Re: How are events passed between chrome and content?

[Jim Porter]

On 6/16/17 6:18 AM, smaug wrote:
> On 06/16/2017 02:32 AM, Jim Porter wrote:
>> Here's the code I'm currently using to generate a contextmenu event:
>> .
>>
> That just dispatches the event to dom. No forwarding to child process
> will happen.
> You need to use methods in nsIDOMWindowUtils to dispatch events in a way
> which simulates real events better
> and causes forwarding to happen.

Awesome, it works! Thanks for the pointer.

Now I just need to work on making this into a WebExtension... :)

- Jim
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Re: How are events passed between chrome and content?

[smaug]

On 06/16/2017 02:32 AM, Jim Porter wrote:

On 6/15/17 4:12 PM, Kartikaya Gupta wrote:

Not quite. For e10s, mouse events are sent across the process boundary
using the PBrowser ipdl protocol. On the parent side they go into
EventStateManager::DispatchCrossProcessEvent [1] which picks up the
TabParent and sends it over IPC to the TabChild. The TabChild then
dispatches it to the PuppetWidget in the content process.


Thanks for the code reference! That at least gives me a rough idea of
where all this is happening so I can maybe debug it.


If you set the right flags on the event it should get through.
Presumably you're creating this event from JS - you want to make sure
that it creates a WidgetMouseEvent with eContextMenu message type. I
don't know if that can be done without using the DOMWindowUtils APIs.
Posting your code snippet for event creation might help.


Here's the code I'm currently using to generate a contextmenu event:
.

That just dispatches the event to dom. No forwarding to child process will 
happen.
You need to use methods in nsIDOMWindowUtils to dispatch events in a way which 
simulates real events better
and causes forwarding to happen.



As mentioned, it works fine for creating a context menu in chrome, but
not content. (It also works fine in non-e10s content, but that shouldn't
be surprising.) I might be missing something, but when I looked in the
inspector, I didn't see any obvious differences between this event and
the original contextmenu event that I suppressed.

Maybe there's some issue with the event target? When the original
contextmenu event is fired, it says the target is the XUL tabbrowser
(#content) and the originalTarget is the XUL browser element. I've tried
dispatching my synthetic event to both, but neither does anything.

I've also tried keeping the original contextmenu event around that I
suppressed and re-dispatching that, but it doesn't work either. However,
since I called .preventDefault()/.stopPropagation() on that object, I'm
not sure I'd expect it to work anyway.

- Jim



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Re: How are events passed between chrome and content?

[Jim Porter]

On 6/15/17 4:12 PM, Kartikaya Gupta wrote:
> Not quite. For e10s, mouse events are sent across the process boundary
> using the PBrowser ipdl protocol. On the parent side they go into
> EventStateManager::DispatchCrossProcessEvent [1] which picks up the
> TabParent and sends it over IPC to the TabChild. The TabChild then
> dispatches it to the PuppetWidget in the content process.

Thanks for the code reference! That at least gives me a rough idea of
where all this is happening so I can maybe debug it.

> If you set the right flags on the event it should get through.
> Presumably you're creating this event from JS - you want to make sure
> that it creates a WidgetMouseEvent with eContextMenu message type. I
> don't know if that can be done without using the DOMWindowUtils APIs.
> Posting your code snippet for event creation might help.

Here's the code I'm currently using to generate a contextmenu event:
.
As mentioned, it works fine for creating a context menu in chrome, but
not content. (It also works fine in non-e10s content, but that shouldn't
be surprising.) I might be missing something, but when I looked in the
inspector, I didn't see any obvious differences between this event and
the original contextmenu event that I suppressed.

Maybe there's some issue with the event target? When the original
contextmenu event is fired, it says the target is the XUL tabbrowser
(#content) and the originalTarget is the XUL browser element. I've tried
dispatching my synthetic event to both, but neither does anything.

I've also tried keeping the original contextmenu event around that I
suppressed and re-dispatching that, but it doesn't work either. However,
since I called .preventDefault()/.stopPropagation() on that object, I'm
not sure I'd expect it to work anyway.

- Jim
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Re: How are events passed between chrome and content?

[Kartikaya Gupta]

On Thu, Jun 15, 2017 at 4:16 PM, Jim Porter  wrote:
> From what I can tell, if I click inside a webpage, the event starts out
> in chrome and then propagates down into content. I assume there's some
> sort of magic happening in the message manager that pushes the event
> across process boundaries.

Not quite. For e10s, mouse events are sent across the process boundary
using the PBrowser ipdl protocol. On the parent side they go into
EventStateManager::DispatchCrossProcessEvent [1] which picks up the
TabParent and sends it over IPC to the TabChild. The TabChild then
dispatches it to the PuppetWidget in the content process.

> I'm working on a Firefox add-on for mouse gestures and as part of this I
> need to delay the opening of the context menu on Linux to occur on
> mouseup rather than mousedown. I do this by swallowing the original
> contextmenu event with .preventDefault()/.stopPropagation(). Then on
> mouseup, I synthesize my own contextmenu event. This works fine when
> clicking on something in chrome, but no context menu pops up if I click
> on something in content.

If you set the right flags on the event it should get through.
Presumably you're creating this event from JS - you want to make sure
that it creates a WidgetMouseEvent with eContextMenu message type. I
don't know if that can be done without using the DOMWindowUtils APIs.
Posting your code snippet for event creation might help.

[1] 
http://searchfox.org/mozilla-central/rev/20d16dadd336e0c6b97e3e19dc4ff907744b5734/dom/events/EventStateManager.cpp#1228
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How are events passed between chrome and content?

[Jim Porter]

>From what I can tell, if I click inside a webpage, the event starts out
in chrome and then propagates down into content. I assume there's some
sort of magic happening in the message manager that pushes the event
across process boundaries. However, I can't figure out how to create my
own event in chrome and have it propagate down into content. Is there
any code/documentation I should be looking at to figure out how to do this?

If you're wondering why I want to know about this, read on; otherwise,
you can stop here.

I'm working on a Firefox add-on for mouse gestures and as part of this I
need to delay the opening of the context menu on Linux to occur on
mouseup rather than mousedown. I do this by swallowing the original
contextmenu event with .preventDefault()/.stopPropagation(). Then on
mouseup, I synthesize my own contextmenu event. This works fine when
clicking on something in chrome, but no context menu pops up if I click
on something in content.

- Jim
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