draft: Port 'Screencast' demo to Vala

[BharatAtbrat]

The current code does not work, the GStreamer Pipeline is causing issues. There might be some problems with the implementation

Note - The Camera port also does not work because it uses Gst Pipeline.

Screengrab of the error :

2024-06-14.23-00-30.mp4

[BharatAtbrat]

@Diego-Ivan I'd appreciate a review :). I don't think I understand how the pipeline works correctly

[Diego-Ivan]

The current code does not work, the GStreamer Pipeline is causing issues. There might be some problems with the implementation

Note - The Camera port also does not work because it uses Gst Pipeline.

It needs to Gst.init needs to be called, passing null should be allowed (as it is done in both the JS and Python demos). Do you know if there is any workaround for this @lw64 ?

I'd appreciate a review :). I don't think I understand how the pipeline works correctly

I'm really not a GStreamer guy, but up to my understanding, this is how it works:

1. The portal asks Pipewire for a file descriptor, which is the place where it will write the camera frames so the app can read them.
2. The file descriptor will be given to the pipewiresrc element, which is the responsible to read the frames.
3. When the pipewiresrc reads one, it will push it to a queue which contains the frames that need to be drawn.
4. The glsinkbin will pop a frame from the queue and will "create the instructions" to draw it.
5. The gtk4paintablesink will receive the instructions and will draw the frame to a Gtk.Picture

[BharatAtbrat]

The current code does not work, the GStreamer Pipeline is causing issues. There might be some problems with the implementation
Note - The Camera port also does not work because it uses Gst Pipeline.

It needs to Gst.init needs to be called, passing null should be allowed (as it is done in both the JS and Python demos). Do you know if there is any workaround for this @lw64 ?

I'd appreciate a review :). I don't think I understand how the pipeline works correctly

I'm really not a GStreamer guy, but up to my understanding, this is how it works:

1. The portal asks Pipewire for a file descriptor, which is the place where it will write the camera frames so the app can read them.
2. The file descriptor will be given to the pipewiresrc element, which is the responsible to read the frames.
3. When the pipewiresrc reads one, it will push it to a queue which contains the frames that need to be drawn.
4. The glsinkbin will pop a frame from the queue and will "create the instructions" to draw it.
5. The gtk4paintablesink will receive the instructions and will draw the frame to a Gtk.Picture

I did try calling Gst.init() but it doesn't allow me to use null as a parameter, it instead requires a ref weak string[]?
Using ref args with arguments from the main method, the error goes away but the demo fails to start

[Diego-Ivan]

I did try calling Gst.init() but it doesn't allow me to use null as a parameter, it instead requires a ref weak string[]?
Using ref args with arguments from the main method, the error goes away but the demo fails to start

@BharatAtbrat I use this very ugly workaround to test it:

unowned string[] workaround = null;
Gst.init (ref workaround);

But I think this is an issue with the Vala bindings, it should allow null.

[sonnyp]

Is this still an issue with 47?

[Diego-Ivan]

Unfortunately yes, but I think we can use the workaround I suggested to have this merged. I don't think it would be a big deal.

Just tested the demo and it works perfectly, thank you so much @BharatAtbrat !

[lw64]

But I think this is an issue with the Vala bindings, it should allow null.

I don't think this second use of the function can be expressed in the Vala bindings, you probably would need to create a second binding for the function that executed it with null values. Maybe gst.init_null (), feel free to add it :)

[BharatAtbrat]

But I think this is an issue with the Vala bindings, it should allow null.

I don't think this second use of the function can be expressed in the Vala bindings, you probably would need to create a second binding for the function that executed it with null values. Maybe gst.init_null (), feel free to add it :)

Adding it directly brings up an error saying the name init_null does not exist. What am I doing wrong?

[lw64]

What do you mean with "adding directly"? I meant changing the vapi

[BharatAtbrat]

What do you mean with "adding directly"? I meant changing the vapi

Oh my bad :P, I thought this already existed