Help with Generating code for Unreal Engine and GRPC [C++, MSVC 2017, Windows, master]

[fire]

Unreal engine has special macros for implementing instance method access.

How would I put this code generation in flat buffers and grpc?

Here is an example UE4 class.

//////////////////////////////////////////////////////////////////////////
// Base class for mobile units (soldiers)

#include "StrategyTypes.h"
#include "StrategyChar.generated.h"

UCLASS(Abstract)
class AStrategyChar : public ACharacter, public IStrategyTeamInterface
{
	GENERATED_UCLASS_BODY()

	/** How many resources this pawn is worth when it dies. */
	UPROPERTY(EditAnywhere, Category=Pawn)
	int32 ResourcesToGather;

	/** set attachment for weapon slot */
	UFUNCTION(BlueprintCallable, Category=Attachment)
	void SetWeaponAttachment(class UStrategyAttachment* Weapon);

	UFUNCTION(BlueprintCallable, Category=Attachment)
	bool IsWeaponAttached();

	protected:

	/** melee anim */
	UPROPERTY(EditDefaultsOnly, Category=Pawn)
	UAnimMontage* MeleeAnim;

	/** Armor attachment slot */
	UPROPERTY()
	UStrategyAttachment* ArmorSlot;

	/** team number */
	uint8 MyTeamNum;

	[more code omitted]
};

https://www.unrealengine.com/en-US/blog/unreal-property-system-reflection

Given the example greeter https://github.com/google/flatbuffers/blob/master/grpc/samples/greeter/greeter.fbs

It would probably look something like

DECLARE_DYNAMIC_MULTICAST_DELEGATE_OneParam( FHelloReplyDelegate, FHelloReply );


USTRUCT()
struct FHelloReply : public UObject
{
	GENERATED_UCLASS_BODY()
        UPROPERTY()
        UString message;
}

USTRUCT()
struct FHelloRequest : public UObject
{
	GENERATED_UCLASS_BODY()
        UPROPERTY()
        UString name;
}

USTRUCT()
struct FManyHellosRequest : public UObject
{
	GENERATED_UCLASS_BODY()
        UPROPERTY()
        UString name;
        UPROPERTY()
        uint8 num_greetings;
}

UCLASS()
class UGreeterBlueprintLibrary:
    public UBlueprintFunctionLibrary
{
    GENERATED_UCLASS_BODY()
    UFUNCTION(BlueprintCallable, Category="Greeter")
    static HelloReply SayHello(HelloRequest Hello);

    UFUNCTION(BlueprintCallable, Category="Greeter")
    // Requests the user to provide a callback  delegate
    // Returns 0 if Callback is not bound
    static int32 SayManyHellos(ManyHellosRequest Hello, FHelloReplyDelegate Callback); 
}

// Implement C++

Note that the coding standard for UE4 says that variables and functions should be PascalCased.

Edit #1: Changed from class to struct.
Edit #2: Added prefix to struct names.
Edit #3: Add delegate

[aardappel]

I'm not entirely sure what you're asking.

First, for the actual request/response messages, those will need to be in FlatBuffer format, so there is no automatic way to create those from a UObject / UProperties currently. You'll have to write code to construct a FlatBuffer from whatever is in your game objects explicitly.

For the client, there is no class structure requirement, you can put the code that creates a request wherever you want, including presumably inside these Unreal classes.

For the server, you need to inherit from the generated interface (in the sample case that is Greeter::Service, and implement the methods with the same interface. It may be possible to use multiple inheritance to add this directly to an Unreal class, but if not, you may be better of with a seperate server implementation that then calls into the apropriate Unreal classes afterwards.

[fire]

Sorry for not being clear. I want to generate a wrapper for

table HelloReply {
  message:string;
}

table HelloRequest {
  name:string;
}

table ManyHellosRequest {
  name:string;
  num_greetings:int;
}

rpc_service Greeter {
  SayHello(HelloRequest):HelloReply;
  SayManyHellos(ManyHellosRequest):HelloReply (streaming: "server");
}

and convert it to something like:

DECLARE_DYNAMIC_MULTICAST_DELEGATE_OneParam( FHelloReplyDelegate, FHelloReply );


USTRUCT()
struct FHelloReply : public UObject
{
	GENERATED_UCLASS_BODY()
        UPROPERTY()
        UString message;
}

USTRUCT()
struct FHelloRequest : public UObject
{
	GENERATED_UCLASS_BODY()
        UPROPERTY()
        UString name;
}

USTRUCT()
struct FManyHellosRequest : public UObject
{
	GENERATED_UCLASS_BODY()
        UPROPERTY()
        UString name;
        UPROPERTY()
        uint8 num_greetings;
}

UCLASS()
class UGreeterBlueprintLibrary:
    public UBlueprintFunctionLibrary
{
    GENERATED_UCLASS_BODY()
    UFUNCTION(BlueprintCallable, Category="Greeter")
    static HelloReply SayHello(HelloRequest Hello);

    UFUNCTION(BlueprintCallable, Category="Greeter")
    // Requests the user to provide a callback  delegate
    // Returns 0 if Callback is not bound
    static int32 SayManyHellos(ManyHellosRequest Hello, FHelloReplyDelegate Callback); 
}

// Implementation ...

This should be possible to do within the flatc executable.

[fire]

Where should I place this code to generate the wrappers?

[fire]

https://github.com/google/flatbuffers/blob/master/grpc/src/compiler/cpp_generator.cc is pretty ugly with its strings.

[aardappel]

That file is verbatim from the gRPC project.. to modify it, you'd make a PR with them first I guess. Not sure if they'd welcome an Unreal specific code generator.

What is ugly about it?

Instead you may want to just add an Unreal specific generator to FlatBuffers. Have a look to see how all the current generators work to get some inspiration for how to do that.

[stale]

This issue has been automatically marked as stale because it has not had activity for 1 year. It will be automatically closed if no further activity occurs. To keep it open, simply post a new comment. Maintainers will re-open on new activity. Thank you for your contributions.

[fire]

I've stopped using ue4.