var m_app       = require("app");
var m_data      = require("data");

var m_tex         = require("textures");
var m_scenes  = require("scenes");
...

function load_cb(data_id) {
    m_app.enable_camera_controls();

    // place your code here

    var plane = m_scenes.get_object_by_name("Plane");
    var ctx_image = m_tex.get_canvas_ctx(plane, "test_text");

    if (ctx_image) {
		ctx_image.fillStyle = "rgba(255,0,0,255)";
		ctx_image.font = "80px Arial";
		ctx_image.fillText("Hello, World!", 10, 100);
		m_tex.update_canvas_ctx(plane, "test_text");
    }
}