Here is how I set my camera:
camera = camera_create();
var _vm = matrix_build_lookat(x,y,-100,x,y,0,0,1,0);
var _pm = matrix_build_projection_ortho(cam_xdim, cam_ydim, 1.0, 32000.0);
camera_set_view_mat(camera, _vm);
camera_set_proj_mat(camera, _pm)...