[External] : Re: JavaFX Direct3D 12 rendering pipeline for Windows

[Lukasz Kostyra]

Hi Nir,

Thanks for suggestions! Apologies for being a bit late, needed to wrap my head around FFM before responding.

In many cases I mostly followed D3D9 backend's design, so the similarities can be there. =) But there definitely is room for improvement which I also see and would like to tackle before the backend reaches a "mature enough" state. When working on 3D part of JFX I also saw that there is some data duplication happening, especially with Light/Mesh/MeshView code. I'd like to trim this as well, but it was not a priority yet - I preferred to have a working code now and all sorts of cleanups or reorganizations like that can come later.

Regarding FFM - that is an interesting idea that we could explore at some point, but I'm not sure if we could (or even should) move all the implementation details to Java and limit native calls to just D3D12. There are a few problems with that:
  - There is quite a bit of logic which integrates better on C/C++ side with D3D12, mostly due to 12's low-level-ness. Rewriting those in Java feels like quite a bit of a task in itself, and might create more problems than it solves.
  - Raising the abstraction from 12’s low-level approach instead of just making a “passthrough” is also something that’s quite frequently done, mostly to make the API a bit more useable and suitable for project’s specific needs (see ex. NativeBuffer abstractifying 12’s heap types into simply data being CPU visible, or code managing mid-frame data like CommandLists, shader constants, 2D vertices etc.). This could also help later down the line when adding potential new features, simplifying the calls made from Java side.
  - There might be some implications related to using jextract on third-party headers that we are unsure of and would require additional approvals before proceeding with this specific approach.

The most reasonable/probable FFM use would be to access a D3D12 backend DLL we create (so basically accessing current prism_d3d12.dll but with FFM and not JNI). But it is something that we can explore in the future, for now I think there are more higher-priority tasks related to this backend.

Lukasz

From: Nir Lisker <nlisker at gmail.com>
Sent: Tuesday, 15 October 2024 14:28
To: Lukasz Kostyra <lukasz.kostyra at oracle.com>
Cc: openjfx-dev <openjfx-dev at openjdk.org>
Subject: [External] : Re: JavaFX Direct3D 12 rendering pipeline for Windows

This is exciting news!

I looked at the code quickly. Here are my thoughts.

My biggest remark is that JNI is still being used, which is being more and more restricted. Recently, Kevin announced that we will be FFM-ready, surely by the time this pipeline is released. I would like to see (and can help, having used FFM since incubation) D3D12 being based on FFM.

This will also allow less cluttered code to be written with less effort. Consider this mess in D3D12NativeMeshView (exists in D3D9 also, not blaming you for this :) ):

    private native void nSetLight(long ptr, int index, float x, float y, float z, float r, float g, float b,
                                  float enabled, float ca, float la, float qa, float isAttenuated, float maxRange,
                                  float dirX, float dirY, float dirZ, float innerAngle, float outerAngle, float falloff);

That, in a pure Java world, would be `void nSetLight(Light)` with `Light` holding all its parameters. In fact, this could make whole files that just prepare the data for the native layer redundant. At least I know this is the case in the current D3D9 implementation.

It might also be the case that the pointer juggling that we do currently (using `long ptr` everywhere) will not be needed because FFM does it for us (Arena takes care of the lifecycle context). However, when it comes to resource deallocation there are many caveats, so I'm speculating here.

Another design element that I think we can get rid of is the duplication of data structures in the Java and native sides. if Java has a Light, Material, and Mesh, the native side doesn't need them in reality, but in D3D9 (and somewhat in D3D12) it does have them. Without checking, I suspect that this duplication leads to inefficient memory usage. I speculate that it was done to minimize the number of native calls, a consideration that could be overturned with FFM. In general, a lot of the code in C++ can be potentially moved to Java, with only the calls to DirectX being left of course.

Thanks for this herculean effort!

On Mon, Oct 14, 2024 at 7:10 PM Lukasz Kostyra <lukasz.kostyra at oracle.com<mailto:lukasz.kostyra at oracle.com>> wrote:
Hello openjfx-dev,

we just pushed a prototype of a new JavaFX Direct3D 12 rendering pipeline
for Windows to a new "direct3d12" branch on jfx-sandbox. It is more than an
experiment branch - we intend to fully develop the D3D12 backend there.

We're not necessarily looking for contributions at this point, but if anyone
has early feedback about it or wants to try it by building it themselves,
that would be fine. We also did not test it on a wider range of hardware, so
your mileage may vary. While D3D12 pipeline will build by default, D3D9
pipeline is still the default pick at runtime. To run anything on D3D12
pipeline you need to force it with ex.:
  java -Dprism.order=d3d12 ...

Backend supports 2D rendering (albeit with some graphical issues here and there
that need to be ironed out) and basic 3D rendering. Expect not everything fully
working yet (ex. some gradients on 2D controls are incorrect, or 3D-in-2D will
straight up not work) and the performance not matching D3D9 yet. Our goal is to
first reach feature completion and then focus on performance.

Lukasz
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