servo/components/canvas/webgl_mode/inprocess.rs

/* 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::gl_context::GLContextFactory;
use crate::webgl_thread::{TexturesMap, WebGLMainThread, WebGLThread, WebGLThreadInit};
use canvas_traits::webgl::webgl_channel;
use canvas_traits::webgl::DOMToTextureCommand;
use canvas_traits::webgl::{WebGLChan, WebGLContextId, WebGLMsg, WebGLPipeline, WebGLReceiver};
use canvas_traits::webgl::{WebGLSender, WebVRRenderHandler};
use embedder_traits::EventLoopWaker;
use euclid::default::Size2D;
use fnv::FnvHashMap;
use gleam::gl;
use servo_config::pref;
use std::cell::RefCell;
use std::collections::HashMap;
use std::default::Default;
use std::rc::Rc;
use std::sync::{Arc, Mutex};
use webrender_traits::{WebrenderExternalImageApi, WebrenderExternalImageRegistry};

/// WebGL Threading API entry point that lives in the constellation.
pub struct WebGLThreads(WebGLSender<WebGLMsg>);

pub enum ThreadMode {
    MainThread(Box<dyn EventLoopWaker>),
    OffThread(Rc<dyn gl::Gl>),
}

impl WebGLThreads {
    /// Creates a new WebGLThreads object
    pub fn new(
        gl_factory: GLContextFactory,
        webrender_api_sender: webrender_api::RenderApiSender,
        webvr_compositor: Option<Box<dyn WebVRRenderHandler>>,
        external_images: Arc<Mutex<WebrenderExternalImageRegistry>>,
        mode: ThreadMode,
    ) -> (
        WebGLThreads,
        Option<WebGLMainThread>,
        Box<dyn WebrenderExternalImageApi>,
        Option<Box<dyn webrender::OutputImageHandler>>,
    ) {
        let (sender, receiver) = webgl_channel::<WebGLMsg>().unwrap();
        // This implementation creates a single `WebGLThread` for all the pipelines.
        let init = WebGLThreadInit {
            gl_factory,
            webrender_api_sender,
            webvr_compositor,
            external_images,
            sender: sender.clone(),
            receiver,
        };

        let output_handler = if pref!(dom.webgl.dom_to_texture.enabled) {
            Some(Box::new(match mode {
                ThreadMode::MainThread(..) => OutputHandler::new_main_thread(),
                ThreadMode::OffThread(ref webrender_gl) => {
                    OutputHandler::new_off_thread(webrender_gl.clone(), sender.clone())
                },
            }))
        } else {
            None
        };

        let (external, webgl_thread) = match mode {
            ThreadMode::MainThread(event_loop_waker) => {
                let textures = Rc::new(RefCell::new(HashMap::new()));
                let thread_data =
                    WebGLThread::run_on_current_thread(init, event_loop_waker, textures.clone());
                (
                    WebGLExternalImages::new_main_thread(textures),
                    Some(thread_data),
                )
            },

            ThreadMode::OffThread(webrender_gl) => {
                WebGLThread::run_on_own_thread(init);
                (
                    WebGLExternalImages::new_off_thread(webrender_gl, sender.clone()),
                    None,
                )
            },
        };

        (
            WebGLThreads(sender),
            webgl_thread,
            Box::new(external),
            output_handler.map(|b| b as Box<_>),
        )
    }

    /// Gets the WebGLThread handle for each script pipeline.
    pub fn pipeline(&self) -> WebGLPipeline {
        // This mode creates a single thread, so the existing WebGLChan is just cloned.
        WebGLPipeline(WebGLChan(self.0.clone()))
    }

    /// Sends a exit message to close the WebGLThreads and release all WebGLContexts.
    pub fn exit(&self) -> Result<(), &'static str> {
        self.0
            .send(WebGLMsg::Exit)
            .map_err(|_| "Failed to send Exit message")
    }
}

/// Bridge between the webrender::ExternalImage callbacks and the WebGLThreads.
enum WebGLExternalImages {
    OffThread {
        webrender_gl: Rc<dyn gl::Gl>,
        webgl_channel: WebGLSender<WebGLMsg>,
        // Used to avoid creating a new channel on each received WebRender request.
        lock_channel: (
            WebGLSender<(u32, Size2D<i32>, usize)>,
            WebGLReceiver<(u32, Size2D<i32>, usize)>,
        ),
    },
    MainThread {
        textures: TexturesMap,
    },
}

impl WebGLExternalImages {
    fn new_off_thread(webrender_gl: Rc<dyn gl::Gl>, channel: WebGLSender<WebGLMsg>) -> Self {
        WebGLExternalImages::OffThread {
            webrender_gl,
            webgl_channel: channel,
            lock_channel: webgl_channel().unwrap(),
        }
    }

