How to initialize a glm::mat4 with an array?

Question

I'm using the OpenGL Mathematics Library (glm.g-truc.net) and want to initialize a glm::mat4 with a float-array.

float aaa[16];
glm::mat4 bbb(aaa);

This doesn't work.

I guess the solution is trivial, but I don't know how to do it. I couldn't find a good documentation about glm. I would appreciate some helpful links.

score 93 · Accepted Answer · edited Aug 03 '20 at 12:06

93

Although there isn't a constructor, GLM includes make_* functions in glm/gtc/type_ptr.hpp:

#include <glm/gtc/type_ptr.hpp>
float aaa[16];
glm::mat4 bbb = glm::make_mat4(aaa);

edited Aug 03 '20 at 12:06

Someone

560
9
21

answered Sep 13 '11 at 20:38

Matthew Marshall

5,793
2
21
14

22

Also don't forget to ensure that the source array is stored **column-wise**, otherwise you will need to add `glm::mat4 bbbT = glm::make_mat4(aaa); glm::mat4 bbb = glm::transpose(bbbT);` – Rian Rizvi Sep 03 '14 at 16:19

score 11 · Answer 2 · answered Jul 15 '13 at 14:31

11

You can also directly copy the memory:

float aaa[16] = {
   1, 2, 3, 4,
   5, 6, 7, 8,
   9, 10, 11, 12,
   13, 14, 15, 16
};
glm::mat4 bbb;

memcpy( glm::value_ptr( bbb ), aaa, sizeof( aaa ) );

answered Jul 15 '13 at 14:31

Anderson Silva

131
1
4

Do I need to type "`std::memcpy()`"? Where is this `memcpy()` function? – Nathan majicvr.com Mar 11 '21 at 01:33

score 5 · Answer 3 · answered Sep 13 '11 at 00:22

You could write an adapter function:

template<typename T>
tvec4<T> tvec4_from_t(const T *arr) {
    return tvec4<T>(arr[0], arr[1], arr[2], arr[3]);
}

template<typename T>
tmat4<T> tmat4_from_t(const T *arr) {
    return tmat4<T>(tvec4_from_t(arr), tvec4_from_t(arr + 4), tvec4_from_t(arr + 8), tvec4_from_t(arr + 12));
}


// later
float aaa[16];
glm::mat4 bbb = tmac4_from_t(aaa);

How to initialize a glm::mat4 with an array?

3 Answers3