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How to put a model in the "world of the camera" ?

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[excuse my English] I have the ambitious objective to manage a day to make a space simulation. But for the moment I'm a newbie, and there are problems with my camera... I try to display a starfield. I know the idea of the "skybox" or "sphere", but I think have a better idea : render a "rectangle" in the bottom of the view, and move the texture (the universe, with stars, planets...) on this rectangle. But I don't know how to put the rectangle in the world of the camera, and not in the world of the scene. My test program resembles that :
      
D3DXMATRIX matView, matTranslate, matResult;
 
 
// Put a camera which moves on the right

 
D3DXMatrixLookAtLH( &matView, &D3DXVECTOR3( 0.0f + right, 0.0f, -500.0f),
&D3DXVECTOR3( 0.0f, 0.0f, 0.0f ),
&D3DXVECTOR3( 0.0f, 1.0f, 0.0f ));
 
 
// Translate the rectangle in the bottom

 
D3DXMatrixTranslation(&matTranslate, 0.0f, 0.0f, 900.0f);
 
 
// Say to make the translation of the model compared to the origin (0, 0, 0) of the camera

// and not compared to the origin of the scene, to keep the rectangle in the view

 
???
I tried several things, but without success
 
 
// Create the view

 
m_pd3dDevice->SetTransform(D3DTS_VIEW, &matResult);
 
 
// Render of the rectangle

 
...
      
Can you explain me how to fix a model to a camera ? Thanks... Edited by - Coudrak on November 3, 2001 5:40:28 AM

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You want to keep your rectangle always facing your camera , right? This technique is called billboarding, and is used for particle effects and other things. The direct x sdk comes with a billboarding sample that renders a bunch of trees as textured quads. Take a look at that sample, or search this and other sites for billboarding tutorials.

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Nooo, it's not exactly that

The rectangle must remain aligned with the view, yes, but it must also move itself like the camera. Because I would like have a backgound in fact.

And with this example (that I found in this forum)...

--------
// Get the current view matrix
D3DXMATRIX matView;

m_pd3dDevice->GetTransform(D3DTS_VIEW, &matView);

// Get the transposed matrix

D3DXMATRIX matTransposed;
D3DXMatrixTranspose(&matTransposed, &matView);

// Position the billboard
matTransposed._41 = X;
matTransposed._42 = Y;
matTransposed._43 = Z;

// Set as world transformation matrix
m_pd3dDevice->SetTransform(D3DTS_WORLD, &matTransposed);

// Draw whatever - will be aligned with view
----

... the problem is the coordinates (X, Y, Z) to place the rectangle are scene coordinates, and not camera coordinates. I would like when I move the camera, that the rectangle remains "hung" with the camera, to make a backgound 2D...


Edited by - Coudrak on November 4, 2001 6:47:25 AM

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Hi,

I understand what you''re trying to do, and the solution is to take a simple object matrix and multiply it with the inverse view matrix, to get the final transformation matrix in world space..

In this example I just set the object as being 200 units away from the camera

  
// how to lock an object into a position in front of the camera

D3DMATRIX object;
D3DUtil_SetIdentityMatrix( object );
object(3,2) = 200.0f; // move the object away from the cam down the z axis 200 units

D3DMath_MatrixMultiply( finaltrans, InverseViewMatrix , object );


I think you already know how to get the inverse view matrix, and set the finaltrans matrix as the currect transform.

Cheers

Matt



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