        context.send_command(WebGLCommand::GetQueryState(
+            sender,
+            self.gl_id,
+            constants::QUERY_RESULT,
+        ));
+
+        self.query_result.set(receiver.recv().unwrap());
+        self.query_result_available.set(Some(is_available));
+    }
+
+    #[cfg_attr(rustfmt, rustfmt_skip)]
+    pub fn get_parameter(
+        &self,
+        context: &WebGLRenderingContext,
+        pname: u32,
+    ) -> Result<u32, canvas_traits::webgl::WebGLError> {
+        if !self.is_valid() {
+            return Err(InvalidOperation);
+        }
+        match pname {
+            constants::QUERY_RESULT |
+            constants::QUERY_RESULT_AVAILABLE => {},
+            _ => return Err(InvalidEnum),
+        }
+
+        if self.query_result_available.get().is_none() {
+            self.query_result_available.set(Some(0));
+
+            let this = Trusted::new(self);
+            let context = Trusted::new(context);
+            let task = task!(request_query_state: move || {
+                let this = this.root();
+                let context = context.root();
+                this.update_results(&context);
+            });
+
+            let global = self.global();
+            global
+                .as_window()
+                .task_manager()
+                .dom_manipulation_task_source()
+                .queue(task, global.upcast())
+                .unwrap();
+        }
+
+        match pname {
+            constants::QUERY_RESULT => Ok(self.query_result.get()),
+            constants::QUERY_RESULT_AVAILABLE => Ok(self.query_result_available.get().unwrap()),
+            _ => unreachable!(),
+        }
+    }
+}
+
+impl Drop for WebGLQuery {
+    fn drop(&mut self) {
+        self.delete(true);
+    }
+}