Add a gstreamer servosrc plugin

Cargo.toml

@@ -1,6 +1,7 @@
 [workspace]
 members = [
     "ports/glutin",
+    "ports/gstplugin",
     "ports/libsimpleservo/capi/",
     "ports/libsimpleservo/jniapi/",
     "ports/libmlservo/",

etc/taskcluster/decision_task.py

@@ -207,6 +207,7 @@ def linux_tidy_unit():
             ./mach build --dev --features canvas2d-raqote
             ./mach build --dev --features layout-2020
             ./mach build --dev --libsimpleservo
+            ./mach build --dev -p servo-gst-plugin
             ./mach test-tidy --no-progress --self-test
 
             ./etc/memory_reports_over_time.py --test
@@ -485,6 +486,8 @@ def windows_unit(cached=True):
             "mach smoketest --angle",
             "mach package --dev",
             "mach build --dev --libsimpleservo",
+            "mach build --dev -p servo-gst-plugin",
+
         )
         .with_artifacts("repo/target/debug/msi/Servo.exe",
                         "repo/target/debug/msi/Servo.zip")

ports/gstplugin/Cargo.toml

@@ -0,0 +1,38 @@
+[package]
+name = "servo-gst-plugin"
+description = "A GStreamer plugin that provides servosrc"
+version = "0.0.1"
+authors = ["The Servo Project Developers"]
+license = "MPL-2.0"
+edition = "2018"
+build = "build.rs"
+repository = "https://github.com/servo/servo/"
+publish = false
+
+[lib]
+name = "gstservoplugin"
+crate-type = ["cdylib"]
+path = "lib.rs"
+
+[dependencies]
+crossbeam-channel = "0.3"
+euclid = "0.20"
+gleam = "0.6"
+glib = { version = "0.8", features = ["subclassing"] }
+gstreamer = { version = "0.14", features = ["subclassing"] }
+gstreamer-base = { version = "0.14", features = ["subclassing"] }
+gstreamer-gl = { version = "0.14", features = ["v1_16"] }
+gstreamer-video = { version = "0.14", features = ["subclassing"] }
+log = "0.4"
+lazy_static = "1.4"
+libservo = {path = "../../components/servo"}
+servo-media = {git = "https://github.com/servo/media"}
+sparkle = "0.1"
+# NOTE: the sm-angle-default feature only enables angle on windows, not other platforms!
+surfman = { version = "0.1", features = ["sm-angle-default", "sm-osmesa"] }
+surfman-chains-api = "0.2"
+surfman-chains = "0.2.1"
+
+[build-dependencies]
+gst-plugin-version-helper = "0.1"
+

ports/gstplugin/README.md

@@ -0,0 +1,131 @@
+# A GStreamer plugin which runs servo
+
+## Build
+
+```
+./mach build -r -p servo-gst-plugin
+```
+
+## Install
+
+By default, gstreamer's plugin finder will complain about any libraries it finds that aren't
+gstreamer plugins, so we need to have a directory just for plugins:
+```
+mkdir target/gstplugins
+```
+
+To install:
+```
+cp target/release/libgstservoplugin.* target/gstplugins
+```
+## Run
+
+To run locally:
+```
+GST_PLUGIN_PATH=target/gstplugins \
+  gst-launch-1.0 servosrc \
+    ! queue \
+    ! video/x-raw,framerate=25/1,width=512,height=512 \
+    ! videoflip video-direction=vert \
+    ! autovideosink
+```
+
+To stream over the network:
+```
+GST_PLUGIN_PATH=target/gstplugins \
+  gst-launch-1.0 servosrc \
+    ! queue \
+    ! video/x-raw,framerate=25/1,width=512,height=512 \
+    ! videoconvert \
+    ! videoflip video-direction=vert \
+    ! theoraenc \
+    ! oggmux \
+    ! tcpserversink host=127.0.0.1 port=8080
+```
+
+To  save to a file:
+```
+GST_PLUGIN_PATH=target/gstplugins \
+  gst-launch-1.0 servosrc num-buffers=2000 \
+    ! queue \
+    ! video/x-raw,framerate=25/1,width=512,height=512 \
+    ! videoconvert \
+    ! videoflip video-direction=vert \
+    ! theoraenc \
+    ! oggmux \
+    ! filesink location=test.ogg
+```
+
+*Note*: killing the gstreamer pipeline with control-C sometimes locks up macOS to the point
+of needing a power cycle. Killing the pipeline by closing the window seems to work.
+
+## Troubleshooting building the plugin
+
+You may need to make sure rust picks up the right gstreamer, for example:
+```
+PKG_CONFIG_PATH=$PWD/support/linux/gstreamer/gst/lib \
+LD_LIBRARY_PATH=$PWD/support/linux/gstreamer/gst/lib \
+  ./mach build -r -p servo-gst-plugin
+```
+
+## Troubleshooting running the plugin
+
+*Currently x11 support is broken!*
+
+First try:
+```
+GST_PLUGIN_PATH=target/gstplugins \
+  gst-inspect-1.0 servosrc
+```
+
+If that doesn't work, try:
+```
+GST_PLUGIN_PATH=target/gstplugins \
+  gst-in2spect-1.0 target/gstplugins/libgstservoplugin.so
+```
+
+If you get reports about the plugin being blacklisted, remove the (global!) gstreamer cache, e.g. under Linux:
+```
+rm -r ~/.cache/gstreamer-1.0
+```
+
+If you get complaints about not being able to find libraries, set `LD_LIBRARY_PATH`, e.g. to use Servo's Linux gstreamer:
+```
+LD_LIBRARY_PATH=$PWD/support/linux/gstreamer/gst/lib
+```
+
+If you get complaints `cannot allocate memory in static TLS block` this is caused by gstreamer initializing threads using
+the system alloc, which causes problems if those threads run Rust code that uses jemalloc. The fix is to preload the plugin:
+```
+LD_PRELOAD=$PWD/target/gstplugins/libgstservoplugin.so
+```
+
+You may need to set `GST_PLUGIN_SCANNER`, e.g. to use Servo's:
+```
+GST_PLUGIN_SCANNER=$PWD/support/linux/gstreamer/gst/libexec/gstreamer-1.0/gst-plugin-scanner
+```
+
+You may need to include other directories on the plugin search path, e.g. Servo's gstreamer:
+```
+GST_PLUGIN_PATH=$PWD/target/gstplugins/:$PWD/support/linux/gstreamer/gst/lib
+```
+
+Under X11 you may get complaints about X11 threads not being initialized:
+```
+GST_GL_XINITTHREADS=1
+```
+
+Under x11 you may get a frozen display from `autovideosink`, try `ximagesink` instead.
+
+Putting that all together:
+```
+GST_GL_XINITTHREADS=1 \
+GST_PLUGIN_PATH=$PWD/target/gstplugins/:$PWD/support/linux/gstreamer/gst/lib \
+GST_PLUGIN_SCANNER=$PWD/support/linux/gstreamer/gst/libexec/gstreamer-1.0/gst-plugin-scanner \
+LD_LIBRARY_PATH=$PWD/support/linux/gstreamer/gst/lib \
+LD_PRELOAD=$PWD/target/gstplugins/libgstservoplugin.so \
+  gst-launch-1.0 servosrc \
+    ! queue \
+    ! videoflip video-direction=vert \
+    ! ximagesink
+```

ports/gstplugin/build.rs

@@ -0,0 +1,7 @@
+/* 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/. */
+
+fn main() {
+    gst_plugin_version_helper::get_info()
+}