New frame control functionality examples

[p...@ciklum.com]

Hi!

I am wondering whether there are some examples or use cases (on NodeJS) on how to use HeadlessExperimental.beginFrame and Target in order to control screenshots rate? Because from the documentation it is not really clear how to use them. 

[p...@ciklum.com]

If to be concrete currently we initialize Target:
 

 let logLine = '[NodeJS: Connecting to chrome...]';
        request.post('http://127.0.0.1:40000/videoCapture/log/'+ jobId, {json: logLine});
        client = await CDP('ws://localhost:9222/devtools/browser');

        const {Target} = client;
        const {browserContextId} = await Target.createBrowserContext();

        const {targetId} = await Target.createTarget({
            url: url,
            width: viewportWidth,
            height: viewportHeight,
            enableBeginFrameControl: true
        });

        client = await CDP({target: targetId});
/* ... */
 await Emulation.setDeviceMetricsOverride(deviceMetrics);
        await Emulation.setVisibleSize({
            width: viewportWidth,
            height: viewportHeight
        });

await Page.navigate({url});
await Page.loadEventFired();

  await HeadlessExperimental.enable();
        await HeadlessExperimental.needsBeginFramesChanged();

and the script halts on needsBeginFramesChanged event.

[Eric Seckler]

There's a doc about the concepts behind it on https://bit.ly/headless-rendering. Apart from that, I'd recommend looking at the test cases here: 

https://cs.chromium.org/chromium/src/headless/lib/headless_web_contents_browsertest.cc?l=447

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[Eric Seckler]

In particular, the beginFrame command requires a few additional command line flags (see the doc / tests) and only works in --headless mode.

[p...@ciklum.com]

Yes, we have also used all additional recommended flags for starting chrome from the "Rendering in Headless Chrome" doc:

--enable-surface-synchronization

   --run-all-compositor-stages-before-draw

   --disable-threaded-animation

   --disable-threaded-scrolling

   --disable-checker-imaging

When we are not setting enableBeginFrameControl: true page is loaded and we can see it rendered in debug, but if the flag is set then page doesn't load, maybe we are not firing some event?


[Eric Seckler]

Only thing I can think of is that you're somehow missing the initial HeadlessExperimental.needsBeginFramesChanged event. It may be sent before the Headless.enable command completes. Try setting an async event handler for it before sending Headless.enable?

To view this discussion on the web visit https://groups.google.com/a/chromium.org/d/msgid/headless-dev/9e8d0afa-1673-4152-b46c-bdcdc92f8a56%40chromium.org.