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Let’s Talk About CEF

Dieses Thema im Forum "Developer News" wurde erstellt von Tyler Young, 12. April 2018.

  1. Tyler Young

    Gast

    In the X-Plane 11.20b1, we’re shipping a web browser for the first time. We’re using the Chromium Embedded Framework (CEF)—essentially the same guts as Chrome, wrapped inside X-Plane.

    For the time being, it’s being used in one place only*: to support in-app upgrades, so that if you have the demo, you can buy the full version of X-Plane without having to go to the web site. The web view is seamless—you can’t tell by looking at the app that it’s not just part of the native X-Plane user interface.

    While its present use is quite limited, if all goes well, we’d like to expand its use elsewhere in the sim—in The Glorious Future[​IMG], we could potentially use it to load online charts and the like.

    But, there’s a hitch!

    There’s not a good way to load two copies of CEF at a time. And, since some plugins (like the ones used in the new Flight Factor A320 Ultimate) depend on a version of CEF provided by a (global) plugin, we have to disable X-Plane’s web browser functionality in the presence of that plugin. This isn’t a big deal right now—after all, if you’ve installed payware, you probably already own the sim anyway—but it will be a shame if, in The Glorious Future[​IMG], you have to choose between your payware and core X-Plane functionality.

    The situation is even worse than you might expect: CEF absolutely doesn’t support multiple initialization calls in the lifetime of an app—you can’t initialize it, shut it down, then re-initialize it. That means it’s not even possible for plugin authors to be good citizens and “relinquish” CEF to X-Plane, such that you could at least use X-Plane’s browser whenever you’re not using an add-on that depends on it. It’s all or nothing! In fact, you’ll have to uninstall the CEF plugin before X-Plane can use a web view itself.

    There are two possible fixes here:

    1. At some point in the future, we provide access to CEF via the plugin SDK. If we did, it would have to be to the C API only—no fancy C++ wrappers for you. Speaking as someone with the memory of writing for the C API fresh in his mind, let me say: this isn’t a whole lot of fun, and it’s rife with the potential for memory leaks. Moreover, this would break any existing addons that depend on CEF—they would be forced to migrate to the SDK version of the API.
    2. We could (theoretically) compile an X-Plane-specific version of CEF that would not conflict with the version plugins are using. This would require renaming all the Objective-C symbols on Mac, and renaming the DLL on Windows. I’ve not investigated this for feasibility, but it’s certainly theoretically possible. This would allow X-Plane’s version of CEF to coexist with (one) plugin-provided copy, albeit at double the CPU and memory cost.

    Having us expose CEF via the SDK is not an unequivocal win. CEF is notoriously incompatible between versions—you can more or less guarantee that even minor updates will break compatibility of the API somewhere. That means X-Plane would be stuck at a fixed version of CEF for at least the lifetime of a major version to prevent breaking plugins. X-Plane 11.20 uses CEF release 3202; it would be at least the next major version before we updated CEF to a newer version. There are two major downsides to this:

    1. When X-Plane updates to that newer version, it would break plugins compiled against old versions of the SDK that depend on CEF. That’s a lot more aggressive than our normal deprecation policy, and it makes CEF plugins a potential maintenance headache for plugin devs.
    2. If your add-on really, really needs features from the latest and greatest CEF release, you’re out of luck—wait a couple years (!!) and maybe we’ll update.

    So, here’s what I’d like to hear from plugin devs:

    1. Are you currently, or are you planning to use CEF in the future?
    2. Would you be willing to use the C version of the CEF API only?
    3. Would you be able to accept the limitations and potential headaches (outlined above) of X-Plane-determined CEF versions and compatibility?

    If you don’t mind telling me a bit about your intended use cases, that’d be very helpful as well!

    EDITED TO ADD: There’s a third option here that I didn’t consider: X-Plane could provide a “wrapper” around CEF that offers “just” a browser surface, and simple interfaces like the ability to change the URL programmatically. This has the advantage that we could update CEF regularly without breaking the API (though there’s always the risk that a new version of Chromium would change how it handles your HTML + CSS + JS). The disadvantages are twofold:

    a) If a plugin developer really, really needs the full power of the CEF API, they’re out of luck (or we’re back to square one with respect to having to disable core X-Plane functionality in order to support the plugin).

    b) New XPLM APIs are a massive tax on our development time. Every time we need to make a change, we have to go test a dozen plugins… then go through an extensive beta… then inevitably hear about a show-stopping bug we introduced three hours after a release goes final. In contrast, providing a (major-version-stable), transparent copy of CEF costs us very little dev time; time that would otherwise be spent maintaining the XPLM API can be spent on, like, major features.

    * Aside: This is actually how we test a lot of new tech in X-Plane: we find a single, relatively out-of-the-way place to make use of it, ship it in a major version update, and wait to see if it blows up. Betas catch a lot of bugs, but not all, so this is a way of hedging our bets when it comes to code that hasn’t been battle-hardened. This is how we worked the bugs out of the user interface framework (Plane Maker’s panel editor was the testbed), the X-Plane 11 particle system (behind the scenes, it was used for some very minor effects in X-Plane 10.51), and more.

    The post Let’s Talk About CEF appeared first on X-Plane Developer.

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