Smart Terrain Rendering with Xna using Billod algorithm

re: Smart Terrain Rendering with Xna using Billod algorithm

valentin — Thu, 05 Nov 2009 20:14:41 GMT

thx you for your great help :)

i will correct this bug so :)

re: Smart Terrain Rendering with Xna using Billod algorithm

raygeee — Thu, 05 Nov 2009 16:45:09 GMT

hi,

first of all thanks for sharing the code and the thorough explanation.

While integrating it into my project I found an ugly little bug:

Suppose your quadtree is located at (0,0,0) and the width of the heightmap is 256. Then the far out vertex defining the quadtree should be located at (255,y,255) - it's not. It's at (256,y,256) which results in having two bad shaped sides of the quadtree.

To fix this I had to change 2 lines in QuadNode.cs:

in Initialize() replace

float size = GetNodeSize();

with

float size = GetNodeSize() - 1;

and in AddChild(NodeChild position, NodeContent flag) replace

float size = node.GetNodeSize();

with

float size = node.GetNodeSize() - 1;

So far this worked for me although with 4 quadtrees I still have a little gap between the quadtrees because the vertex positions aren't the same.

Cheers, raygeee

Tutoriaux Xna Game Studio : sommaire général

Graphic Stream — Fri, 19 Jun 2009 14:36:53 GMT

(Tutoriaux adaptés au Xna Game Studio 3.1) Première partie : Apprentissage XNA Tutorial

re: Smart Terrain Rendering with Xna using Billod algorithm

valentin — Fri, 01 May 2009 09:01:55 GMT

Bert > I used to think it was that problem. Great good job

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re: Smart Terrain Rendering with Xna using Billod algorithm

Bert — Mon, 27 Apr 2009 14:45:43 GMT

I have solved the problem :). It appears I have made a mistake in my own code due which the tree's where not correctly positioned.

Thanks for you help!

re: Smart Terrain Rendering with Xna using Billod algorithm

valentin — Thu, 23 Apr 2009 06:51:33 GMT

but the trees are following the shape of the mountains ?

so you just have to reduce the height maybe.

you can send me your code here : lord.asriel [@] free dot fr

re: Smart Terrain Rendering with Xna using Billod algorithm

Bert — Wed, 22 Apr 2009 15:00:56 GMT

Well I know that i have the right triangle from the quadtree, but when I try to get the height of the point in the triangle, I don't get the right height.... All of the trees float above the terrain.

re: Smart Terrain Rendering with Xna using Billod algorithm

valentin — Wed, 22 Apr 2009 06:00:05 GMT

you have to know the exact position of your tree inside the triangle that contains the X, Z position of your tree,

right ?

re: Smart Terrain Rendering with Xna using Billod algorithm

Bert — Tue, 21 Apr 2009 13:41:42 GMT

Well maybe my question was not that clear...

But the problem is that I need to place tree's( 3D model ) on the terrain. However I find it quite hard to get the height of a certain point on the quadtree.

Therefore I lookup the childNode that contains the point of which I need to get the height. When I have found the child node containing that point, I look up which triangle contains the point of which I want to know the height. And then I calculate the height of the point in that triangle.

Since the terrain is rendered with the help of the vertices it should give the exact height of the terrain on that point...

I'm sorry that I can not give a better description of the problem.

re: Smart Terrain Rendering with Xna using Billod algorithm

valentin — Tue, 21 Apr 2009 12:30:45 GMT

by tree you mean the objet model Tree (like flower, grass ect.) ?

I first think that you were speaking about quad tree so it was hard to understand your problem :)

you only have to substract a delta that you have to substract to the height of each tree.

I dont understand your point 2 "Measure the altitude between the point in the triangle and 0".

re: Smart Terrain Rendering with Xna using Billod algorithm

valentin — Mon, 20 Apr 2009 16:26:09 GMT

i saw your question

i will try to answer tomorrow :)

re: Smart Terrain Rendering with Xna using Billod algorithm

Bert — Mon, 20 Apr 2009 13:27:59 GMT

I am trying to use the code of this project in order to build an terrain with tree's. However when I try to place a tree on a certain position on the quadtree it appears to be floating in the air.

I noticed that the QuadTree.GetHeight()-method is not that exact, therefore I try to calculate the height on my own with the following steps:

1. Locate the triangle which contains the point

2. Measure the altitude between the point in the triangle and 0

This almost gives me the correct height, because I can see the trees following the shape of the mountains, how ever they still appear to be floating....

