PlatformEventSink.h

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#pragma once
 
// A module's hook into the raw platform event stream.
//
// The SDL pump used to translate every event itself, which meant it had to know
// about keyboard, joystick, touch, window, graphics, audio and ui -- eight
// upward dependencies from what should be one of the lowest modules, and the
// last dependency cycle in the engine.
//
// Now each module registers a sink for the events it owns. The pump drains the
// platform queue and offers each event to the sinks in priority order; whoever
// recognises it translates it. Modules the build does not contain simply have
// no sink, so the pump keeps working with any subset linked in.
//
// Providers depend on event (downwards, which is fine); event depends on none
// of them.
//
// `nativeEvent` is the backend's own event object -- SDL_Event* for the SDL
// backend. Only sinks built against the active backend are ever registered, so
// the cast is safe; the sinks in question are themselves backend code
// (keyboard/sdl, touch/sdl, ...).
 
#include "common/Capability.h"
#include "common/Export.h"
 
namespace eve::event {
 
class Message;
 
class EVENGINE_API IPlatformEventSink {
public:
    enum Priority {
        kObserver = 0,    // sees everything before anyone claims it (UI)
        kSurface = 10,    // window / swapchain lifecycle
        kInput = 20,      // keyboard, joystick, touch
    };
 
    static constexpr const char* capabilityName = "eve.event.IPlatformEventSink";
    virtual ~IPlatformEventSink() = default;
 
    virtual bool observePlatformEvent(const void* nativeEvent) { return false; }
 
    virtual Message* translatePlatformEvent(const void* nativeEvent) { return nullptr; }
 
    virtual void onPumpFinished() {}
};
 
}  // namespace eve::event