Flags with Repeats

<div style='background:silver;padding:5px'>
<canvas id='usr' width=--snippet-w-- height=--snippet-h--></canvas>
<canvas id='ans' width=--snippet-w-- height=--snippet-h-- style='display:none'></canvas>
</div>

--snippet-usr--
drawFlag(document.getElementById('usr').getContext('2d'));
(()=>{
  --snippet-ans--
  drawFlag(document.getElementById('ans').getContext('2d'));
})();
let [a,b] = ['usr','ans']
    .map(id=>document.getElementById(id))
    .map(elem=>elem.getContext('2d').getImageData(0,0,elem.width,elem.height))
let diff = a.data.map((v,i) => v===b.data[i]?1:0).reduce((acc,v)=>acc+v,0)*100/a.data.length;
let fb = document.createElement('div');
fb.innerText = `Score: ${diff.toFixed(1)}`;
document.body.appendChild(fb);
fetch(`/reportProgress.php?uid=--snippet-uid--&qid=--snippet-qid--&score=${diff}`);

We can repeat a statement or block of statements with a for loop. The classic for loop takes the following form:

for(let i = 0; i< 10; i++){
   console.log(i);
}

The body of the loop runs 10 times, control variable i takes every value 0,1,2..9 in turn. We can use the value of i inside the loop if required.

Bahrain

The flag of Bahrain has a five irregular pentagons on a red background.

Each pentagon can be represented by five points such as (0,0), (64,0) (100,15) (64,31) and (0,31).

Flag of Bahrain

function drawFlag(ctx)
{
  ctx.fillStyle = 'red';
  ctx.fillRect(0,0,250,155);
  for(let i=0;i<3;i++){
    ctx.fillStyle='white';
    ctx.beginPath();
    ctx.moveTo(0,0);
    ctx.lineTo(64,0);
    ctx.lineTo(100,15);
    ctx.lineTo(64,31);
    ctx.lineTo(0,31);
    ctx.fill();
    ctx.translate(0,31);
  }
}

function drawFlag(ctx)
{
  ctx.fillStyle = 'red';
  ctx.fillRect(0,0,250,155);
  for(let i=0;i<5;i++){
    ctx.fillStyle='white';
    ctx.beginPath();
    ctx.moveTo(0,0);
    ctx.lineTo(64,0);
    ctx.lineTo(100,15);
    ctx.lineTo(64,31);
    ctx.lineTo(0,31);
    ctx.fill();
    ctx.translate(0,31);
  }
}

Qatar

Consider the neighbouring state Qatar.

• 9 pillars, each pillar is 17 pixels below the previous.
• The five coordinates of the top pillar are (0,0) (84,0) (125,9) (84,17), (0,17)
• rgb(128,0,0) is a less jaunty red.

The need for a loop becomes even more obvious for this flag.

Flag of Qatar

function drawFlag(ctx)
{
  ctx.fillStyle = 'rgb(128,0,0)';
  ctx.fillRect(0,0,250,155);
}

function drawFlag(ctx)
{
  ctx.fillStyle = 'rgb(128,0,0)';
  ctx.fillRect(0,0,250,155);
  for(let i=0;i<9;i++){
    ctx.fillStyle='white';
    ctx.beginPath();
    ctx.moveTo(0,0);
    ctx.lineTo(84,0);
    ctx.lineTo(125,9);
    ctx.lineTo(84,17);
    ctx.lineTo(0,17);
    ctx.fill();
    ctx.translate(0,17);
  }
}

India

• The flag of India is 306 by 204
• The orange, white and green stripes are equal sizes.
• The wheel has radius 30.
• The wheel has 24 spokes, the spokes are π/12 radians apart.

Whoever wrote the sample code used copy and paste three times, then got bored and gave up. A better programmer would have used a loop. This is the phrase that gets repeated:

 ctx.moveTo(0,0);
 ctx.lineTo(0,30);
 ctx.rotate(Math.PI/12);

We have not really done India justice here - the actual flag is much more elegant, the spokes taper and the rim includes decoration. Nevertheless - we apologize to the sub-continent and move on.

Flag of India

function drawFlag(ctx)
{
  ctx.fillStyle = 'orange';
  ctx.fillRect(0,0,306,204/3);
  ctx.fillStyle = 'lime';
  ctx.fillRect(0,2*204/3,306,204/3);
  ctx.strokeStyle = 'blue';
  ctx.lineWidth = 1.5;
  ctx.translate(153,102);
  ctx.arc(0,0,30,0,2*Math.PI,true);
  ctx.moveTo(0,0);
  ctx.lineTo(0,30);
  ctx.rotate(Math.PI/12);
  ctx.moveTo(0,0);
  ctx.lineTo(0,30);
  ctx.rotate(Math.PI/12);
  ctx.moveTo(0,0);
  ctx.lineTo(0,30);
  ctx.rotate(Math.PI/12);
  ctx.stroke();
}

function drawFlag(ctx)
{
  ctx.fillStyle = 'orange';
  ctx.fillRect(0,0,306,204/3);
  ctx.fillStyle = 'white';
  ctx.fillRect(0,204/3,306,204/3);
  ctx.fillStyle = 'lime';
  ctx.fillRect(0,2*204/3,306,204/3);
  ctx.strokeStyle = 'blue';
  ctx.lineWidth = 1.5;
  ctx.translate(153,102);
  ctx.arc(0,0,30,0,2*Math.PI,true);
  for(let i=0;i<24;i++){
    ctx.moveTo(0,0);
    ctx.lineTo(0,30);
    ctx.rotate(Math.PI/12);
  }
  ctx.stroke();
}