    fn new_main_thread(textures: TexturesMap) -> Self {
        WebGLExternalImages::MainThread { textures }
    }
}

impl WebrenderExternalImageApi for WebGLExternalImages {
    fn lock(&mut self, id: u64) -> (u32, Size2D<i32>) {
        match *self {
            WebGLExternalImages::OffThread {
                ref webgl_channel,
                ref webrender_gl,
                ref lock_channel,
            } => {
                // WebGL Thread has it's own GL command queue that we need to synchronize with the WR GL command queue.
                // The WebGLMsg::Lock message inserts a fence in the WebGL command queue.
                webgl_channel
                    .send(WebGLMsg::Lock(
                        WebGLContextId(id as usize),
                        lock_channel.0.clone(),
                    ))
                    .unwrap();
                let (image_id, size, gl_sync) = lock_channel.1.recv().unwrap();
                // The next glWaitSync call is run on the WR thread and it's used to synchronize the two
                // flows of OpenGL commands in order to avoid WR using a semi-ready WebGL texture.
                // glWaitSync doesn't block WR thread, it affects only internal OpenGL subsystem.
                webrender_gl.wait_sync(gl_sync as gl::GLsync, 0, gl::TIMEOUT_IGNORED);
                (image_id, size)
            },

            WebGLExternalImages::MainThread { ref textures } => {
                let textures = textures.borrow();
                let entry = textures
                    .get(&WebGLContextId(id as usize))
                    .expect("no texture entry???");
                (entry.0, entry.1)
            },
        }
    }

    fn unlock(&mut self, id: u64) {
        match *self {
            WebGLExternalImages::OffThread {
                ref webgl_channel, ..
            } => {
                webgl_channel
                    .send(WebGLMsg::Unlock(WebGLContextId(id as usize)))
                    .unwrap();
            },

            WebGLExternalImages::MainThread { .. } => {},
        }
    }
}

/// struct used to implement DOMToTexture feature and webrender::OutputImageHandler trait.
type OutputHandlerData = Option<(u32, Size2D<i32>)>;
enum OutputHandler {
    OffThread {
        webrender_gl: Rc<dyn gl::Gl>,
        webgl_channel: WebGLSender<WebGLMsg>,
        // Used to avoid creating a new channel on each received WebRender request.
        lock_channel: (
            WebGLSender<OutputHandlerData>,
            WebGLReceiver<OutputHandlerData>,
        ),
        sync_objects: FnvHashMap<webrender_api::PipelineId, gl::GLsync>,
    },
    MainThread,
}

impl OutputHandler {
    fn new_off_thread(webrender_gl: Rc<dyn gl::Gl>, channel: WebGLSender<WebGLMsg>) -> Self {
        OutputHandler::OffThread {
            webrender_gl,
            webgl_channel: channel,
            lock_channel: webgl_channel().unwrap(),
            sync_objects: Default::default(),
        }
    }

    fn new_main_thread() -> Self {
        OutputHandler::MainThread
    }
}

/// Bridge between the WR frame outputs and WebGL to implement DOMToTexture synchronization.
impl webrender::OutputImageHandler for OutputHandler {
    fn lock(
        &mut self,
        id: webrender_api::PipelineId,
    ) -> Option<(u32, webrender_api::units::FramebufferIntSize)> {
        match *self {
            OutputHandler::OffThread {
                ref webrender_gl,
                ref lock_channel,
                ref webgl_channel,
                ..
            } => {
                // Insert a fence in the WR command queue
                let gl_sync = webrender_gl.fence_sync(gl::SYNC_GPU_COMMANDS_COMPLETE, 0);
                // The lock command adds a WaitSync call on the WebGL command flow.
                let command =
                    DOMToTextureCommand::Lock(id, gl_sync as usize, lock_channel.0.clone());
                webgl_channel
                    .send(WebGLMsg::DOMToTextureCommand(command))
                    .unwrap();
                lock_channel.1.recv().unwrap().map(|(tex_id, size)| {
                    (
                        tex_id,
                        webrender_api::units::FramebufferIntSize::new(size.width, size.height),
                    )
                })
            },

            OutputHandler::MainThread => unimplemented!(),
        }
    }

    fn unlock(&mut self, id: webrender_api::PipelineId) {
        match *self {
            OutputHandler::OffThread {
                ref webrender_gl,
                ref mut sync_objects,
                ..
            } => {
                if let Some(gl_sync) = sync_objects.remove(&id) {
                    // Flush the Sync object into the GPU's command queue to guarantee that it it's signaled.
                    webrender_gl.flush();
                    // Mark the sync object for deletion.
                    webrender_gl.delete_sync(gl_sync);
                }
            },

            OutputHandler::MainThread => {},
        }
    }
}