[训练师杰克儿]

Eigen::Matrix4f get_projection_matrix(float eye_fov, float aspect_ratio, float zNear, float zFar)
{
    // TODO: Copy-paste your implementation from the previous assignment.// 那我就复制了捏Q
    Eigen::Matrix4f projection = Eigen::Matrix4f::Identity();

    Eigen::Matrix4f ortho;// 正交投影矩阵
    Eigen::Matrix4f persp_to_ortho;// 透视投影转正交投影的矩阵
    double fov = eye_fov / 180 * MY_PI;// 转化为弧度制

    double n = -zNear, f = -zFar;

    double top = abs(n) * tan(fov / 2.0f);
    double bottom = -top;
    double right = aspect_ratio * top;
    double left = -right;

    Eigen::Matrix4f ortho_1;// 用于得到正交投影矩阵的被乘矩阵
    Eigen::Matrix4f ortho_2;// 用于得到正交投影矩阵的乘矩阵

    ortho_1 << 2 / (right - left), 0, 0, 0,
        0, 2 / (top - bottom), 0, 0,
        0, 0, 2 / (n - f), 0,
        0, 0, 0, 1;

    ortho_2 << 1, 0, 0, -(right + left) / 2,
        0, 1, 0, -(top + bottom) / 2,
        0, 0, 1, -(n + f) / 2,
        0, 0, 0, 1;

    ortho = ortho_1 * ortho_2;

    persp_to_ortho << n, 0, 0, 0,
        0, n, 0, 0,
        0, 0, n + f, -n * f,
        0, 0, 1, 0;
    
    projection = ortho * persp_to_ortho;

    return projection;
}

闫老师上课过程中所讲到的 zNear 和 zFar 是负数，而代码中的处理是正数。此时在写透视投影的过程中取 n = -zNear 和 f = -zFar，再把代码框架中定义的近平面和远平面（原始代码中仍为正数）改为负数，这样就可以得到正确的图像和覆盖关系。（三角形分开了是我 z-Buffer 写的有问题）

    float f1 = -(50 - 0.1) / 2.0;// 近平面（这里我做下修改 改正负）
    float f2 = -(50 + 0.1) / 2.0;// 远平面（同上）

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