float ComputeScreenSize( const Vector &vecOrigin, float flRadius, const ScreenSizeComputeInfo_t& info )
{
    // This is sort of faked, but it's faster that way
    // FIXME: Also, there's a much faster way to do this with similar triangles
    // but I want to make sure it exactly matches the current matrices, so
    // for now, I do it this conservative way
    /*
    Vector4D testPoint1, testPoint2;
    VectorMA( vecOrigin, flRadius, info.m_vecViewUp, testPoint1.AsVector3D() );
    VectorMA( vecOrigin, -flRadius, info.m_vecViewUp, testPoint2.AsVector3D() );
    testPoint1.w = testPoint2.w = 1.0f;

    Vector4D clipPos1, clipPos2;
    Vector4DMultiply( info.m_matViewProj, testPoint1, clipPos1 );
    Vector4DMultiply( info.m_matViewProj, testPoint2, clipPos2 );
    if (clipPos1.w >= 0.001f)
    {
        clipPos1.y /= clipPos1.w;
    }
    else
    {
        clipPos1.y *= 1000;
    }
    if (clipPos2.w >= 0.001f)
    {
        clipPos2.y /= clipPos2.w;
    }
    else
    {
        clipPos2.y *= 1000;
    }

    // The divide-by-two here is because y goes from -1 to 1 in projection space
    return info.m_nViewportHeight * fabs( clipPos2.y - clipPos1.y ) * 0.5f;
    */

    // NOTE: Optimized version of the above algorithm, which only uses y and w components of clip
    // Can also optimize based on clipPos = a +/- b * r
    const float *pViewProjY = info.m_matViewProj[1];
    const float *pViewProjW = info.m_matViewProj[3];
    float flODotY       = pViewProjY[0] * vecOrigin.x           + pViewProjY[1] * vecOrigin.y           + pViewProjY[2] * vecOrigin.z           + pViewProjY[3];
    float flViewDotY    = pViewProjY[0] * info.m_vecViewUp.x    + pViewProjY[1] * info.m_vecViewUp.y    + pViewProjY[2] * info.m_vecViewUp.z;
    flViewDotY          *= flRadius;
    float flODotW       = pViewProjW[0] * vecOrigin.x           + pViewProjW[1] * vecOrigin.y           + pViewProjW[2] * vecOrigin.z           + pViewProjW[3];
    float flViewDotW    = pViewProjW[0] * info.m_vecViewUp.x    + pViewProjW[1] * info.m_vecViewUp.y    + pViewProjW[2] * info.m_vecViewUp.z;
    flViewDotW          *= flRadius;
    float y0            = flODotY + flViewDotY;
    float w0            = flODotW + flViewDotW;
    y0                  *= ( w0 >= 0.001f ) ? ( 1.0f / w0 ) : 1000.0f;
    float y1            = flODotY - flViewDotY;
    float w1            = flODotW - flViewDotW;
    y1                  *= ( w1 >= 0.001f ) ? ( 1.0f / w1 ) : 1000.0f;

    // The divide-by-two here is because y goes from -1 to 1 in projection space
    return info.m_nViewportHeight * fabs( y1 - y0 ) * 0.5f;
}