Deixando aqui meu código, bastante diferente da solução mostrada pelo professor, mas que funciona igualmente bem, espero poder ajudar alguém! :)
<!DOCTYPE html>
<html lang="pt-br">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Bandeiras</title>
</head>
<body>
<canvas width="600" height="400"></canvas>
<script>
var screen = document.querySelector("canvas");
var brush = screen.getContext("2d");
function brazilianFlag() {
brush.fillStyle = "green";
brush.fillRect(0, 0, 600, 400);
brush.fillStyle = "yellow";
brush.beginPath();
brush.moveTo(300, 50);
brush.lineTo(50, 200);
brush.lineTo(550, 200);
brush.fill();
brush.beginPath();
brush.moveTo(50, 200);
brush.lineTo(300, 350);
brush.lineTo(550, 200);
brush.fill();
brush.fillStyle = "darkblue";
brush.beginPath();
brush.arc(300, 200, 100, 0, 2 * Math.PI);
brush.fill();
}
function germanFlag() {
brush.fillStyle = "black";
brush.fillRect(0, 0, 600, 133);
brush.fillStyle = "red";
brush.fillRect(0, 133, 600, 133);
brush.fillStyle = "yellow";
brush.fillRect(0, 266, 600, 133);
}
var counter = 1;
function changeFlags() {
if (counter == 1) {
germanFlag();
counter++;
} else if (counter == 2) {
brazilianFlag();
counter = 1;
}
}
brazilianFlag();
setInterval(changeFlags, 3000);
</script>
</body>
</html>
