Event Pipelines

[TomAtkinsonArm]

Description

Builds on-top of #485.

The Event Bus allows for communication between components and the firing of one off events. It does not allow for a Sample to continually fire and react to a given sequence of events.

Pipelines aim to allow stages to continually run without the need for an Event Observer to submit the event manually. This allows a sample to have a very compact view of its execution flow. Samples can now have completely different execution flows.

Example

// hello world

struct Context{
    // ... Global Vulkan Handles
};

struct FrameContext {
    // ... per frame Vulkan handles
};

class FrameManager : public EventObserver {
    // ... React to window updates, recreate the Swapchain, recreate frame data
};

std::shared_ptr<ExitOnEscape> exit_on_escape() {
    // ... default exit behaviour defined some where else in the project
    static std::shared_ptr<ExitOnEscape> observer = std::make_shared<ExitOnEscape>();
    return observer;
}

// ... project defined update stage
struct UpdateEvent {
    float delta_time;
};

class Update : public TypedPipelineStage<UpdateEvent>;

// ... project defined draw stage
struct DrawEvent {
    CommandPool& pool;
};

class Draw : public TypedPipelineStage<DrawEvent>;

void sample_main(void* platform_context) {
    auto window = windows::_default(platform_context, "Hello Triangle");

    Context context{};

    // ... init Vulkan stuff

    auto frame_manager = std::make_shared<FrameManager>(context);
    
    EventPipeline pipeline;

    pipeline
      .attach(window)
      .attach(frame_manager)
      .attach(exit_on_escape())
      .then(std::make_shared<Update>())
      .then(std::make_shared<Draw>());

    // ... step pipeline
    while(true) {
        // process will eventually have error handling
        // its likely that this statement will be
        // return pipeline.run();
        // where run() internally has a loop and return on error or close
        pipeline.process(); 
    }
}

[SaschaWillems]

Technically this looks great, but I'm not sure if we want to use the term pipeline for this. I fear that people could get confused with having graphics pipelines and also pipelines for event related stuff?

[TomAtkinsonArm]

Technically this looks great, but I'm not sure if we want to use the term pipeline for this. I fear that people could get confused with having graphics pipelines and also pipelines for event related stuff?

@SaschaWillems EventPipeline?

[TomAtkinsonArm]

Rebased on events_bus

[SaschaWillems]

Yes, I'm fine with EventPipeline. That's a clear distinction between this and Vulkan's pipeline. The PR looks fine to me, but just as with the event bus PR I can't seem to find or run the tests for this in VS2019.

[TomAtkinsonArm]

The PR looks fine to me, but just as with the event bus PR I can't seem to find or run the tests for this in VS2019.

Try ctest --output-on-failure --test-dir=<build/folder> also configure using -DVKB_BUILD_TESTS=ON

[SaschaWillems]

Tried running that, but it just tells me that no tests were found. Even when building with -DVKB_BUILD_TESTS=ON. Maybe we can take a look at this in today's call.

[TomAtkinsonArm]

In the CI we use:

cmake -H"." -B"build/windows" -DVKB_BUILD_TESTS=ON
cmake --build "build/windows" --target vkb_tests --config Debug --parallel
ctest --output-on-failure --test-dir "build/windows" -C Debug

This also works locally for me

[TomAtkinsonArm]

Rebased @SaschaWillems @asuessenbach is this ready to be approved?

[TomAtkinsonArm]

Comments resolved, merging for now. The concept will evolve over time and more than likely be replaced in the near future if it does not fit its desired use case.