Connecting terrein nodes

[diho]

Hello everyone,

I have a question regarding multiple terrain nodes. I have 4 terrain nodes with each a part of a heightmap that should connect to each other. Sadly when I render it, the different terrains dont connect and there are height differences.

Does someone know a solution to this problem?

-Diho

[Mel]

Use the addTerrainMesh method instead. The geomipmap terrain nodes are currently sort of almost a legacy feature, as the terrain meshes are the same fast and can be stored statically on the video card with a very small impact on performance, and use less memory, compared to the terrain nodes. If you're going to use a large terrain, the terrain node goes well, if you're using smaller terrains from textures, go for the terrain meshes instead, and set them to be static meshes

[Seven]

also, the terrain scenenode has some requirements for creation that are not obvious.

Code: Select all

 
    //! A scene node for displaying terrain using the geo mip map algorithm.
    /** The code for the TerrainSceneNode is based on the Terrain renderer by Soconne and
     * the GeoMipMapSceneNode developed by Spintz. They made their code available for Irrlicht
     * and allowed it to be distributed under this licence. I only modified some parts.
     * A lot of thanks go to them.
     *
     * This scene node is capable of very quickly loading
     * terrains and updating the indices at runtime to enable viewing very large terrains. It uses a
     * CLOD (Continuous Level of Detail) algorithm which updates the indices for each patch based on
     * a LOD (Level of Detail) which is determined based on a patch's distance from the camera.
     *
     * The Patch Size of the terrain must always be a size of ( 2^N+1, i.e. 8+1(9), 16+1(17), etc. ).
     * The MaxLOD available is directly dependent on the patch size of the terrain. LOD 0 contains all
     * of the indices to draw all the triangles at the max detail for a patch. As each LOD goes up by 1
     * the step taken, in generating indices increases by - 2^LOD, so for LOD 1, the step taken is 2, for
     * LOD 2, the step taken is 4, LOD 3 - 8, etc. The step can be no larger than the size of the patch,
     * so having a LOD of 8, with a patch size of 17, is asking the algoritm to generate indices every
     * 2^8 ( 256 ) vertices, which is not possible with a patch size of 17. The maximum LOD for a patch
     * size of 17 is 2^4 ( 16 ). So, with a MaxLOD of 5, you'll have LOD 0 ( full detail ), LOD 1 ( every
     * 2 vertices ), LOD 2 ( every 4 vertices ), LOD 3 ( every 8 vertices ) and LOD 4 ( every 16 vertices ).
     **/
 

if the bitmap size does not match up with the patch size then, when trying to align nodes together, there will be some error.

[diho]

@Mel, @Seven, Thanks for your replies!

[diho]

I successfully managed to connect multiple terrain nodes to each other, but at a certain distance from the seam, you can see a few gaps between the two connecting terrain nodes.

Here you can see the gaps


But when I move closer, they are gone.


Does anyone know how to fix this? I have already played a bit with different LOD and smoothing levels but that doesn't seem to solve it.

-Diho

[hendu]

You're asking for their LODs at the seam to be the same. I don't think it has logic for that, it's intended to contain the entire terrain; I'd look into alternative solutions, like static terrain meshes.

[diho]

There has to be a better solution than using static terrain meshes. In the comment of Spintz http://irrlicht.sourceforge.net/forum/v ... 29#p114529 he describes that a possible solution is to make sure that every terrain scene node has the same lod level at it's edges/borders.

Does anyone know where to start? My guess is that I have to look at the preRenderLODCalculations function inside the CTerrainSceneNode.cpp file.

[diho]

I found the solution, it's quite simple to be honest.

in CTerrainSceneNode.cpp around line 640 you can find this piece of code:

Code: Select all

for (s32 j = 0; j < count; ++j)
        {
            if (frustum->getBoundingBox().intersectsWithBox(TerrainData.Patches[j].BoundingBox))
            {
                const f32 distance = cameraPosition.getDistanceFromSQ(TerrainData.Patches[j].Center);
 
                TerrainData.Patches[j].CurrentLOD = 0;
                for (s32 i = TerrainData.MaxLOD - 1; i>0; --i)
                {
                    if (distance >= TerrainData.LODDistanceThreshold[i])
                    {
                        TerrainData.Patches[j].CurrentLOD = i;
                        break;
                    }
                }
            }
            else
            {
                TerrainData.Patches[j].CurrentLOD = -1;
            }
        }

The only thing you need to add are two single lines of code:

Code: Select all

if (j < 16 || j > (count - 16) || j % 16 == 0 || (j % 15) == (floor(j / 15) - 1))
                    continue;

resulting in the following piece of code:

Code: Select all

for (s32 j = 0; j < count; ++j)
        {
            if (frustum->getBoundingBox().intersectsWithBox(TerrainData.Patches[j].BoundingBox))
            {
                const f32 distance = cameraPosition.getDistanceFromSQ(TerrainData.Patches[j].Center);
 
                TerrainData.Patches[j].CurrentLOD = 0;
                //border patches should be the same
 
                if (j < 16 || j > (count - 16) || j % 16 == 0 || (j % 15) == (floor(j / 15) - 1))
                    continue;
 
                for (s32 i = TerrainData.MaxLOD - 1; i>0; --i)
                {
                    if (distance >= TerrainData.LODDistanceThreshold[i])
                    {
                        TerrainData.Patches[j].CurrentLOD = i;
                        break;
                    }
                }
            }
            else
            {
                TerrainData.Patches[j].CurrentLOD = -1;
            }
        }

These two lines make sure that ever patch at the border of a terrain node keep the same lod level (0 at the moment). I hope someone finds this useful

[CuteAlien]

Thanks for the info. Do you have maybe already written a small test-application which shows exactly this problem? In that case it would be cool if you could post that one as well.

[diho]

Sure, I will add an example, as soon as I have some time, to the code snippet board and leave a link here.

[diho]

As promised: http://irrlicht.sourceforge.net/forum/viewtopic.php?f=9&t=51220

-Diho

[CuteAlien]

Thank you! All discussion continuing in the http://irrlicht.sourceforge.net/forum/v ... =9&t=51220 thread. Locking this one.