Maya 2012: Cutting up a polygon plane

[Anonymous]

Another problem I'm grapping with lately when creating a terrain is I don't want my entire terrain to be one enormous mesh - I want it to be broken up into smaller meshes so my renderer can skip portions of the terrain that are not in view.

As I see it there are two approaches I could take:

1. start with a large polygon plane and (after creating my heightmap) cut it into an array of smaller polygon planes.

2. build my terrain from smaller polygon planes to begin with, and combine them as "shells" into a single mesh. Then I can bulid my heightmap, then separate them again.

I am still doing a lot of googling and researching but tips and advice on this topic are much appreciated.

[Anonymous]

Well I attempted method 2. I created an array of polygon planes and tried to sculpt them. But even though they were combined, they came apart at the seems. 😕 Also, uploading an existing heightmap using the "Attribute map" section under the sculpt geometry tool appears to apply the heights to each shell individually, rather than the combined shells as a whole.

It looks like I'll have to go with 1. Cut the polygon plane into multiple meshes. Assuming these is any way to do this...  😕 It looks like there are easy ways to cut a polygon, but I haven't found any way of dividing up an entire mesh.

[damaggio]

Hi generalsolution, It would be easier to give you some advice if you could post some images of what you are trying to do as well as your ultimate goal with the project and the type of image, animation or game you intent to complete.

As I mentioned before there are other methods for dealing with large terrains but I cannot propose anything without knowing about the project.

[Anonymous]

Hi again, Damaggio!

A little background:

I am working on a rudimentary game-engine that I've coded almost entirely from scratch as a learning project and to support a unique game idea. I have written my own model loaders, graphics engine and shaders. I am currently using the Bullet physics engine for collision detection. I have been working on this on my spare time for a couple years now and things are going very well.

Rather than building a full blown level editor, I have been using certain naming and structure conventions in the FBX scene I build so the model loader knows what in game objects they represent. For example, if I have a mesh node called "pBox1_dynamic" my model loader understands that this is a dynamic box object, and it creates both graphics and collision information automatically. 

Current problem:

Right now, I am trying to modify my loader so that I can load height-maps into my game. The current structure I have planned for my Maya scene is:

1. Create 1 parent node named "heightMap_(some name)" 

2. Create 1 child node called "map" - this will store the heightmap texture in its material.

3. Create a child mesh node or node(s) that describe the terrain itself beneath the parent node.

What my loader will do:

1. Search for all nodes who's name begins with "heightMap" 

2. search its children for a "map" node. This will contain the heightmap texture. This will be passed to the Bullet physics engine to create the collision heightmap.

3. use the other child mesh node(s) to draw  the terrain itself, graphically.

This may sound like a lot of work but I only anticipate having one large heightmap per level. My approach for modeling the terrain will generally be:

1.start with an existing heightmap (probably one I created in photoshop) use the "attribute map" section of the sculpt

geometry tool to apply it to a polygon plane.

2. make some minor modifications to the terrain as I edit my-scene, probably with the sculpting tool.

3. generate a new heightmap for the new terrain (using the methods we discussed in my other thread) 

So up to now all that I have working, the problem is the size of the terrain.

My engine contains optimizations that avoid rendering meshes who's bounding boxes are outside of view for the current camera. For this reason, I would like to cut my final terrain into multiple mesh objects so that my game engine can avoid rendering large sections of the terrain that are not in view. See the picture below. Breaking up the mesh in this way can be done as a final step/optimization before exporting to FBX so I don't necessarily need to be able to sculpt the mesh after its broken up, but I do need to be able to partition it without modifying the texture mapping. I wouldn't want, for example, 4 copies of the blue circles to appear on each of the new meshes. If done right, the new 4 meshes would not be merely cut polygons or shells but distinct mesh nodes entirely.

Hope that makese sense, I know my purpose may be a bit obscure but I appreciate whatever ideas you have. If worse comes to worst I may need to just program my loader to break it up myself on load.

[damaggio]

Beautiful explanation  generalsolution...now is getting a little way over my head....I'm no game expert but why would your engine render or take in consideration something that is not in the camera  view yet?

Most engines artists would take the height map and generate their terrains there in the software and not import a mesh.

