c++ - glm returning nan on simple translate

Question

I'm tinkering with OpenGL using glfw, glad, and glm. In one of the tutorials I'm using, they demonstrate some simple usage of glm as so:

glm::vec4 vec(1.0f, 0.0f, 0.0f, 1.0f);
glm::mat4 trans;
trans = glm::translate(trans, glm::vec3(1.0f, 1.0f, 0.0f));
vec = trans * vec;
std::cout << vec.x << vec.y << vec.z << std::endl;

When I compile and run this code, I get trash values (usually NAN). The tutorial specifically noted that instantiating

glm::mat4 trans;

would by default create an identity matrix for the varialbe "trans". I'm thinking that perhaps this is the issue, though I have verified that glm does do this by default.

In case it would be helpful, you can find the entire source file here on line 308. I greatly appreciate your time!

Answer 1

You have to initialize the matrix variable glm::mat4 trans.

The glm API documentation refers to The OpenGL Shading Language specification 4.20.

5.4.2 Vector and Matrix Constructors

If there is a single scalar parameter to a vector constructor, it is used to initialize all components of the constructed vector to that scalar’s value. If there is a single scalar parameter to a matrix constructor, it is used to initialize all the components on the matrix’s diagonal, with the remaining components initialized to 0.0.

This means, that an identity matrix can be initialized by the single parameter 1.0: glm::mat4(1.0f).

Change your code somehow like this:

glm::mat4 trans(1.0f);

See also OpenGL Mathematics (GLM); 2. Vector and Matrix Constructors