Game Editing > 3D Modeling & Content Creation

[Unreal][U1] Exporting .T3D files from Blender to Unreal

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kat:
Basically BSP (Binary Space Partitioning) is an optimised game world based on volume, i.e. three-dimensional areas defined by a set of boundary coordinates. For Unreal BSP is 'negative' in that volumes are carved from the world, whereas idTech is 'positive', volumes are placed into a void. Both create blocks and areas. Models on the other hand are 'skins', they're essentially a collection of linked 2D plains manipulated into a shape resembling something.

A Cube for example as a model, has 8 corner vertices that are able to describe 6 plains / 2D faces (three of which will share one vertex at a corner) that just happen to form a closed mesh. As a volume, those same verts and faces define a volume, an areas bound by those elements. The difference largely boils down to this: a mesh can have openings and gaps, a volume can't, they always have to be solid (if they are not they're no longer volumes).

And this is basically where the problem lies, in converting models to brush volumes, each 2D face has to be given 'depth' or 'volume' to be meaningful in BSP world space. The extrusions that occur to facilitate that are where errors tend crop up (notwithstanding grid and other issues already mentioned). This means if you're making something specifically for converting to brushes you ideally need to structure the model so its made from blocks and volumes.

Asaeis Wi Vio:

--- Quote from: kat on March 15, 2016, 09:54:04 AM ---Basically BSP (Binary Space Partitioning) is an optimised game world based on volume, i.e. three-dimensional areas defined by a set of boundary coordinates. For Unreal BSP is 'negative' in that volumes are carved from the world, whereas idTech is 'positive', volumes are placed into a void. Both create blocks and areas. Models on the other hand are 'skins', they're essentially a collection of linked 2D plains manipulated into a shape resembling something.

A Cube for example as a model, has 8 corner vertices that are able to describe 6 plains / 2D faces (three of which will share one vertex at a corner) that just happen to form a closed mesh. As a volume, those same verts and faces define a volume, an areas bound by those elements. The difference largely boils down to this: a mesh can have openings and gaps, a volume can't, they always have to be solid (if they are not they're no longer volumes).

And this is basically where the problem lies, in converting models to brush volumes, each 2D face has to be given 'depth' or 'volume' to be meaningful in BSP world space. The extrusions that occur to facilitate that are where errors tend crop up (notwithstanding grid and other issues already mentioned). This means if you're making something specifically for converting to brushes you ideally need to structure the model so its made from blocks and volumes.

--- End quote ---

Ah, when you said volume model and mesh skins I thought you were refferring to something else. In Unreal 'brushes' have the capacity to be much more complicated fluid than such as in the idtech engines. The brush/model i have going here is sealed, by BSP holes I was refferring to the phenomenon occurable within the Unreal engine, where sometimes the nodes on surfaces don't get compiled properly, end up leaving a hole through geometry, a HOM, or a kind of 'non-space' (when, where touched things instantly get killed or get deleted if they have the property to collide with the world).

Unreal has the capacity to have both subtractive space, subtractive brushes, additive space or additive brushes, (negative and additive BSP brushes/negative and additive BSP voids as you mentioned) rather than strictly one :P

The example shown as a brush(s) in the last picture are actually not healthy for the way Unreals' BSP system works, in a sense that if you were to make something complicated with bare primitives it would cause more strain for the compiling process and more geometric instability, so after construction it's often customary to make 'large objects' into single brushes so that the game engine potentially handles them better (if the author puts them together relatively right).

So, BSP holes are sortof the downside to being able to have much more complicated and larger maps, sadly.

So that being said, there's probably some other issue causing the BSP holes, one can be as you said where vertecies do not go on the proper grid co-ordinates, but other things can trigger this too, just that apart from the grid problem (which I have adjusted in blender) there has to be something causing the geometric instability, just wish I knew what however.

kat:
You'll need to do a bit of experimenting using some simpler structures... it may just be the relative complexity of the mesh being converted that's causing the problem. If that's the case it may be a better option to split the model into sections in Blender and then essentially stitch it back together in UnrealEd once the parts are loaded.

Asaeis Wi Vio:
Thanks for the help, I'll try to see what I can do with splitting the model up. Can't touch the middle section too much as I have a cave in there :P

Either way, when the subsequent 227 update is released, it might clean up the BSP compiling system to better optimize the geometry, hopefully it should be improved enough to fix some issues (hopefully).

Asaeis Wi Vio:
Hey again Kat,

After some experimenting with exporting world geometry to UnrealEd from Blender, I noticed that the suggested grid spacing of Scale: 8 and Subdivisions: 8, doesn't actually match up with the lowest grid spacing of Ued, this could be why I've been having various problems with the BSP, after some fiddling (and meticulously counting grid spaces in the Ued orthagonal view/Blender orthagonal view), I have discovered that the actual setting for blender should be Scale: 16 and Subdivisions: 4. I thought of mentioning this here so that anybody else looking for the answer of how to properly set up an Unreal style grid in Blender could find it.

If you have any Unreal engine 1 relevant tutorials about importing world geometry from Blender, it might be worth updating the Scale: 8 and Subdivisions: 8 configuration to the configuration mentioned above. :P

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