Thread: Conceptual Problem in D3D - Tranformations

So I am trying to demonstrate the phenomenon of moire fringes in d3d, because I hope to model the fringes in 3d using rapid prototyping in a cse class i'm taking

http://www.jstor.org/view/07468342/di020744/02p0043o/0

So but basically, I'm just trying to simulate the concept of two screens running by each other.

I have two sets of lines in two different vertex buffers.

What I want to do is quite like this image

http://www.jstor.org/cgi-bin/jstor/g.../18b.jpg?jstor

I have something like this

Code:

	pd3dDevice->BeginScene();

	static float i = 0.0;
	i += 0.01;

	D3DXMATRIX mWorld, mView;
	D3DXMatrixRotationY( &mView, i );
	D3DXMatrixTranslation( &mWorld, 0.0f, 0.0f, 5.0f );

	pd3dDevice->SetTransform( D3DTS_WORLD, &mWorld );
	pd3dDevice->SetFVF( D3DFVF_MY_VERTEX );

	pd3dDevice->SetStreamSource( 0, pCircleList, 0, sizeof(Vertex) );
	pd3dDevice->DrawPrimitive( D3DPT_LINELIST, 0, (67 * 720) / 2);

	pd3dDevice->SetTransform( D3DTS_WORLD, &mView );

	pd3dDevice->SetStreamSource( 0, pLineList, 0, sizeof(Vertex) );
	pd3dDevice->DrawPrimitive( D3DPT_LINELIST, 0, (300) / 2);

	pd3dDevice->EndScene();

This has the intention of only rotating one set of lines, but the whole world gets flipped around when I apply the rotation. I just want one of the two sets of lines to rotate around the z. Tipz

You need to rotate the object representing the lines first.

Code:

D3DXMATRIX mWorld, mView;
	D3DXMatrixRotationY( &mView, i );
	D3DXMatrixTranslation( &mWorld, 0.0f, 0.0f, 5.0f );

	pd3dDevice->SetTransform( D3DTS_WORLD, &mWorld );
	pd3dDevice->SetFVF( D3DFVF_MY_VERTEX );

	pd3dDevice->SetStreamSource( 0, pCircleList, 0, sizeof(Vertex) );
	pd3dDevice->DrawPrimitive( D3DPT_LINELIST, 0, (67 * 720) / 2);

	pd3dDevice->SetTransform( D3DTS_WORLD, &mView );

You are setting the world matrix for the object to the view matrix which is incorrect. You need to create an object representing the line grid and then create 2 of these objects. Each of these then will have their own world transformations.

Based on your setup you seem a bit fuzzy on how 3D transformations work. I suggest doing some research on the topic for further understanding.

Here is how I would do it:

Code:

class LineGrid
{
  public:
     ...
     void Render();

  private:
     D3DXVECTOR3 m_vecPos;
     D3DXVECTOR3 m_vecRot;
     D3DXVECTOR3 m_vecScale;
    
};
...
void LineGrid::Render()
{
  D3DXMATRIX matWorld,matTrans,matRot,matScale;

  //Scale
  D3DXMatrixScaling(&matScale,m_vecScale.x,m_vecScale.y,m_vecScale.z);

  //Rotate - will suffer gimble lock
  D3DXMatrixRotationYawPitchRoll(&matRot,m_vecRot.x,m_vecRot.y,m_vecRot.z);

  //Translate
  D3DXMatrixTranslation(&matTrans,m_vecPos.x,m_vecPos.y,m_vecPos.z);

  //Concatenate - order is important
  //If you translate then rotate, rotation is around new position
  //If you rotate then translate, rotation is around 0,0,0
  //You may wish to do both depending on the application

  //Scale in model space
  //Rotate in model space 
  //Translate to position
  matWorld=matScale*matRot*matTrans;

  //Set world transform
  m_pDevice->SetTransform(D3DTS_WORLD,&matWorld);

  //Draw object
  ...
  ...
}
  
...
...
void My3DApp::Render()
{
   //Set view matrix
   m_pDevice->SetTransform(D3DTS_VIEW,m_pCameraMgr->GetActiveCamera());

   //Render line grid objects
   ...
   ...
   for (int i=0;i<static_cast<int>(vLineGrids.size());i++)
   {
      vLineGrids[i]->Render();
   }
   ...
   ...
}

Thanks. Probably should go over stuff but I'm just being a hack.