Flags with Lines

<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}`);

Get on with the programming, don't pause to look at this worked example: Road Sign Square

England

The English flag is the cross of St. George. This is a red cross on a white background .

• The line thickness should be 18.

function drawFlag(ctx)
{
  ctx.fillStyle = 'white';
  ctx.fillRect(0,0,150,90);
  ctx.strokeStyle = 'red';
  ctx.lineWidth = 18;
  ctx.moveTo(0,45);
  ctx.lineTo(150,45);
  ctx.stroke();
}

function drawFlag(ctx)
{
  ctx.fillStyle = 'white';
  ctx.fillRect(0,0,150,90);
  ctx.strokeStyle = 'red';
  ctx.lineWidth = 18;
  ctx.moveTo(0,45);
  ctx.lineTo(150,45);
  ctx.moveTo(75,0);
  ctx.lineTo(75,90);
  ctx.stroke();
}

Scotland

The cross of St. Andrew shows diagonal lines on a blue background.

• Complete the flag by drawing the other diagonal line.
• The white lines should be slightly thicker - try 18.

function drawFlag(ctx)
{
  ctx.fillStyle = 'white';
  ctx.fillRect(0,0,150,90);
  ctx.strokeStyle = 'red';
  ctx.lineWidth = 18;
  ctx.moveTo(0,0);
  ctx.lineTo(150,90);
  ctx.stroke();
}

function drawFlag(ctx)
{
  ctx.fillStyle = 'blue';
  ctx.fillRect(0,0,150,90);
  ctx.strokeStyle = 'white';
  ctx.lineWidth = 18;
  ctx.moveTo(0,0);
  ctx.lineTo(150,90);
  ctx.moveTo(0,90);
  ctx.lineTo(150,0);
  ctx.stroke();
}

Botswana

The flag of Botswana has a black stripe on a white stripe on a blue background.

• The flag is 150 by 100
• The white stripe behind the black one has width 30
• The black stripe has width 20
• The pale blue has rgb: '#6EB6ED'

function drawFlag(ctx)
{
  ctx.fillStyle = '#6EB6ED';
  ctx.fillRect(0,0,150,100);
}

function drawFlag(ctx)
{
  ctx.fillStyle = '#6EB6ED';
  ctx.fillRect(0,0,150,100);
  ctx.strokeStyle = 'white';
  ctx.lineWidth = 30;
  ctx.moveTo(0,45);
  ctx.lineTo(150,45);
  ctx.stroke();
  ctx.strokeStyle = 'black';
  ctx.lineWidth = 20;
  ctx.moveTo(0,45);
  ctx.lineTo(150,45);
  ctx.stroke();
}

Iceland

• 125 by 90
• The white cross is 20 wide
• The red cross is 10 wide
• The cross line intersect at (45, 45)

function drawFlag(ctx)
{
}

function drawFlag(ctx)
{
  ctx.fillStyle = 'blue';
  ctx.fillRect(0,0,125,90);
  ctx.strokeStyle = 'white';
  ctx.lineWidth = 20;
  ctx.moveTo(45,0);
  ctx.lineTo(45,90);
  ctx.moveTo(0,45);
  ctx.lineTo(125,45);
  ctx.stroke();
  ctx.strokeStyle = 'red';
  ctx.lineWidth = 10;
  ctx.moveTo(45,0);
  ctx.lineTo(45,90);
  ctx.moveTo(0,45);
  ctx.lineTo(125,45);
  ctx.stroke();
}

Trinidad and Tobago

We can start and end lines outside the confines of the surface.

• The white line has width 35
• The black line has width 25

function drawFlag(ctx)
{
  ctx.fillStyle = 'red';
  ctx.fillRect(0,0,150,100);
  ctx.lineWidth = 35;
  ctx.strokeStyle = 'white';
  ctx.moveTo(0,-25);
  ctx.lineTo(75,50);
  ctx.stroke();
}

function drawFlag(ctx)
{
  ctx.fillStyle = 'red';
  ctx.fillRect(0,0,150,100);
  ctx.lineWidth = 35;
  ctx.strokeStyle = 'white';
  ctx.moveTo(0,-25);
  ctx.lineTo(150,125);
  ctx.stroke();
  ctx.lineWidth = 25;
  ctx.strokeStyle = 'black';
  ctx.moveTo(0,-25);
  ctx.lineTo(150,125);
  ctx.stroke();
}