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Anddos

Drawing picked triangle

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For some reason i cannot render a triangle that represents the picked triangle

Not sure where i am going wrong, the picking is working fine just cant do this simple task...

 

void detect_picking()
{
    // get the current transform matrices
    D3DXMATRIX matProjection, matView, matWorld, matInverse;
    d3ddev->GetTransform(D3DTS_PROJECTION, &matProjection);
    d3ddev->GetTransform(D3DTS_VIEW, &matView);
    d3ddev->GetTransform(D3DTS_WORLD, &matWorld);
 
    // use the mouse coordinates to get the mouse angle
    GetCursorPos(&MousePos);
    float xAngle = (((2.0f * MousePos.x) / SCREEN_WIDTH) - 1.0f) / matProjection(0, 0);
    float yAngle = (((-2.0f * MousePos.y) / SCREEN_HEIGHT) + 1.0f) / matProjection(1, 1);
 
    D3DXVECTOR3 origin, direction;
    origin = D3DXVECTOR3(0.0f, 0.0f, 0.0f);
    direction = D3DXVECTOR3(xAngle, yAngle, 1.0f);
 
    // find the inverse matrix
    D3DXMatrixInverse(&matInverse, NULL, &(matWorld * matView));
 
    // convert origin and direction into model space
    D3DXVec3TransformCoord(&origin, &origin, &matInverse);
    D3DXVec3TransformNormal(&direction, &direction, &matInverse);
    D3DXVec3Normalize(&direction, &direction);
 
    // detect picking
    BOOL hit;
DWORD faceIndex;
 
    D3DXIntersect(meshTeapot, &origin, &direction, &hit, &faceIndex, NULL, NULL, NULL, NULL, NULL);
    if(hit)
{
  
   // Yes, draw the picked triangle in solid mode.
IDirect3DVertexBuffer9* vb = 0;
IDirect3DIndexBuffer9* ib = 0;
meshTeapot->GetVertexBuffer(&vb);
meshTeapot->GetIndexBuffer(&ib);
 
   d3ddev->SetIndices(ib);
d3ddev->SetStreamSource(0, vb, 0, sizeof(IDirect3DVertexBuffer9));
d3ddev->SetRenderState(D3DRS_FILLMODE,D3DFILL_SOLID);
 
// faceIndex identifies the picked triangle to draw.
d3ddev->DrawIndexedPrimitive(
D3DPT_TRIANGLELIST, 0, 0, meshTeapot->GetNumVertices(), faceIndex*3, 1);
}
else
{
        
}
}

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What doesn't work? What are you seeing?

 

Looking at the docs (you can do that, too!), the last SetStreamSource argument is Stride, i.e., the stride of a vertex in the buffer. You have sizeof a structure.

 

The stride for the vertex will be related to the vertex declaration (or you can derive it from the FVF). Also, look at the docs for ID3DXBaseMesh::GetNumBytesPerVertex()

 

EDIT: Also, you're assuming that the vertices are in index order in the vertex buffer. That may or may not be true. I.e., the 3 vertices forming the hit face are determined by the values in the index buffer for that face, and may/may not be sequential in the vertex buffer. E.g., the hit face may be form by vertex numbers 40, 63, 21.

 

EDIT2: In addition, to use DrawIndexedPrimitive you have to set an index buffer. It's been a while but I think in DX9, that's SetIndices.

 

You can google for "drawindexedprimitive example"

Edited by Buckeye

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Ive done  what you said,but its still not showing the triangle,i think its something todo with d3ddev->SetVertexDeclaration();

I am unsure how to retrieve the declaration from the mesh and then set device->SetVertexDeclaration for the retrieved value

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How about ID3DXBaseMesh::GetDeclaration.

Also, if you're rendering the triangle the same way like you draw the mesh, it won't make a difference visually. You need to play with different render states (say, disable lighting/texturing/depth and/or give a fixed color).

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