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GeezerVison is showing github.com — libprocessing ffi error handling by tychedelia · Pull Request #1293 · processing/processing4

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tychedelia commented Oct 16, 2025

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Sets up basic bevy App initialization and cross-FFI error handling.

Our strategy here is the following: Java should do any validation necessary before calling into the FFI layer. Errors are assumed to be unrecoverable and evidence of us doing something wrong. So we don't return error codes or anything but just check the error status as a string so we can at least throw a helpful exception for bug reports.

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          FFI error setup

b3d9d84

tychedelia requested a review from catilac

October 16, 2025 20:59


          Clear before init.

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catilac reviewed

Oct 16, 2025

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libProcessing/Cargo.toml Resolved

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catilac reviewed

Oct 16, 2025

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libProcessing/renderer/Cargo.toml

		tracing = "0.1"
		tracing-subscriber = "0.3"
		bevy = { version = "0.16", no-default-features = true, features = [
		"bevy_render"

catilac Oct 16, 2025

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for wayland windowing we need to add "wayland" to the features array

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catilac Oct 16, 2025

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if it's helpful, i can do it separately so i can actually test

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tychedelia Oct 16, 2025

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we'll def need more fleshing out here, i think there's a bunch of other stuff we'll want too. we're just generally going to be doing the "annoying" bevy integration version where we fine grain select what we want. this is to keep the final dylib small for packaging. see also the recently merged bevyengine/bevy#21472 which could be helpful for us.

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catilac Oct 17, 2025

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that looks cool. maybe useful for per-target customization

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catilac approved these changes

Oct 17, 2025

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Great! I like the error approach too. And if we ever for whatever reason needed to share more details then we can just serialize more information.

I'm approving, but also curious about what things will look like, say, if they write an erroneous compute shader.

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libProcessing/renderer/Cargo.toml

		tracing = "0.1"
		tracing-subscriber = "0.3"
		bevy = { version = "0.16", no-default-features = true, features = [
		"bevy_render"

catilac Oct 17, 2025

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that looks cool. maybe useful for per-target customization

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Stefterv reviewed

Oct 17, 2025

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core/src/processing/webgpu/PWebGPU.java

		*/
		public static long add(long left, long right) {
		return processing_h.processing_add(left, right);
		private static void checkError() {

Stefterv Oct 17, 2025

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So this means we would need to poll the rust side for any errors?

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tychedelia Oct 17, 2025

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yup, this is a tedious consequence of ffi code. there are a few different c-style error patterns you can use, but they're all pretty manual. rust exceptions (panics) can't cross the ffi boundary (doing so is undefined behavior).

realistically, we'll probably only end up having like 20ish ffi functions. if we had hundreds, i'd suggest writing an annotation processor or some other kind of reflection magic in java to automate this.

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Stefterv Oct 17, 2025

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Okay and there is no way from Rust to push an event into Java?

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tychedelia commented Oct 17, 2025

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I'm approving, but also curious about what things will look like, say, if they write an erroneous compute shader.

i think we'll def run into situations like this. what i'd propose is that we write a validate_shader ffi function that can eagerly check and return structured output. but also, there's nothing preventing us from returning a custom ffi error type for a given operation where it would be helpful, for example:

struct ValidationResult {
    error_code: u8,
    data: *const c_void,
}

in rust applications, you typically will bubble up Result using ? to a top level handler that will either log or panic. and so the pattern in this pr basically just ensure that we can reliably return results from our internal library code.

on the java side, we're using unchecked exceptions. right now it's just a general "something went wrong" exception class, but we could totally add an error code in addition to message and sub-type more on the java side if we do want to throw something like ValidationException.

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catilac merged commit 33b8b52 into processing:the-wgpu-moment

Oct 17, 2025

catilac added a commit that referenced this pull request

Jul 8, 2026


          Merge WebGPU backend (#1514)

25bca44

* *:ꔫ:*Renderer Project*:ꔫ:*

* Create workspaces for ffi and the renderer (#1275)

* Inital scaffold for libprocessing ffi.

* Remove EAP.

* Update docs.

* Factor out gradle utils. Add flag for disabling webgpu and enforcing android source level compat.

* Remove processing.h

* Set java version for all projects.

* libprocessing ffi error handling (#1293)

* FFI error setup

* Clear before init.

* Basic app lifecycle / surface creation.

* Throw when not on macos.

* Implement `background` method (#1308)

* Implement background.

* Install wayland deps.

* Support for windows surfaces. (#1310)

* Implement basic rendering flow (#1322)

* Implement basic rendering flow

* Fix naming.

* Actually fix rename.

* libprocessing submodule

* --recursive when cloning repo

* Enable submodule checkout in Gradle workflow

Added support for submodules in the checkout step.

* Enable submodules in checkout steps

Added submodule support to the checkout steps.

* Wayland support with new WebGPU renderer

* Gradle fixes from libprocessing refactor. (#1346)

* Updates from libprocessing. (#1392)

* Updates from libprocessing.

* Fixes for compat with main 17.

* Fixup docs.

* Upgrade to jdk-25.

* Upgrade to jdk-25.

* Materials, lights, input event forwarding, ellipse fix.

* Get the gradle sketch runner working locally.

* Conditionally execute webgpu tests

* ProcessingLibraryPlugin JVM Toggle update

* 4.5.5 in gradle.properties

* ProcessingPlugin fixes

---------

Co-authored-by: Moon D. <[email protected]>
Co-authored-by: Moon <[email protected]>
Co-authored-by: Stef Tervelde <[email protected]>

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catilac

catilac approved these changes

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Stefterv

Stefterv left review comments

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