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Author Topic: Halo Weather Polyhedron Tutorial By DSalimander (with love) (14 messages, Page 1 of 1)
Moderators: Dennis

bingo
Joined: Sep 17, 2017


Posted: Nov 16, 2017 10:59 PM    Msg. 1 of 14       
Be advised that a lot of terminology used in this tutorial is aimed at people who have an already in-depth knowledge of the Halo 1 BSP creation process.

Weather polyhedra are used by Halo to define volumes in a BSP where weather particles such as snow, rain, and swamp bugs cannot spawn. This technique is frequently used in the Halo 1 campaign where you transition from interior sections to outside sections with weather. Without weather polyhedra, going from an interior cluster to an exterior cluster with weather would cause the weather to just instantly appear, which isn't realistic.

There is little explanation offered as to how these work. Tool offers no failure/success information when you attempt to implement them. And the icing on the cake: you can't even view these in Sapien like you can with portals. The only evidence to go off of is the information Guerilla offers on some of the single player BSPs in question, and a really unhelpful description offered by the HEK tutorial.


Going by what the HEK tutorial says, you could assume these work in a similar fashion to occlusion portals; but, Guerilla gives a few extra hints that we aren't simply dealing with flat polygons- we are dealing with actual 3D volumes. It's unclear exactly what is accepted by Halo as a polyhedron; the definition of a polyhedron is a solid figure with many plane faces, typically more than six. (Source: Google) After reviewing the average amount of planes per weather polyhedron in the campaign maps, I've drawn the conclusion that these must be simple primitives such as cubes. I've experimented with using more complex volumes and experienced a lot of failures. If needed, the simple cube volumes can intersect to form larger, more complex volumes.

To make your own weather polyhedra, you must add a material to your BSP model (in 3DS Max) called +weatherpoly. Assign this material to your sealed simple volumes, export and compile the BSP, then open the level in Sapien. These volumes are intended to encapsulate halls and rooms and therefore will intersect BSP geometry, which is perfectly normal. Understand that you must apply weather effects to clusters that may normally not have them, so they appear outside a window or doorway, as you stand within a weather polyhedron. The only clusters that will not receive the weather particle cluster information are clusters that have no line of sight to the exterior. Just keep these two facts in mind:
1. Weather particles will spawn everywhere, if you're in a cluster that has them enabled. However...
2. Weather particles will not spawn inside weather polyhedra.

Here is a demonstration of weather polyhedra in 3ds Max on a port of Halo 2 Lockout. The level needs to have nice transitions between indoor areas and outdoor areas with snow.

Here are the weather polyhedra that need to be implemented to keep snow out of the indoor areas. As you can see, some intersect each other, and some aren't perfect cubes. These have been tested and work fine.

This is what the scene looks like as it's ready to be exported.

A common problem you may encounter relates to weather particles seemingly phasing through walls in areas where they shouldn't be. There are a few things to consider like the size of the weather particles, how strong the wind is, etc. Those are possible sources of problems, but the easiest solution is to simply enlarge the weather polyhedra sizes. The example above isn't exactly the intended use of weather polyhedra, I suspect. I believe they're mainly intended to be used at transition points in a linear level where there are long hallways that open up to exterior areas. In those situations, theres no chance of particles bleeding through walls since you can enlarge the weather polyhedron as big as you want outside the sealed BSP.

One last thing of note, if you want to be a nice guy and include weather polyhedra in your map even though you don't intend to use any weather particle systems, that's very helpful for anybody who wants to mod your map and add weather particle systems in the future.

This tutorial is available in PDF here: https://www.pdf-archive.com/2017/11/17/halo-weather-poly-tutorial/. It will be rehosted here and a few other places eventually.

Edit- Fixed the formatting.
Edited by bingo on Nov 17, 2017 at 12:15 AM


Spiral
Joined: Apr 3, 2011

I hope i'm out of the way


Posted: Nov 16, 2017 11:12 PM    Msg. 2 of 14       
About time someone explained this. Makes it much easier to follow than having to guess and read a decade old post/tutorial.


Nickster5000
Joined: Dec 11, 2010

Sector 09 RR: 2017


Posted: Nov 16, 2017 11:23 PM    Msg. 3 of 14       
:two-thumbs-up:

awesome tutorial man.


