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Selecting Meshes with mouse

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I'm wondering if there were more *. file meshes rendering how is the mouse picking (selecting) implemented. e.g. When I click on mesh to select it.

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If you've got an older version of the SDK...(maybe even last year's?) It's got a "pick" sample Direct3D project which shows how to do this.

I know it's in the DX81 SDK samples for sure.


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With optimizations aside, you "pick" both and select the one with shorter distance.

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hi, using D3DX functions, it's not that hard.
The first step is to get the starting position and a direction in world space :

D3DVIEWPORT9 viewPort;


D3DXVECTOR3 start((float)mousePos.x, (float)mousePos.y, 0.0f);
D3DXVECTOR3 end((float)mousePos.x, (float)mousePos.y, 1.0f);

D3DXVec3Unproject(&start, &start, &viewPort, g_Camera.GetProjectionMatrix(), g_Camera.GetViewMatrix(), &id);
D3DXVec3Unproject(&end, &end, &viewPort, g_Camera.GetProjectionMatrix(), g_Camera.GetViewMatrix(), &id);
dir = end - start;
D3DXVec3Normalize(&dir, &dir);

where mousePos is your mouse position in screen space.

After that, you only need to use D3DX functions like :

D3DXIntersect // intersect a .x mesh
D3DXIntersectSubset // intersect a subset of a .x mesh
D3DXIntersectTri // intersect a single triangle

In my code, I use D3DXIntersectTri, because I don't use .x meshes, so here is the code for the actual intersection test :

D3DXVECTOR3 tDir; // transformed direction
D3DXVECTOR3 tStart; // transformed starting position

// transforme using inverse of the mesh's tranform matrix. If you don't
// do that, the intersection will be wrong if the world matrix for this
// mesh is not identity
D3DXVec3TransformNormal(&tDir, dir, &m_InverseWorldMatrix);
D3DXVec3TransformCoord(&tStart, start, &m_InverseWorldMatrix);

// I skeep the locking of the buffers, the loops, ect. Here, you just give
// the 3 D3DXVECTIR3 of the triangles (p0 ... P2), the starting point and
// direction (transformed ones), pointer to 3 floats : U, V and dist (read
// the doc to know what it is if you don't ^^)
if (D3DXIntersectTri(&p0, &p1, &p2, &tStart, &tDir, &U, &V, dist))

Before testing every triangle, I also do a simple bouding sphere test, and then a bouding box test to optimize. You use these 2 functions for that :


Ok, I think i didn't forget anything, if you have other questions, feel free to ask ^^

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