C gl-matrix, how to create vectors and matrices? - c

Question

It's code from vec3.c in gl-matrix.
vec3_t vec3_create(vec3_t vec) {
vec3_t dest = calloc(sizeof(double_t), 3);
if (vec) {
dest[0] = vec[0];
dest[1] = vec[1];
dest[2] = vec[2];
} else {
dest[0] = dest[1] = dest[2] = 0;
}
return dest;
}
How can I crate new vector using that function?
How to create vector with different values?
I was trying to set double values to array like this:
vec3_t vec;
vec3_t vec3_create(vec);
vec[0] = 1.0;
vec[1] = 0.0;
vec[2] = 0.0;
But I get EXC_BAD_ACCESS. Have the same problem with matrices.
Code in mat4.c in gl-matrix.
mat4_t mat4_create(mat4_t mat) {
mat4_t dest = calloc(sizeof(double), 16);
if (mat) {
dest[0] = mat[0];
dest[1] = mat[1];
dest[2] = mat[2];
dest[3] = mat[3];
dest[4] = mat[4];
dest[5] = mat[5];
dest[6] = mat[6];
dest[7] = mat[7];
dest[8] = mat[8];
dest[9] = mat[9];
dest[10] = mat[10];
dest[11] = mat[11];
dest[12] = mat[12];
dest[13] = mat[13];
dest[14] = mat[14];
dest[15] = mat[15];
}
return dest;
}
EXC_BAD_ACCESS.
mat4_t transform_mat;
mat4_create(transform_mat);

Answer 1

vec3_t is a pointer to a double as defined in the header
typedef double *vec3_t;
From the header you find also some documentation, which will tell you how to use it:
/*
* vec3_t - 3 Dimensional Vector
*/
/*
* vec3_create
* Creates a new instance of a vec3_t
*
* Params:
* vec - Optional, vec3_t containing values to initialize with. If NULL, the
* vector will be initialized with zeroes.
*
* Returns:
* New vec3
*/
vec3_t vec3_create(vec3_t vec);
So you would might want to do something like this:
vec3_t vec = vec3_create(NULL); // initially a vector with 0s
vec[0] = 1.0; // set the first element to 1.0
In regard to the matrix:
mat4_t transform_mat = mat4_create(NULL);
This will allocate memory and transform_mat will point to its address. You need to initialize the values yourself, as they are not initialized to 0s by default (as it is done with vec3_t).