This function will set the projection matrix for a given camera. You give the unique camera ID value (as returned by the different camera_create functions) and a view matrix to be applied. You can find out more about creating projection matrices from the section Matrix Functions, specifically matrix_build_projection_perspective and matrix_build_projection_ortho. Note that if your camera does automatic object tracking - ie: it has been created using camera_create_view with an object index / instance ID that isn't -1, or you are setting a camera defined in the Room Editor, or you are setting the default camera - then this matrix will get overwritten the next game frame.
Argument Description camera_id The unique camera ID value returned when you created the camera. matrix The unique matrix ID returned when you created the matrix.
view_camera = camera_create();
var viewmat = matrix_build_lookat(640, 240, -10, 640, 240, 0, 0, 1, 0);
var projmat = matrix_build_projection_ortho(640, 480, 1.0, 32000.0);
The above code creates a new camera and assigns it to view port. This camera then has its view and projection matrices set.