Does anyone have an idea how I can solve this?

re: Smart Terrain Rendering with Xna using Billod algorithm

valentin — Tue, 24 Mar 2009 08:59:29 GMT

that's great :) send me your code so that i can see :)

re: Smart Terrain Rendering with Xna using Billod algorithm

Armigus — Thu, 19 Mar 2009 01:35:54 GMT

I'm actually getting some results with improving the terrain rendering, to the point of wanting the camera to maintain a bounding frustum and check the node children against it.

The QuadNode class needs some refactoring first:

public TerrainVertex SetVertex(float x, float z, Vector3 n)

{

VertexPositionNormalTexture v0 = new VertexPositionNormalTexture ();

v0.Position = new Vector3(x, ParentTree.GetHeight(x, z), z);

v0.Normal = n;

v0.TextureCoordinate = GetTextureCoordinates(x, z);

return new TerrainVertex(v0);

}

public Vector3 GetNormal(Vector3 nw, Vector3 ne, Vector3 sw, Vector3 se)

{

Vector3 n = new Plane(nw, ne, se).Normal * new Plane(nw, se, sw).Normal;

n.Normalize();

return n;

}

public Vector3 GetNormal(float left, float right, float top, float bottom)

{

Vector3 nwp = new Vector3(left, ParentTree.GetHeight(left, top), top);

Vector3 nep = new Vector3(right, ParentTree.GetHeight(right, top), top);

Vector3 swp = new Vector3(left, ParentTree.GetHeight(left, bottom), bottom);

Vector3 sep = new Vector3(right, ParentTree.GetHeight(right, bottom), bottom);

return GetNormal(nwp, nep, swp, sep);

}

public Vector3 GetNormal(TerrainVertex nw, TerrainVertex ne, TerrainVertex sw, TerrainVertex se)

{

Vector3 nwp = nw.Value.Position();

Vector3 nep = ne.Value.Position();

Vector3 swp = sw.Value.Position();

Vector3 sep = se.Value.Position();

return GetNormal(nwp, nep, swp, sep);

}

This will simplify the Initialize method considerably:

public void Initialize()

{

float size = GetNodeSize();

float x = Location.X;

float z = Location.Y;

float xWhole = x + size;

float zWhole = z + size;

float zHalf = z + size / 2;

float xHalf = x + size / 2;

//normal of the current quad

Vector3 normal = GetNormal(x, xWhole, z, zWhole);

//first compute the 4 egdes of the current square

//here we know all : position and height.

{

if (Parent != null)

{

//if we have a parent maybe

re: Smart Terrain Rendering with Xna using Billod algorithm

Mohammad — Tue, 03 Mar 2009 03:54:25 GMT

Wow! You are man! This is exactly what I was looking for!

re: Smart Terrain Rendering with Xna using Billod algorithm

valentin — Sat, 28 Feb 2009 07:45:05 GMT

yes you just have tu replace in all the projet.

For the generic i dont use it beacause if you want to make a special operation on vertex you will have to cast or try generic operation that cost more cpu than direct operation.

In Xna, code optimization are not the best optimization...

Hmmm.... generics might be an option after all

Armigus — Sat, 28 Feb 2009 05:47:34 GMT

If you need define a generic class so that the item is indeed a value type you could have

public class QuadTree<T> : QuadNodeCollection, IDisposable where T : struct

You would then have to convert all classes that refer to vertex structures to generics, a task in and of itself. I haven't tested this theory yet so no guarantees.

BTW, check out what Dragoon did with Reimer's material (dracocepheus.blogspot.com). It's a component-based project. Since I eventually want a full game engine I am trying to pull together GameComponent items that can be registered as services.

re: Smart Terrain Rendering with Xna using Billod algorithm

Armigus — Sat, 28 Feb 2009 04:11:28 GMT

If you want the terrain to render using a customized vertex format and a custom shader, isn't it necessary to replace the vertex type project-wide? It's not like you can have a generic vertex struct Vertex<T> and have XNA recognize it because generics are not value types by default. C# has no equivalent of VB's ByVal to force a value type either.

re: Smart Terrain Rendering with Xna using Billod algorithm

valentin — Wed, 25 Feb 2009 13:52:15 GMT

can't figure why too :)

did you change all my VertexPositionNormalTexture by your own vertex structure type ?

A blank screen is a common answer to this kind of mistake