glm::vec3 和 glm::mat4 是如何初始化的？

Question

This is about understanding the glm source. I wanted to know if glm does zero initialise its classes and tried it. Yes, glm::vec3 and glm::mat4 are initialized, even without providing a constructor value. Then I wanted to understand how it is done and read the source of glm::mat4 template.

There is this section:

...
enum ctor{null};

// Constructors
GLM_FUNC_DECL tmat4x4();
GLM_FUNC_DECL tmat4x4(tmat4x4 const & m);
GLM_FUNC_DECL explicit tmat4x4(ctor Null);
...

I can read there is a (void) constructor (ctor) but without definition, so no {...} section. And there is an explicit ctor with 0 as parameter coming from first element of type enum ctor , which of course gets index value 0 .

• Where are the constructor definitions? How can I find them?
• What is that explicit Null ctor for?
• How is glm::mat4 initialised to an identity matrix when I just write: glm::mat4 myMatrix;

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Edit: browsing the more current source files on GitHub brings one from mat4x4.hpp to detail/type_mat4x4.hpp which #includes the implementation details in type_mat4x4.inl . There the ctor behaviour gets visible.

Answer 1

It's not inialized by default anymore. Define GLM_FORCE_CTOR_INIT before your includes to force the initialization. https://github.com/g-truc/glm/issues/809

#define GLM_FORCE_CTOR_INIT
#include <glm/glm.hpp>

Answer 2

• it's under "glm/detail/type_mat4x4.inl"
• it's a constructor that does nothing, in 0.9.6.3 it becomes enum ctor{uninitialize}
• It calls the default constructor

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BTW, I can't download your version, this answer is base on 0.9.6.3

Answer 3

glm::mat4x4 view{ 2 / (right - left), 0, 0, 0,
            0, 2 / (top - bottom), 0, 0,
            0, 0, -2 / (farplane - nearplane), 0,
            -((right + left) / (right - left)), -((top + bottom) / (top - bottom)), -((farplane + nearplane) / (farplane - nearplane)), 1
        };


glm::mat4 view{ 2 / (right - left), 0, 0, 0,
            0, 2 / (top - bottom), 0, 0,
            0, 0, -2 / (farplane - nearplane), 0,
            -((right + left) / (right - left)), -((top + bottom) / (top - bottom)), -((farplane + nearplane) / (farplane - nearplane)), 1
        };

glm::uvec4 ViewPort(0,0,0,0);

glm::vec3 Origin(0.0f, 0.0f, 0.0f);