treehouse/content/programming/unreal-engine.tree

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- this is that really cool game engine I work with on a daily basis

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    - so I have a lot of stuff to say about living with it, both good and not so good

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    - unfortunately most of those things I have to keep to myself because of NDA, but whatever is generally applicable I will put here

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+ ### Blueprint

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    - NOTE TO SELF: this section could really use some screenshots

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        - I don't have UE installed on my home computer yet, so you'll have to take my word for a lot of these things

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        - anyways back to your regularly scheduled bullet points, *\*ahem\**

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    + Blueprint, _my arch nemesis!_

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        - _WHAT! you don't remember me? how rude!_

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    - actually I really like Blueprint

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        + lots of visual languages generally feel really unpleasant to write (looking at you Scratch), but somehow Blueprint feels like exactly the opposite

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            - (it's possible Scratch got better since I last used it like 5 years ago but I remember it being pretty cumbersome to use.
              I had no reason to revisit it since so I simply don't know if it's any better now, but if it is, [let's chat][branch:hello]!)

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    - writing Blueprints is actually pretty darn nice and there's a lot to learn from the editor UX

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        - I say this mainly with regards to writing new nodes. it's as simple as dragging your mouse out of a pin, and a window will pop up giving you suggestions on what could be connected there

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        - then you select from the list and it creates the node, autoconnecting stuff as necessary

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            - one of the nicer autoconnections it can do is when you want to call a function on an actor component

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                - instance functions require you to pass in a `self` to call the function on

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                - so what it does is it suggests functions to call on all the _concrete components
                  you already have in your actor_, and when you select something like `Destroy Component (DefaultSceneRoot)`,
                  it'll not only create a function call node, but also hook up `DefaultSceneRoot` as its `self` parameter

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        - another cool thing that happens with nodes (or pins rather) is when you try to connect two pins of incompatible types

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            - Blueprint is strongly typed so you can't just pass in a `Float` where a `String` is expected

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            - but instead of having you explicitly type out "o dear Blueprint I would like to convert this `Float` to a `String`", you can just join the two pins together and it'll insert a
              conversion node for you automatically

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                - I do have a gripe with this though and it's where it places the node. it tries very hard to center it but unfortunately never succeeds. perhaps a bug I could fix one day?

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        - therefore most of the time writing Blueprints is very ergonomic

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            - except when it isn't because Blueprint is still an imperative language and has a concept similar to statements (`Exec` pins), which breaks the entire idea of pure data flow and
              introduces control flow into the mix

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                - this split is called _pure_ and _impure_ nodes, where impure nodes are those that perform control flow (ie. those with `Exec` pins)

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                - this results in weird edge cases like needing two separate node types to handle branching (one that can have side effects - `Branch`, and another that can't - `Select`)

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                    - `Branch` is used to shuttle control flow between two `Exec` lines, based on a `Bool`. you get a `True` branch and a `False` branch

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                    - and `Select` is used to choose a value based on another value, kind of like a ternary in C++

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                        - however it is quite annoying because you can only switch on enums (and other stuff that has a finite set of values,) whereas with `Branch` you can use any `Bool` condition you want

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                        - this would be fine if not for the existence of Gameplay Tags, which precisely _do not_ have a finite set of values

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                            - there is a `Switch on Gameplay Tag` node, but that is for control flow and not data flow!

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                            - this isn't an unsolvable problem but it illustrates the pure vs impure issue pretty well - you'd have to duplicate the implementation of `Switch on Gameplay Tag` to have
                              a version without an `Exec` pin

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                - in fact I'm seeing a bit of a semblance to the classic [function coloring problem][def:article/function_coloring]

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                    + except where it usually applies to the `async` concept found in most modern programming languages, here it applies to the concept of control flow vs data flow

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                        - and speaking of `async`, [Blueprint handles the classic `async` problem very gracefully][branch:01H8Y0CKD106HXQAJK87XV0H93]!

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        - did I mention how well Blueprints handle latent tasks?

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            - since control flow is based on those `Exec` pins, you can easily map your classic concept of callbacks to simply firing off the appropriate `Exec` pin

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            - for example the node for playing animations (`Play AnimMontage`) has a few pins coming out of it that signal playback events like `On Ended`, `On Blend Out`, `On Interrupted`

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                - and you wouldn't even know these are implemented as delegates in C++landia. it just feels like a first-class feature

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            - the only gripe I have is that you can only have latent nodes in the main event graph (you cannot have them within functions)

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                - which is annoying but not terrible, since most of that latent, high level gameplay logic happens inside the main event graph anyways

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    - maintaining Blueprints in a large project though could be a lot better

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        - with regards to your graphs becoming really large

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            - everybody kinda sorta just formats nodes however they see fit, and there is no unified autoformatter

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                - there's a reason people say Go's tooling is frickin' amazing, you know

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                + this results in what we Hat in Time modders used to call _Kismetti_ in the Unreal Engine 3 days but now we'd call _Blueprintti_

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                    + which is a portmanteau of Blueprint and spaghetti.

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                        - I can't believe I remembered the spelling of that word. *portmanteau*.

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        - with regards to assets (how long this darn stuff takes to load)

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            - the biggest offender here being that hard references are the default

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                - thus you can add a Mesh Component to your Blueprint and it'll load the entire thing when you wanna tweak a variable or some logic in the event graph

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                    - and not asynchronously in the background, you will have to _wait_ for it to finish loading. which is pretty annoying

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    - and the runtime performance isn't the best for a few reasons

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        - the VM isn't implemented in the most optimal way

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            - I've analyzed this in my [`dispatchers` repository][def:dispatchers/repo] if you wanna have a read

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        - and that hard reference thing can make gameplay stutter when you're loading in new assets, but that's a more widespread issue than just with Blueprints

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        - but in reality most of the logic you're implementing in Blueprints (high-level gameplay stuff) shouldn't be that performance sensitive

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            - and it's not hard to extract the performance sensitive parts to C++ because Blueprint offers tools for refactoring your code