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Problem with Translation and Rotation in DirectX


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#1 Medo3337   Members   -  Reputation: 665

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Posted 06 May 2012 - 10:15 AM

I have made a tank model, now I am trying to make the tank move FORWARD and then stop and rotate around itself to change its position then move forward again.

When I rotate the tank and change the Z axis to move it forward, it doesn't move FORWARD, it move in another position.

The code is similar to the following:

D3DXMATRIX matRot;
D3DXMATRIX matCenter;
D3DXMATRIX matScale;

D3DXMatrixTranslation(&matCenter, 0.0f, 0.0f, 0.0f); // *** Rotation point ***
D3DXMatrixTranslation(&matPos, tankPosX, -240.0f, tankPosZ);
D3DXMatrixRotationYawPitchRoll(&matRot, D3DXToRadian(tankRotX), D3DXToRadian(0.0f), D3DXToRadian(0.0f));
D3DXMatrixScaling(&matScale, 1.0f, 1.0f, 1.0f);

d3ddev->SetTransform(D3DTS_WORLD, &(matScale * matCenter * matRot * matPos));

Edited by Medo3337, 06 May 2012 - 10:16 AM.


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#2 leonard2012   Members   -  Reputation: 167

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Posted 06 May 2012 - 08:38 PM

You may try to reverse the sign of tankPosZ to see what it's alike. Remember that Direct3D camera looking at positve z-axis, which is opposite to OpenGL.

#3 iedoc   Members   -  Reputation: 966

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Posted 06 May 2012 - 10:11 PM

are you sure your adding to the tanks forward correctly? i mean, if you want the tank to move forward (+z in tank space), and only add to the tanks z axis, it will move towards the +z in world space, no matter which way your tank is facing or how you rotated it. working with vectors for these kinds of things work well. so, when you rotate the tank, you should also rotate the tanks "forward" vector, then just add that forward vector to the tanks final position, something like this:

D3DXMATRIX matRot;

D3DXMATRIX matCenter;

D3DXMATRIX matScale;

D3DXMATRIX posZUnitVec;

D3DXVECTOR3 vecTankForward;


D3DXMatrixRotationYawPitchRoll(&matRot, D3DXToRadian(tankRotX), D3DXToRadian(0.0f), D3DXToRadian(0.0f));

D3DXMatrixTranslation(&posZUnitVec, 0.0f, 0.0f, 1.0f); // matrix holding position of vector pointing to positive z

D3DXMATRIX m = posZUinitVec * matRot;

vecTankForward = D3DXVECTOR3(m._41,m._42,m._43); // Get vector from the matrix


// move the tank forward (speed is the speed you want to move the tank every time this function is called)

tankPosX += speed * vecTankForward.x;

tankPosZ += speed * vecTankForward.z;


D3DXMatrixTranslation(&matCenter, 0.0f, 0.0f, 0.0f); // *** Rotation point ***

D3DXMatrixTranslation(&matPos, tankPosX, -240.0f, tankPosZ);

D3DXMatrixScaling(&matScale, 1.0f, 1.0f, 1.0f);


d3ddev->SetTransform(D3DTS_WORLD, &(matScale * matCenter * matRot * matPos));


Edited by iedoc, 06 May 2012 - 10:13 PM.

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#4 Medo3337   Members   -  Reputation: 665

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Posted 07 May 2012 - 12:16 AM

@iedoc:That works perfectly! there is still one problem, If I am trying to apply that on airstrike as well, when the airstrike LOOK UP, it will NOT move up, I mean I want to update the rotation on any Axis (X, Y or Z) and the model still move FORWARD, if the model front is pointed up, the model should go up on Y axis while moving forward, so the airstrike can take off and start flying.

#5 iedoc   Members   -  Reputation: 966

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Posted 07 May 2012 - 07:13 AM

not sure if you've tried this, but you will also have to add the y component of the "forward" vector to the things position. I only added the x and z above. so you need to do this:


tankPosX += speed * vecTankForward.x;

tankPosY += speed * vecTankForward.y;

tankPosZ += speed * vecTankForward.z;


D3DXMatrixTranslation(&matPos, tankPosX, tankPosY, tankPosZ);


Edited by iedoc, 07 May 2012 - 07:13 AM.

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#6 Medo3337   Members   -  Reputation: 665

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Posted 07 May 2012 - 11:56 PM

Yeah, I tried this before I posted, but it makes the mesh move up even if its not pointed up since you increase the Y axis even if the mesh is moving straight on the ground!

So I tried to check for rotation on Yaw before changing the position on Y axis:

tankPosX += speed * vecTankForward.x;
if (rotYaw != 1.0f)
tankPosY += speed * vecTankForward.y;
tankPosZ += speed * vecTankForward.z;

D3DXMatrixTranslation(&matPos, tankPosX, tankPosY, tankPosZ);

However, I am not very sure if this will work fine on any mesh, airstrike, tank, human, helicopter, etc...

Edited by Medo3337, 08 May 2012 - 12:30 AM.





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