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Invalid Clipping
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 Re: Invalid Clipping
Posted by Stadric on Sat Jan 13th at 6:22am 2007

I have a valid brush, I clip it, I clip it again, I clip it a third time, and eventually, for some unknown reason, it has become unable to be clipped again, because that will make it invalid.
That sounds feasible to me, but I'm unable to justify it in my mind. I can't figure out how clipping a valid brush can create an invalid brush.
Can you?

I'll admit that this doesn't look topic worthy, but this question has been bothering me for a while. I'm sure someone has a diagram or something, I just can't picture it in my mind right now.


Also change the texture of the dock. Docks are rarely tile. -Facepunch
As I Lay Dying



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 Re: Invalid Clipping
Posted by Crono on Sat Jan 13th at 7:00am 2007

It's happened to me plenty of times, but in the cases I've done it, the brush was valid it just clipped it in funky ways (not pertaining to the plane I gave it, for example). I've really avoided the clip tool a lot because I've found that it just screws stuff up very often. More than likely, unless it's incredibly complex, I'll just vertex manipulate the brush.

But that's just personal preference. But, I do know what you're talking about.


Blame it on Microsoft, God does.



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 Re: Invalid Clipping
Posted by Captain P on Sat Jan 13th at 11:18am 2007

I might've stumbled upon this a few times, but I can't remember them. Then again, I usually clip 'clean', e.g. using a rough grid-size. I don't use a lot of complex brushes usually, but when I do, I use a combination of the clip and vertex tool.


Create-ivity - a game development blog



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 Re: Invalid Clipping
Posted by Orpheus on Sat Jan 13th at 11:36am 2007

Its happened to me a few times, but I tend to build at 90* angles so clipping an invalid direction is rare.

The stairs I originally built for PitCrew had an invalid solid caused by clipping.

The stairs originally went up but at a 45* angle, The steps were not horizontal and I clipped them to match the upwardness. Actually they were horizontal, but only if you turned toward them and looked up.

God thats hard to explain, but the point is, even though every clip was precise, one of them borked during a compile. Borked so badly, that the error when deleted, moved on to the next step. I had to delete the entire stairway to correct the error.

I doubt many remember the steps but they were better than the current ones by far. However Dietz took umbrage to them, since I borrowed them from a Quake map. I removed them for the harmony of the maps authors.

But yes, it can happen. My advice, if you want to create one, make multiple cuts on multiple solids, one of them will bork out eventually. Doing so with only one solid kinda makes the eventuality infinitely small.





The best things in life, aren't things.



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 Re: Invalid Clipping
Posted by reaper47 on Sat Jan 13th at 4:19pm 2007

I don't remember this happening to me (although I doubt it didn't) but clipping can create ugly out-of-grid geometry depending where the cutting-points are placed.

If you cut a brush at a very odd angle, with the two points out of the brush's borders you can create two new corners that are out of grid. If you cut them again, Hammer could decide to help you by slightly snapping the vertices to the grid (or a maybe a grid smaller than 1) which might snap them in the wrong direction. That way the brush could become concave by 1 Unit or less.

I think it's a grid problem.


Why snark works.



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 Re: Invalid Clipping
Posted by Stadric on Sat Jan 13th at 8:39pm 2007

That seems feasible, reaper.


Also change the texture of the dock. Docks are rarely tile. -Facepunch
As I Lay Dying



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 Re: Invalid Clipping
Posted by Captain P on Sat Jan 13th at 8:56pm 2007

I don't think it's a grid snapping problem - that would only surface when compiling - but probably a floating point precision problem. With vertices off the grid, you could get locations like 510.00562028 and the like. Since this precision isn't perfect (and the higher the value before the point, the less precision behind it) it could, in some circumstances, results in a slightly curved surface.

Just a theory, but hey. <img src=" SRC="images/smiles/icon_smile.gif">


Create-ivity - a game development blog




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