Moving and Imported model along the forward Vector - DirectX11 C++

Question

I have spent ages trying to work out the way to create the forward vector of any imported object, This is so that I can complete the players controls and also add billboarding. This is for a University project where I have been given a set GameObject class to load in the objects using a MeshLoader and OBJLoader class. I currently am using A .GetWorld(); which returns me an XMFLOAT4X4 which should give me the data of the object in the world. I then convert it to a XMMATRIX using the XMLoadFloat4X4 and then grab each row of data from that matrix into its own XMVECTOR. I have tested these and Believe that they are in the correct order but am still having the problem of my character never moving when I hit the forward key. I wondered If I am doing anything completely wrong or if I have just missed something out.

else if (GetAsyncKeyState(VK_UP))
{
    XMFLOAT4X4 currrentWorld = _zaz.GetWorld();
    XMMATRIX currentWorldM = XMLoadFloat4x4(&currrentWorld);

    XMVECTOR scale = currentWorldM.r[1];
    XMVECTOR rotation = currentWorldM.r[2];
    XMVECTOR translation = currentWorldM.r[3];
    XMVECTOR forward = currentWorldM.r[4];

    forward = XMVector3Normalize(forward);

    translation = XMVectorAdd(translation, forward);

    newWorld = XMMATRIX(scale, rotation, translation, forward);

    _zaz.SetWorld(&newWorld);
    _zaz.UpdateWorld();
}

The other problem is that “_zaz.UpdateWorld(); only seems to work inside my update method even though all Keyboard controls are checked on update.

void GameObject::UpdateWorld()
{
    XMMATRIX scale = XMLoadFloat4x4(&_scale);
    XMMATRIX rotate = XMLoadFloat4x4(&_rotate);
    XMMATRIX translate = XMLoadFloat4x4(&_translate);

    XMStoreFloat4x4(&_world, scale * rotate * translate);
}

void GameObject::SetWorld(XMMATRIX* world)
{
    XMStoreFloat4x4(&_world, *world);
}

It is definitely reading in the values, I get the game to break on the key “up” being pressed which should run the above code. All of the values are set. The car does currently rotate and If I rotate the car slightly and then break the game only the rotation and forward vectors change, Which should be ok?

The watch of all of the vectors after the second iteration of the elseif keypressed up code is called

If you have any Ideas it would help massively.

I assumed that It would be similar to:

else if (GetAsyncKeyState(VK_CONTROL))
{
    XMFLOAT4 position = _cameraFree.GetEye();
    XMFLOAT4 direction = _cameraFree.GetForward();

    position.x -= (direction.x * 0.05f);
    position.y -= (direction.y * 0.05f);
    position.z -= (direction.z * 0.05f);

    _cameraFree.SetEye(position);
    _cameraFree.CalculateViewProjection();
}

Which uses XMFLOAT4's for the cameras data, which was easy to do, With the XMFLOAT4X4's and XMMATRIX's that my GameObject rely on it has so far been impossible to get to work. If there is anymore info that I can supply to help then please say!

Hope this helps you help me.

Answer 1

The way you imagine currentWorldM is completely wrong.

First, you do an out of bound access, XMMATRIX::r is only 4 elements, the valid range is [0..3].

Second, a 4x4 matrix is not built like that, it contains everything merged, you have to see it more like a frame, with 3 vectors i j k and a position O. One of them is your forward vector, one up and one right ( or left ).

A scale matrix is for example in r[0].x r[1].y and r[2].z, and this is only true as long as you do not concatenate it with a rotation, after that, it will be spread over the full matrix.