qt-everywhere-src-5.14.1/qtscript/examples/script/context2d/scripts/rgba.js

var ctx = document.getElementById('tutorial').getContext('2d');

  // Draw background
  ctx.fillStyle = 'rgb(255,221,0)';
  ctx.fillRect(0,0,150,37.5);
  ctx.fillStyle = 'rgb(102,204,0)';
  ctx.fillRect(0,37.5,150,37.5);
  ctx.fillStyle = 'rgb(0,153,255)';
  ctx.fillRect(0,75,150,37.5);
  ctx.fillStyle = 'rgb(255,51,0)';
  ctx.fillRect(0,112.5,150,37.5);

  // Draw semi transparent rectangles
  for (i=0;i<10;i++){
    ctx.fillStyle = 'rgba(255,255,255,'+(i+1)/10+')';
    for (j=0;j<4;j++){
      ctx.fillRect(5+i*14,5+j*37.5,14,27.5)
    }
  }