Tutorial: Transparent Rectangle

/* 
/* Get canvas HTML element */
var canvas = document.getElementById("canvas");

/* Create a Linen instance for the canvas element. */
var Canvas = new Linen(canvas);

/* Draw a rectangle that is centered in the canvas */
Canvas.addElement("Rectangle")
        .setWidth("50%") //width in px, in, pt, or % of canvas width
        .setHeight(300) //height in px, in, pt, or % of canvas height
        .setXY("50%", 350) //x and y position in px, in, pt, or % of canvas width and height, respectively
        .setAlignment("center") //the horizontal point to use for positioning the rectangle (left|center|right)
        .setVAlignment("middle") //the vertical point to use for positioning the rectangle (top|middle|bottom)
        .setFillStyle("rgba(150,10,10, .5)") //the color to fill the rectangle with.
        .setFill(); //tells Linen to fill the rectangle

/* Render the elements above onto the canvas. */
Canvas.render();