Spartan314
Joined: Aug 21, 2010

Former biped rigger & FP animator


Posted: Nov 17, 2017 02:09 AM    Msg. 4 of 14       
Won't be able to use this but was certainly a nice read


Lateksi
Joined: Jan 1, 2010


Posted: Nov 17, 2017 03:26 AM    Msg. 5 of 14       
Thanks sali now I can finally make map set in a freezer!


bingo
Joined: Sep 17, 2017


Posted: Nov 17, 2017 06:20 AM    Msg. 6 of 14       
Quote: --- Original message by: Spiral
About time someone explained this. Makes it much easier to follow than having to guess and read a decade old post/tutorial.

I read a bunch of theories that weather polies work just like portals, and that is completely false. I legitimately think that nobody in the history of Halo CE has ever figured this out.


MosesofEgypt
Joined: Apr 3, 2013


Posted: Nov 17, 2017 11:06 AM    Msg. 7 of 14       
Interesting. From looking at the tag it appears that each polyhedra is defined by a sphere which the polyhedra planes jut off of based on their plane vector's angle and distance from center. From looking at it, it appears that they can be more complex than boxes, but unless I have some proof I'm not going to guarantee this.

EDIT: After taking a good look at it I believe the way it stores the polyhedra is by fitting a sphere around each one, and calculating planes that make up each face.

This is actually pretty efficient since they can could use this to quickly check if a point is definitely NOT inside the polyhedra, meaning a particle CAN spawn(just check if the distance from the point to the sphere's center is greater than the radius). If it IS inside the sphere, they just need to test if the point is behind each of the planes inside the polyhedra.

I'm not 100% certain, but this SHOULD mean that weather polyhedra MUST be convex objects. According to guerilla they can have up to 16 coplaner faces, just as long as the object is convex.

Edited by MosesofEgypt on Nov 17, 2017 at 04:23 PM
Edited by MosesofEgypt on Nov 17, 2017 at 11:57 PM


Bungie LLC
Joined: Dec 29, 2013

friendly neighborhood contrarian funposter


Posted: Nov 17, 2017 08:03 PM    Msg. 8 of 14       
I've been wondering about weather polyhedra forever, and had always assumed it had something to do with keeping weather particle effects from being obnoxious to interiors, but have never seen anything explaining how they work.

gud job :)


bingo
Joined: Sep 17, 2017


Posted: Nov 18, 2017 03:11 AM    Msg. 9 of 14       
Quote: --- Original message by: MosesofEgypt
I'm not 100% certain, but this SHOULD mean that weather polyhedra MUST be convex objects. According to guerilla they can have up to 16 coplaner faces, just as long as the object is convex.
http://www.differencebetween.info/sites/default/files/images/4/Convex_and_concave.jpg

This makes sense and agrees with the tests I performed.

Quote: --- Original message by: Bungie LLC
gud job :)

<3

Edit- Ew Moses did you stick HTML code into your post? Trying to quote you was a train wreck.
Edited by bingo on Nov 18, 2017 at 03:13 AM


MosesofEgypt
Joined: Apr 3, 2013


Posted: Nov 18, 2017 09:22 AM    Msg. 10 of 14       
Nope, no html for me, just that bbcode for the image. Also, maybe try making a hexadecahedron and see if that works for occluding weather. Would certainly prove my theory and make your tutorial more complete.


XxPopeAK49xX
Joined: Jan 31, 2016

It's better being a jerk.


Posted: Nov 18, 2017 07:01 PM    Msg. 11 of 14       
Very cool explanation and examples. On the bottom of those lockout structures, could you extrude the cubes down so that it doesn't look like snow is being generated from the structure when it falls?


il Duce Primo
Joined: Apr 22, 2007

CMT Team Leader


Posted: Nov 18, 2017 09:06 PM    Msg. 12 of 14       
Yes, you can extrude those cubes down. You could also extrude them down and collapse it into a point creating a cone shape.


XxPopeAK49xX
Joined: Jan 31, 2016

It's better being a jerk.


Posted: Nov 19, 2017 06:11 PM    Msg. 13 of 14       
Quote: --- Original message by: il Duce Primo
Yes, you can extrude those cubes down. You could also extrude them down and collapse it into a point creating a cone shape.


Awesome to know that.


Corvette19
Joined: Feb 27, 2007


Posted: Nov 27, 2017 11:14 PM    Msg. 14 of 14       
Great information

 

 
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