Setting Up a Projection Matrix

Article
06/30/2006

The following ProjectionMatrix sample function, written in C++, takes four input parameters that set the front and back clipping planes, as well as the horizontal and vertical field of view angles. This code parallels the approach discussed in the What Is the Projection Transformation? topic. The fields of view should be less than pi radians.

D3DMATRIX 
ProjectionMatrix(const float near_plane, // Distance to near clipping 
                                         // plane
                 const float far_plane,  // Distance to far clipping 
                                         // plane
                 const float fov_horiz,  // Horizontal field of view 
                                         // angle, in radians
                 const float fov_vert)   // Vertical field of view 
                                         // angle, in radians
{
    float    h, w, Q;
 
    w = (float)1/tan(fov_horiz*0.5);  // 1/tan(x) == cot(x)
    h = (float)1/tan(fov_vert*0.5);   // 1/tan(x) == cot(x)
    Q = far_plane/(far_plane - near_plane);
 
    D3DMATRIX ret;
    ZeroMemory(&ret, sizeof(ret));

    ret(0, 0) = w;
    ret(1, 1) = h;
    ret(2, 2) = Q;
    ret(3, 2) = -Q*near_plane;
    ret(2, 3) = 1;
    return ret;
}   // End of ProjectionMatrix

After you create the matrix, you must set it in a call to the IDirect3DDevice8::SetTransform method, specifying D3DTRANSFORMSTATE_PROJECTION in the first parameter. For details, see Setting Transformations.

The Direct3DX utility library provides the following functions to help you set up your projections matrix:

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Setting Up a Projection Matrix

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