canvas.setAlpha(value)
Set the transparency level with which subsequent draw operations should be performed. The default value for alpha is 255 (fully opaque).
Parameters:
value An integer value from 0 (transparent) to 255 (opaque). Values outside this range will be clamped.
Example:
// Draw three colored bars with different opacities across the canvas on
// an orange background
function fillRGB(name) {
var canvas = sb.getCanvas(name);
var rw = canvas.width / 3;
canvas.fill(0xff8000);
canvas.setAlpha(50);
canvas.fillRect(0, 0, rw, canvas.height, 0xff0000);
canvas.setAlpha(150);
canvas.fillRect(rw, 0, 2*rw, cavas.height, 0x00ff00);
canvas.setAlpha(255);
canvas.fillRect(2*rw, 0, 3*rw, canvas.height, 0x0000ff);
}