Getting ready

Download the latest GLM distribution from http://glm.g-truc.net. Unzip the archive file, and copy the glm directory contained inside to anywhere in your compiler's include path.

How to do it...

Using the GLM libraries is simply a matter of including the core header file (highlighted in the following code snippet) and headers for any extensions. We'll include the matrix transform extension, and the transform2 extension.

#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtx/transform2.hpp>

The GLM classes are then available in the glm namespace. The following is an example of how you might go about making use of some of them.

glm::vec4 position = glm::vec4( 1.0f, 0.0f, 0.0f, 1.0f );

glm::mat4 view = glm::lookAt( glm::vec3(0.0,0.0,5.0),
                              glm::vec3(0.0,0.0,0.0),
                              glm::vec3(0.0,1.0,0.0) );

glm::mat4 model = glm::mat4(1.0f);
model = glm::rotate( model, 90.0f, glm::vec3(0.0f,1.0f,0.0) );

glm::mat4 mv = view * model;

glm::vec4 transformed = mv * position;

How it works...

The GLM library is a header-only library. All of the implementation is included within the header files. It doesn't require separate compilation and you don't need to link your program to it. Just placing the header files in your include path is all that's required!

The preceding example first creates a vec4 (four coordinate vector) representing a position. Then it creates a 4x4 view matrix by using the glm::lookAt function from the transform2 extension. This works in a similar fashion to the old gluLookAt function. In this example, we set the camera's location at (0,0,5), looking towards the origin, with the "up" direction in the direction of the Y-axis. We then go on to create the modeling matrix by first storing the identity matrix in the variable model (via the constructor: glm::mat4(1.0f)), and multiplying by a rotation matrix using the glm::rotate function. The multiplication here is implicitly done by the glm::rotate function. It multiplies its first parameter by the rotation matrix that is generated by the function. The second parameter is the angle of rotation (in degrees), and the third parameter is the axis of rotation. The net result is a rotation matrix of 90 degrees around the Y-axis.

Finally, we create our model view matrix (mv) by multiplying the view and model variables, and then using the combined matrix to transform the position. Note that the multiplication operator has been overloaded to behave in the expected way.

As stated above, the GLM library conforms as closely as possible to the GLSL specification, with additional features that go beyond what you can do in GLSL. If you are familiar with GLSL, GLM should be easy and natural to use.

There's more...

It is not recommended to import all of the GLM namespace using a command like:

using namespace glm;

This will most likely cause a number of namespace clashes. Instead, it is preferable to import symbols one at a time, as needed. For example:

#include <glm/glm.hpp>
using glm::vec3;
using glm::mat4;

#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>

...

glm::mat4 proj = glm::perspective( viewAngle, aspect,
                                  nearDist, farDist );
glUniformMatrix4fv(location, 1, GL_FALSE, &proj[0][0]);

See also

The GLM website http://glm.g-truc.net has additional documentation and examples.