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indiocolifa

OpenGL Terrain Rendering Recommendation

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This is the first time i'm trying to render a terrain in OpenGL and I want some recommendations based on your experience with the topic. I want to represent a 2km square area. I'm using libnoise (great) to generate the heightmap. Current size is 512x512 pixels. First question: is this enough? I don't want high-quality geometry but I prefer high-quality texturing... May be 1024x1024 is better? Of course I'm currently rendering the terrain in "brute-force" mode (no realtime LOD), but i'm looking forward to implement some geomipmapping. In this respect, what is the best method for a good performance rendering 512x512 or 1024x1024 terrain geometry? For texturing I will use the following textures blended: 1) base texture 2) detail map 3) shadow map This is ok? What are your texturing approaches in terrain rendering? For shadow maps, there is some way to generate during level load with fast times? In realtime? Thank you very much for your help.

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So, I'd not recomment just heightmaps, because they aren't best for representing huge area (but 2 square kilometers ... well, maybe 1024 * 1024 would be enough). You're new to terrain rendering - try height mapping (also known as displacement mapping).
I'm using Clipmaps (very close technique to Carmack's Megatexture) to texturing terrain and to render terrain (well, it's pretty hard hit to performance, because you need to displace terrain in realtime - i'm using hardware displacement mapping on graphics cards, but you need fast GPU), often I use technique, which I call cell terrain mapping - The Elder Scrolls 4 : Oblivion used similar techniques - high polygon terrains in nearest cells and low poly in distance. Also you can try realtime voxelization of terrain.
Clipmapping is one of the best ways to texture terrain, but it needs a lot of hard drive space (with really big worlds like 50 * 50 km it needs several GigaBytes of COMPRESSED texture)! Texture blending is alternative for Clipmapping, but I didn't use it anymore. Another way is color mask (or another type of mask) texture mapping, it has very close to texture blending, but you can blend whole materials.
Shadow maps - well, it's a little complicated there. What quality do you need? Also you can combine "terrain shadow maps" with realtime shadow maps of sorrounding enviroment (something similar was in Gothic 3 from Piranha Bytes, very good game, but had a huge amount of bugs :( ). If you'd bake shadow maps before rendering (it doesn't matter, if in 3d modelling program like 3d studio, or during loading of application), you have to render every STATIC OBJECT on terrain and store that terrain shadow map (it may be huge F.e. 8192*8192 or more - if you'd update it, you can update it during time of "playing"). Then render (during "playing") standart dynamic shadow map for dynamic objects. In shader combine this two methods.
I'm using terrain cell mapping (or clipmapping), texturing using clipmaps, shadowing is all dynamic using realtime radiosity (it's very high hit to performance, but IT's one of the best solutions to get high quality lighting) and PCMLSM shadow mapping (I need very high quality lighting).

Well, i hope you can understand this, because I just got up from bed. Anyway happy new year to everyone.

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- For terrain LOD I'd use clipmaps, it is quite simple to implement and rather efficient technique.

- To generate normal map, you can use your noise generator library. In order to calculate the normal, you'll need several height samples around the point, much like in the same way as you'd calculate a normal for a triangle using cross-product.


//pseudo

CalculateNormal(int x,int y)
{

vector3 point1,point2,point3;

point1.set(0,0,heightmap.sample(x,y));
point2.set(1,0,heightmap.sample(x+1,y));
point3.set(0,1,heightmap.sample(x,y+1));

vector3 a = point2 - point1;
vector3 b = point3 - point1;

normal = crossproduct(a,b);
normalize(normal);

}




This is very simplistic method for the normal calculation and may result some artifacts, but should work for beginning.

GOod luck !!!

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Well I'm advancing with terrain rendering, already coded a gradient class for doing multiple point gradients. I used this for per-vertex coloring, which resulted in a colorful terrain, albeit without much features.

Now I want to ask some questions relating to texturing the terrain -- better than that, I will post my ideas and I would want to hear some opinions.

1. I will convert map every heightmap pixel to my color gradient arrays . This will be the base texture (1024x1024 or 512x512). Since it's basically plain color areas, what about using texture compression? Any benefit?

