Mysteriously dissappearing mesh

[Ijon]

When looking at a mesh from certain positions and at certain angles it dissappears. Does anybody know why this happens? Here's a sample code with a square, that disappears when turning right (or setting the camera target to (4, 0, 1)):

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#include <irrlicht.h>
 
using namespace irr;
using namespace core;
using namespace scene;
using namespace video;
 
SColor const WHITE(255, 255, 255, 255);
 
int main() {
 
    IrrlichtDevice* irrDevice = createDevice(EDT_OPENGL, dimension2d<u32>(1600, 900), 32, false, false, false, 0); if (irrDevice == 0) return 1;
    ISceneManager* irrScene = irrDevice->getSceneManager();
    IVideoDriver* irrDriver = irrDevice->getVideoDriver();
    ICameraSceneNode* Camera = irrScene->addCameraSceneNodeFPS(0, 100.0f, 0.001f);
    Camera->setPosition(vector3df(1.1f, 1.0f, -0.6f));  /// When turning right from this position the mesh dissappears
    Camera->setTarget(vector3df(3, 0, 1));
 
    SMesh* Mesh = new SMesh;
    SMeshBuffer* TempBuff =  new SMeshBuffer();
    Mesh->addMeshBuffer(TempBuff);
    TempBuff->drop();
 
    TempBuff->Vertices.push_back(S3DVertex(vector3df(2, 0, 0), vector3df(0, 0, 0), WHITE, vector2df(0, 1)));
    TempBuff->Vertices.push_back(S3DVertex(vector3df(2, 1, 0), vector3df(0, 0, 0), WHITE, vector2df(0, 0)));
    TempBuff->Vertices.push_back(S3DVertex(vector3df(3, 0, 0), vector3df(0, 0, 0), WHITE, vector2df(1, 1)));
    TempBuff->Vertices.push_back(S3DVertex(vector3df(3, 1, 0), vector3df(0, 0, 0), WHITE, vector2df(1, 0)));
    TempBuff->Indices.push_back(0);  //┐
    TempBuff->Indices.push_back(1);  //├ 1st triangle
    TempBuff->Indices.push_back(2);  //┘                 1----3
    TempBuff->Indices.push_back(3);  //┐                 |    |
    TempBuff->Indices.push_back(2);  //├ 2nd triangle    |    |
    TempBuff->Indices.push_back(1);  //┘                 0----2
    TempBuff->setDirty(EBT_VERTEX_AND_INDEX);
 
    IMeshSceneNode* Meshnode = irrScene->addMeshSceneNode(Mesh);
 
    while(irrDevice->run()) {
        irrDriver->beginScene(true, true, SColor(255, 128, 128, 128));
        irrScene->drawAll();
        irrDriver->endScene();
    }
    Mesh->drop();
    irrDevice->drop();
    return 0;
}

[CuteAlien]

BackfaceCulling is by default enabled (meaning you don't see polygons from the backside).
Disable here with:

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TempBuff->getMaterial().BackfaceCulling = false;
 

Also the camera is very close to the polygon, so if you move a little closer it will vanish because of the near-clipping-plane of the camera frustum.

[Ijon]

It's neither a problem with backface culling nor with the near clipping plane. The whole mesh disappears instantly, this can also happen at greater distances, the coordinates in the code are just the only ones that I know exactly.

[CuteAlien]

Hm, yes - I see what you mean now. Although I haven't have it happen yet at greater distances. But something is strange indeed.

edit: It's the culling. With Meshnode->setAutomaticCulling(EAC_OFF) you could disable this. But the clean solution is recalculating the boundinboxes:

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TempBuff->recalculateBoundingBox();
 
Mesh->recalculateBoundingBox();
 

You have to do that whenever you change meshbuffer or mesh manually.

[Ijon]

It's the culling. With Meshnode->setAutomaticCulling(EAC_OFF) you could disable this. But the clean solution is recalculating the boundinboxes

I accept only clean solutions, of course.

In the original code I work with

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TempBuff->BoundingBox.addInternalPoint(...);

(Obviously I deleted a bit too much for the code sample.)

However, I didn't recalculate the bounding box of the mesh. I fixed this and now it works properly. Big thanks to you!