53 lines
2.6 KiB
Markdown
53 lines
2.6 KiB
Markdown
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# Error Handling in Blueprints
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## Format Log Message Node
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We have implemented "Format Message", which is an improved version of Unreal's
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"Format Text". Unlike "Format Text", it has built-in support to print
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vectors, rotations, enums, and quite a few other types.
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We have also implemented "Format Log Message", which is like Format Message
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except that the output goes to the unreal logs. It might help to familiarize
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yourself with Unreal's built-in logging function, UE_LOG. Format Log Message
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is meant to be the Blueprint front end to UE_LOG.
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Format Message and Format Log Message both require a format string, which
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will typically look something like this:
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"Hello, {Name}, the weather today will be {Weather}"
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When you set a format string such as the one above, the Format Message node
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will add pins for the placeholders - in the example above, the pins
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Name and Weather would be added. These are wildcard pins that you can
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connect any printable value to.
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To make a new type printable, look at FormatDataLibrary.h
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Format Log Message accepts a severity level, this is directly based on
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the severity levels supported by UE_LOG. It adds *ThrottledDisplay* and
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*ThrottledLog*, which do the same thing as *Display* and *Log*, except
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that output is limited to one message per second.
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## The Blueprint Debugger Pauses on Error Messages
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The blueprint debugger will pause whenever you log an error message. This is functionality we have added to Unreal.
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You can control the severity at which it pauses: in the GameMode, there is a dropdown for the severity level.
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You can also effectively turn it off by telling to only pause on fatal errors.
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There is a quirk: the debugger pauses before the error gets put into the logs. So when you're in the
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blueprint debugger,
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the only place the error will appear is in the lower-right corner of the screen, where debugger messages are
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reported. You won't see the error in the unreal output log. If you single-step, the error will appear
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in the output log as well.
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To understand how this is implemented, it helps to understand that log messages in unreal go to a bunch of
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different output devices: the unreal editor output window, the visual studio output window, a log file, and
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several more places. To dispatch messages to all these different destinations, Unreal has an output device
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list that you can add an output device to.
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To implement this break-on-error-message functionality, we implemented a pseudo-output-device.
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The pseudo device doesn't actually send
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the error message anywhere, it just triggers the debugger. For more information about implementation,
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see BreakToDebugger.h
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