2. I'm getting very sharp highlight on the terrain (areas at full brightness, other at only ambient). Could this problem become from improper normal generation (i'm using libnoise normal-map from noise-map function), or I need to adjust OpenGL light parameters?

3. Should I bind/unbind the textures on every frame? I think I should not, but I ask just for it.

Thanks!

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Well' I've trying repeatedly to apply a texture to my terrain but I does not work, it gets with just one color... :(

Plz help me, tried hours without solution ..... :( :(

First, this is the texture generation code (this works, I've checked the values). Stores RGB values as follows:


void CTerrain::generateBaseTex(void)
{
float hmf;
SDL_Color final_color;

for (int x=0; x < tsize; x++)
for (int y=0; y < tsize; y++)
{
hmf = hmap.GetValue(x,y);
if (hmf < -1.0f)
hmf = -1.0f;
else
if (hmf > 1.0f)
hmf = 1.0f;

final_color = base_grad->GetColor((int)((hmf+1)*127.5f) );

base_tex[((x*tsize+y)*4)] = (GLubyte) final_color.r;
base_tex[((x*tsize+y)*4)+1] = (GLubyte)final_color.g;
base_tex[((x*tsize+y)*4)+2] = (GLubyte)final_color.b;
}

}



Now for the brute force rendering...


void CTerrain::Render()
{
// renders terrain from height map
// terrain origin is at 0,0,0

float v_height; // vertex height
GLfloat scaledHeight;
static float eye;

eye = eye + 0.1f;

glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.0f, 1.0f, 1.0f, 1200.0f);

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt (0.0f, 200.0f, eye, 128.0f, 0.0f, 128.0f, 0.0f, 1.0f, 0.0f);

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

GLfloat lightpos[4] = { 128.0f, -100.0f, 128.0f, 0 };

//glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);
glLightfv(0, GL_POSITION, lightpos);

glTranslatef(0.0f, 0.0f, 0.0f);

glEnable( GL_TEXTURE_2D );
glGenTextures (1, &texnames);
glBindTexture (GL_TEXTURE_2D, texnames);
glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
glTexParameteri (GL_TEXTURE_2D, GL_GENERATE_MIPMAP, GL_TRUE);
glTexImage2D (GL_TEXTURE_2D, 0, GL_RGB, tsize, tsize, 0, GL_RGB, GL_UNSIGNED_BYTE, base_tex);
glTexEnvf (GL_TEXTURE_2D, GL_TEXTURE_ENV_MODE, GL_MODULATE);

// render (this is BRUTE FORCE)

for (int z = 0; z < tsize-1; z++)
{
glBegin(GL_TRIANGLE_STRIP);

for (int x=0; x < tsize-1; x++)
{
v_height = hmap.GetValue(x,z);
scaledHeight = v_height * h_scale;

glNormal3b (nrmap.GetValue(x,z).red, nrmap.GetValue(x,z).green, nrmap.GetValue(x,z).blue);
glTexCoord2d( (GLdouble)(x/tsize), (GLdouble)(z/tsize) );
glVertex3f ((GLfloat) x, scaledHeight, (GLfloat) z);

v_height = hmap.GetValue(x,z+1);
scaledHeight = v_height * h_scale;

glNormal3b(nrmap.GetValue(x,z+1).red, nrmap.GetValue(x,z+1).green, nrmap.GetValue(x,z+1).blue);
glTexCoord2d( (GLdouble)(x/tsize), (GLdouble)((z+1)/tsize) );
glVertex3f ((GLfloat)x, scaledHeight, (GLfloat)z+1);
}
glEnd();
}
}



Thx!




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You may also want to see "terrain splatting". It is just texturing the terrain with several 256x256 textures... Tiling, but looks pretty good, and most of the terrain engines still use splatting, not those fancy MegaTextures.

Sharp shadows could be caused by too large normals.

BTW, normals:
Derived from cross products, simple and efficient:

normal.z=2;
normal.x=heightmap.sample(x-1,y)-heightmap.sample(x+1,y);
normal.y=heightmap.sample(x,y-1)-heightmap.sample(x,y+1);
Normalize(normal);

I guess its better and cheaper than cross produtcts.

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