is Skija mandatory requirement for JWM?

[chirontt]

The README says:

JWM/README.md

Line 22 in d5fe7cb

- Plays well with (but does not require) [Skija](https://github.com/HumbleUI/Skija)

But even an example as simple as the empty example requires Skija:

JWM/examples/empty/java/Example.java

Line 19 in d5fe7cb

window.setLayer(new LayerGLSkija());

and its input loop need it too:

JWM/examples/empty/java/Example.java

Lines 53 to 54 in d5fe7cb

	} else if (e instanceof EventFrameSkija ee) {
	Surface s = ee.getSurface();

The above ee.getSurface() call returns a Skija surface instance, which makes Skija a mandatory requirement for JWM. But is it an absolute requirement?

Here's my use-case: if I have a Skia surface (note: not Skija surface) acquired by my own FFM utility to Skia, which is just a pointer to a sk_surface_t instance, how can I attach (or link) this Skia surface to a JWM window/panel to display its contents on screen (and without Skija requirement)?

[dzaima]

See https://github.com/HumbleUI/JWM/blob/main/shared/java/skija/LayerGLSkija.java (or the other layer types); those are also responsible of making the EventFrameSkija events happen.

You can make a similar custom LayerGL implementation (+ making a new event type, or just directly running your code in the frame() function), fully avoiding io.github.humbleui.skija.

The built-in one is just there for convenience, you can choose to not use it even when using Skija.

[tonsky]

What @dzaima said is correct. Skija layers are there for convenience, but are not a requirement. As long as you don’t use these classes Skija is not required on classpath.

To answer your question, you basically need to implement Layer interface: attach, resize, reconfigure, frame etc. JWM will call those when it’s time to render or when surface needs to resize. After that it’s all up to you.

Unfortunately we don’t have a good example to demonstrate a completely custom layer, but it would be cool to have. Meanwhile you can look at our Skija layer implementations to understand how to integrate sk_surface_t

[chirontt]

Thanks for all the info. I will try studying the LayerRasterSkija class first, for raster-based surface, before trying the LayerGLSkija one for GL surface.

For GL, I will need to initialize the GL context first and make it active for the current thread; Skia doesn't do this by itself.

Looking at the LayerGLSkija code, I notice this method call:

JWM/shared/java/skija/LayerGLSkija.java

Line 24 in d5fe7cb

makeCurrent();

which is calling the native method _nMakeCurrent() in its parent class LayerGL. Can I assume that JWM does the GL context initialization in this native method?

[tonsky]

yes, sources are in corresponding folders (macos, linux etc) https://github.com/HumbleUI/JWM/blob/d5fe7cb75892280b58fd39c93374fe81a1326939/macos/cc/LayerGL.mm

[chirontt]

Hmmm, the Mac native code does implement it:

JWM/macos/cc/LayerGL.mm

Lines 131 to 135 in d5fe7cb

	extern "C" JNIEXPORT void JNICALL Java_io_github_humbleui_jwm_LayerGL__1nMakeCurrent
	(JNIEnv* env, jobject obj) {
	jwm::LayerGL* instance = reinterpret_cast<jwm::LayerGL*>(jwm::classes::Native::fromJava(env, obj));
	[instance->fGLContext makeCurrentContext];
	}

But the corresponding Windows native code is a NO-OP:

JWM/windows/cc/LayerWGL.cc

Lines 246 to 248 in d5fe7cb

	extern "C" JNIEXPORT void JNICALL Java_io_github_humbleui_jwm_LayerGL__1nMakeCurrent
	(JNIEnv* env, jobject obj) {
	}

and so is the Linux native code:

JWM/linux/cc/LayerGL.cc

Lines 109 to 111 in d5fe7cb

	extern "C" JNIEXPORT void JNICALL Java_io_github_humbleui_jwm_LayerGL__1nMakeCurrent
	(JNIEnv* env, jobject obj) {
	}

or am I looking at the wrong native code for them?

[dzaima]

Not an expert on how GL works, but that should be the correct spot for LayerGL::_nMakeCurrent; JWM does have a suspicious this on its frame dispatch, that bypasses the java function's emptiness:

JWM/linux/cc/WindowManagerX11.cc

Lines 295 to 298 in d5fe7cb

	if (p->_layer) {
	p->_layer->makeCurrent();
	}
	p->dispatch(classes::EventFrame::kInstance);

[chirontt]

I see, thanks. And similarly, here's the relevant code for Windows:

JWM/windows/cc/LayerWGL.cc

Lines 109 to 114 in d5fe7cb

	// Listen to window events
	_callbackID = _windowWin32->addEventListener([this](WindowWin32::Event event){
	switch (event) {
	case WindowWin32::Event::SwitchContext:
	makeCurrent();
	break;

Not sure how the WindowWin32::Event::SwitchContext event should be sent (automatically? or triggered by what code? and where?)

I'm testing it in Windows, and I can confirm that there's no automatic GL context initialization by JWM, thus resulting in failure in my code to create a GL native interface for Skia (i.e. via the gr_glinterface_create_native_interface() native call).

[tonsky]

Sorry, I am not familiar with that code. Maybe try doing what our implementation does?