This is the code obtained from an ECS example by Austin Morlan.

class Mat44
{
public:
    Mat44()
    {
        //@formatter:off
        m[0][0] = 1.0f; m[0][1] = 0.0f; m[0][2] = 0.0f; m[0][3] = 0.0f;
        m[1][0] = 0.0f; m[1][1] = 1.0f; m[1][2] = 0.0f; m[1][3] = 0.0f;
        m[2][0] = 0.0f; m[2][1] = 0.0f; m[2][2] = 1.0f; m[2][3] = 0.0f;
        m[3][0] = 0.0f; m[3][1] = 0.0f; m[3][2] = 0.0f; m[3][3] = 1.0f;
        //@formatter:on
    }


    Mat44 operator*(Mat44 const& rhs)
    {
        Mat44 result;

        for (int row = 0; row < 4; ++row)
        {
            for (int col = 0; col < 4; ++col)
            {
                float sum = 0.0f;

                for (int i = 0; i < 4; ++i)
                {
                    sum += m[row][i] * rhs.m[i][col];
                }

                result.m[row][col] = sum;
            }
        }

        return result;
    }


    Vec4 operator*(Vec4 const& rhs)
    {
        return Vec4(
            (rhs.x * m[0][0]) + (rhs.y * m[0][1]) + (rhs.z * m[0][2]) + (rhs.w * m[0][3]),
            (rhs.x * m[1][0]) + (rhs.y * m[1][1]) + (rhs.z * m[1][2]) + (rhs.w * m[1][3]),
            (rhs.x * m[2][0]) + (rhs.y * m[2][1]) + (rhs.z * m[2][2]) + (rhs.w * m[2][3]),
            (rhs.x * m[3][0]) + (rhs.y * m[3][1]) + (rhs.z * m[3][2]) + (rhs.w * m[3][3]));
    }


    float m[4][4];
};

The questions:

1. Please explain to me in simple terms what’s happening in the for loops? (my understanding: for every row, the columns are fully traversed, a variable sum is declared to store the result of the multiplication, then an index(tracker for the multidimensional array)is set to keep track of every index traversed, essentially a sort of “helper” here. If I’m correct so far, I can’t build on from here, perhaps there’s a better way to help me understand what’s happening here?

2. Are these the abstractions hidden by the GLM library?

3. My CPP knowledge is intermediate, I can’t understand why the operator overload takes a parameter

4. And finally, for the Vec4 class, I don’t even know what’s going on?