Irrlicht Engine

Posted: **Fri Jul 26, 2024 1:25 pm**

    core::matrix4 A = core::matrix4();

    A[0] = -125;
    A[1] = 25;
    A[2] = -5;
    A[3] = 1;

    A[4] = 0;
    A[5] = 0;
    A[6] = 0;
    A[7] = 1;

    A[8] = 75;
    A[9] = -10;
    A[10] = 1;
    A[11] = 0;

    A[12] = 0;
    A[13] = 0;
    A[14] = 1;
    A[15] = 0;

    core::matrix4 Ai = core::matrix4();

    if (A.getInverse(Ai))
    {
        f32 a[4] = {2, 2, 2, 1};
        Ai.multiplyWith1x4Matrix(a);
        printf("%f\n%f\n%f\n%f\n", a[0], a[1], a[2], a[3]);
    }

Expected output:

Code: Select all

Actual output:

Code: Select all

I've already checked getInverse and it works fine

Posted: **Fri Jul 26, 2024 1:57 pm**

Rows and columns in computer matrices tend to be different than in math (edit: or maybe depends on the library, I think Irrlicht was heavily influenced by Direct3d back then). As computer matrices tend to use row major instead of column major like the math guys. It's kinda meant to transform a 4 element vector by the matrix I guess. Which it does. If you use transposed matrix instead you get your result.

But maybe stupid name - I just realize someone managed to persuade me to add transformVec4 a few years ago because neither of us realized at that point that this function exists already and does the same.

Irrlicht Engine

[no bug]multiplyWith1x4Matrix is really wrong

[no bug]multiplyWith1x4Matrix is really wrong

Re: multiplyWith1x4Matrix is really wrong