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Data-Only Blueprints/Subclassing Blueprints

Can blueprints be subclassed? I can understand some the technical difficulties of overriding functions in new blueprints, however if it's to be a replacement for unrealscript, it must?

I found documentation for data-only blueprints here, which would fit my needs perfectly, but I can't figure out how to create one. I've tried right-clicking on my Blueprint and selecting "Create Blueprint based on this" but I always get an "Invalid class with which to make a Blueprint" message.

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asked Mar 11 '14 at 03:54 AM in Everything Else

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ue4-archive ♦♦ STAFF
50k 3670 1999 9124

avatar image ue4-archive ♦♦ STAFF Mar 11 '14 at 03:54 AM

Hi Tom, not sure if this is an answer, but what i have tried is to create a new blueprint then search the class tree to find the base that i want and choose that. I think that they show as data only till you add something to the Script section

but right clicking on the blueprint and then extend from when seem to be the most logical way of doing it

avatar image ue4-archive ♦♦ STAFF Mar 11 '14 at 03:54 AM

George, I've tried doing that but my Blueprint doesn't show up in the class tree (none of my custom blueprints do, only the base classes).

Edit: I see now. When i create a blueprint from a Script based class it's IsDataOnly variable is True (an example is the Blueprint'/Engine/EngineDamageTypes/DmgTypeBP_Environmental.DmgTypeBP_Environmental' blueprint)

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Hey Thomas,

Data only blueprints sound like they might be a great solution for you. As of right now by default you can not derive one blueprint from another but you can enable this feature if you wish. Simply close the editor, go to Engine/Config/BaseEngine.ini and change this below to true, save and reopen the editor.

[Kismet]
AllowDerivedBlueprints=false

Let us know if this works for you.

Best Regards, Ryan Van Enkevort

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answered Mar 11 '14 at 03:54 AM

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ue4-archive ♦♦ STAFF
50k 3670 1999 9124

avatar image ue4-archive ♦♦ STAFF Mar 11 '14 at 03:54 AM

This is correct! For a little background, the reason we haven't flipped the switch yet is because we want to get the UI for inherited components a little tighter before allowing people to go all out with creating derived components. As soon as that's in, we'll flip the switch for everyone.

avatar image ue4-archive ♦♦ STAFF Mar 11 '14 at 03:54 AM

Hey, that kinda worked. I can now easily create a blueprint from my existing blueprint. I'm assuming I'm looking at something that's got a ways to go, but the only variables I can modify in my derived blueprint's defaults are bools (Missing are the arrays and floats). Will these eventually be supported? Is there an alternative method I should use to access and modify the values? (note: i can access the variables in the node graphs, etc. just not in the Defaults)

avatar image ue4-archive ♦♦ STAFF Mar 11 '14 at 03:54 AM

There shouldn't be any restrictions on the variables you can edit in a derived class. Whether or not you can edit it should only depend on if the variable is exposed (i.e. the "Editable" checkbox is checked in the variable properties). If you see the highlighted eye icon next to the variable name, you should see it in the properties of the derived class.

avatar image ue4-archive ♦♦ STAFF Mar 11 '14 at 03:54 AM

Oh! I see it now. That's an interesting design choice. I don't immediately see the advantage, other than less clutter. My issue with it is that I don't want to expose those variables to the LD, as there will never be a need to change them in the level and they could make things break.

avatar image ue4-archive ♦♦ STAFF Mar 11 '14 at 03:54 AM

Eventually, the plan will be to make variables have three modes of exposure: private (editable only on the defining blueprint), protected (editable only on the defining blueprint and its children), and public (editable on blueprints, and any instances). That should give the granularity that you need, but unfortunately, in the meantime, it's just a binary exposure.

avatar image ue4-archive ♦♦ STAFF Mar 11 '14 at 03:54 AM

Thanks for the insight. I know, I'm poking around in unfinished business, so i appreciate the support, but now I can keep going with my fancy parking-lot-maker Blueprint! :D

avatar image ue4-archive ♦♦ STAFF Mar 11 '14 at 03:54 AM

No problem! Sorry for the inconvenience, and thanks for all your patience as we keep on building :)

avatar image ue4-archive ♦♦ STAFF Mar 11 '14 at 03:54 AM

This was actually incredible helpful, as I was looking to do this exact thing. Thank you!

avatar image ue4-archive ♦♦ STAFF Mar 11 '14 at 03:54 AM

The next beta should have full support for derived blueprints turned on by default, but in the current beta that's out there, you have to enable blueprints based on other blueprints in your engine INI file:

[Kismet] AllowDerivedBlueprints=true

avatar image ue4-archive ♦♦ STAFF Mar 11 '14 at 03:54 AM

Which Engine ini is that exactly? The DefaultEngine.ini in Project/Config/ or Project/Saved/Config/Windows that keeps getting reset?

Edit: Oh nevermind, I have it in the right ini and its not working.

avatar image ue4-archive ♦♦ STAFF Mar 11 '14 at 03:54 AM +

Engine/Config/BaseEngine.ini

avatar image BenjvC Jan 02 '16 at 08:37 PM +

Hello Ryan,

Searching "nested Blueprints" I came upon this thread, see it's not exactly apples for apples with my case, seems this addresses data BPs, which I'm unfamiliar with. If I may share my situation and ask a question. I had hired a developer to build two BPs, one for a character player and the other for a lighting prop with a flickering candlelight behavior.

The player picks up the candle, which then stays locked to the camera as user navigates a cave. I opened the FirstPersonCharacter BP and noted how everything was organized, another light source prop of a flashlight parented to Camera. I replace this flashlight with the candle prop by a) dragging the candle BP into the Components tab parenting under FirstPersonCamera. I positioned the mesh w/ point light in the Viewport, compiled and entered play mode to test.

The point light was where I expected it to be and lit the scene, but as I navigated back I noted the mesh/point light was left behind, so first question is how to rectify this issue. One thing I noticed when dragging in this candle light BP is that a parent/child icon displayed next to it, did so regardless of which level in the Component tab I dropped it into. I read your advice above about editing the BaseEngine.ini changing 'AllowDerivedBlueprints=False' to true, and when I went to do this I noticed it was already set to true, which I half expected in light of your adding the bit about soon flipping the switch as the default.

There's a bit more to it here, b) the flickering behavior of the candle light. My developer pointed me to the nodes within the Event Graph pertaining to this flickering effect, suggested I open candle BP, copy/paste that group of nodes into an empty space of the Event Graph within the FirstPersonCharacter BP. Nada. We're guessing, so enough with that ;^)

Thanks for some ideas how I might make this work, appreciate your time.

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