2.7 KiB
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Command-handlers are classes that implement the WingHandler interface. The command's json parameters automatically get injected into the handler's properties using reflection code. Check out a few handlers to see how this works.
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Class WingFetcher can precisely and easily retrieve objects of all different kinds using a 'path'. Study the API of this class, we use it everywhere. It is the best tool when you need the caller to specify a blueprint, or a graph, or a pin - you name it.
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When you want to scan for a list of assets, MCPAssets is the best tool. This wraps Unreal's asset database in a convenient interface. Please study this API.
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The only valid way to get a name for an object is using WingUtils::FormatName(obj). We don't allow the use of pin->GetName, or node->GetTitle, or any other name-fetching routine. Using only WingUtils::FormatName guarantees consistency: that means, names output by one tool can be parsed by a different tool.
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To check whether a string matches an object's name, there's only one valid way to do that as well: using bool WingUtils::Identifies(Name, Obj).
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Concise output is better. The output of these handlers will primarily be consumed by LLMs with finite context windows. Avoid sending information the caller didn't ask for. Don't echo the command parameters: the caller knows what parameters he sent. Don't make things unnecessarily verbose: "type=int varname=x" can be shortened to "int x." Generate output in a form that you would want to consume.
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You can pass the output StringBuilder directly into WingFetcher and MCPAssets. If you do, these will automatically generate good error messages. If either of these classes returns 'false', you don't need to generate an error message: it's already been done. Any other routine that accepts MCPErrorCallback can do the same.
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It's good for handlers to do operations in batches, where possible. SpawnNodes is better than SpawnNode. When an LLM calls into an MCP, it often takes 15 to 30 seconds. It's important that ConnectPins can do batches, because building a graph can involve connecting dozens of pins.
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It is traditional to use UE_LOG in unreal code, but it really doesn't work for us: you see, the LLM invoking the MCP can't see the log messages, so what's the point? Better to report problems via the response. Please remove UE_LOG calls in handlers.
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When you're going to edit something, it's important to mark things dirty. There's a very powerful tool for that: WingUtils::PreEdit and WingUtils::PostEdit, which can also be accessed through WingFetcher::PreEdit and PostEdit. These routines are very careful about marking everything dirty, so you don't have to worry about it.