Now if you need to cut your terrain into 4 pieces you can either chop the height field in photoshop into 4 files and use it into 4 different poly meshes that way it would be cut already , by that I mean 4 separate planes side by side forming a larger square, then 4 shaders and the 4 cut height maps from photoshop, then use the Texture deformer in Maya, subdivide each poly planes to the resolution you want and control the height map with the texture deformer "strength"..

this can be found in Deform>Texture...or if you gonna be using the mesh instead then maybe you can slice the mesh with the Multicut tool or if the topology is clean with all quads you can select one quadrant and extract that part of the mesh then do the same for the other 3.

After that you can export each piece asn FBX.

Let me know if is not clear.

[Anonymous]

"why would your engine render or take in consideration something that is not in the camera  view yet?"

Exactly. It should not. However, determining exactly what polygons are in view before sending them down the rendering pipeline is an expensive and complicated process that may cost more time than it saves. Instead, it is usually much much faster to put the whole mesh into a bounding box and simply render all of its polygons if its bounding box is in view. i.e. trim off objects not in view on a per-mesh, instead of a per-polygon basis. It works well... provided the mesh (and therefore the bounding box) are not too big. In the case of my terrain, its bounding box will almost always be in view, so it will send every polygon down the pipeline. Most of them won't end up in view so it won't execute the pixel shader, but a lot of verticees would be processed.

Modifying my loader so that it can auto-generate my terrain from the heightmap is definitely do-able. I could include my own logic to split up the mesh that way. I was rather hoping to avoid that as it is a lot of work. I will weigh that in as a possible solution.

"maybe you can slice the mesh with the Multicut tool or if the topology is clean with all quads you can select one quadrant and extract that part of the mesh then do the same for the other 3."

That sounds like the only other possible route I'd take but Maya 2012 doesn't have multi-cut, it has the "split-polygon" tool which rather confounds me... haha. I've been trying to figure out how it works but have been struggling.

[damaggio]

I see, in that case then since you are in 2012 you could try selecting the faces and extracting into 4 pieces, I assume the original mesh is all quads when you sculpted so it should give you a straight line on the seams.

I believe in 2012 is under Edit Mesh >extract

Another way is making 4 copies of what you have, keep them on top of each other and then select the quadrant on  in each mesh you want to delete leaving them all in the same place.....now you have your four quadrants to export.

[Anonymous]

All good ideas! 

I do not have my maya machine with me but I will attempt it later. I am not familiar with "extract". Will it allow me to pull out a portion into an entirely new mesh, while preserving materials and texture coordinate info? 

[damaggio · Accepted solution]

Extract is under Mesh>Extract....the rest of the file should remain the same .

Here the plane mesh was divided 250x250 and extracted into 4 pieces.

[Anonymous]

That is awesome. Extract is just what I needed!

That brings me into the realm of having a working solution. I can, concievably, manually divide a terrain into 4, 9 or even 16 pieces as a final optimization. The latter could be slightly time consuming though.

Any recommendations for how I could speed this process? Right now I am just using the face selection mode and interactively grabbing and extracting sections with my mouse to progressively divide sections into halves. They don't all need to be the exact same size or shape, what's more important is being able to do it quickly.

[damaggio]

sorry but sometimes 3d can be tedious..i dont have a quicker solution...drag a box  over the mesh on top orthographic view to select faces , take your time ,you only have to do a few times....at least you are not painting skin weights on a character...that can make you wanna quit 3d.

[damaggio]

As a side note I hope you have a solution for texturing your terrain already, I'm just saying this because it would be better to have a texture before cutting to pieces I think.

[damaggio]

unless is procedural.

[Anonymous]

 "sorry but sometimes 3d can be tedious..i dont have a quicker solution..."

Thats fine. I just wanted to know if there was any obvious method to a more experienced Maya user. I think cutting it to 4,9,16 pieces should be manageable.

"As a side note I hope you have a solution for texturing your terrain already, I'm just saying this because it would be better to have a texture before cutting to pieces I think."

Oy. I'm not sure what my texturing solution is going to be, but the good news is I'm still in engine-development and planning my approach, and not creating my levels till I have everything figured out. I am making video tutorials for myself to remember the solutions we've been discussing for my various problems so I can use these approaches when I get down to business with level editing.

Any suggestions on terrain texturing approach? Procedural is most likely out for now, so I guess I am going to need one massive terrain texture that I can maybe load progressively. I probably have to do more research on this topic.