HTML5 Canvas

John Samuel
CPE Lyon

Année: 2017-2018
Courriel: john(dot)samuel(at)cpe(dot)fr

Creative Commons License

HTML5 Canvas | John Samuel
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HTML5 Canvas

Objectifs

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HTML5 Canvas

Histoire

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Fonctionnement

<body>
...
 <canvas id="moncanvas" width="300" height="400">
 </canvas>
...
</body>

HTML5 Canvas | John Samuel
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Fonctionnement

 <canvas id="moncanvas" width="300" height="400">
 </canvas>

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Fonctionnement

 <canvas id="moncanvas" width="300" height="400">
 </canvas>

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Fonctionnement

<body>
...
 <canvas id="moncanvas" width="300" height="400">
 </canvas>
 <script>
  var id = document.getElementById("moncanvas");
  var context = id.getContext("2d");
 </script>
...
</body>

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Fonctionnement

Dans le body d'un fichier HTML

 <canvas id="moncanvas" width="300" height="400">
 </canvas>

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Fonctionnement

Dans un fichier Javascript ou dans <script>...</script>

 <script>
  var id = document.getElementById("moncanvas");
  var context = id.getContext("2d");
 </script>
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Fonctionnement

Changer la couleur du fond

  id.style.backgroundColor = "green";

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Fonctionnement

Changer l'hauteur et la largeur d'un canvas

  id.style.width = 500;
  id.style.height = 600;

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Fonctionnement

3D en utilisant le contexte WebGL

<body>
...
 <canvas id="moncanvas3D" width="300" height="400">
 </canvas>
 <script>
  var id = document.getElementById("moncanvas3D");
  var context = id.getContext("webgl");
 </script>
...
</body>
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Ligne

<body>
...
 <canvas id="ligne" width="300" height="400">
 </canvas>
 <script>
  var id = document.getElementById("ligne");
  var context = id.getContext("2d");

  context.strokeStyle = "#00b33c";
  context.lineWidth = 10;
  context.moveTo(0,0);
  context.lineTo(300,400);
  context.stroke();
 </script>
...
</body>
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Ligne

 <canvas id="ligne" width="300" height="400">
 </canvas>
 <script>
  var id = document.getElementById("ligne");
  var context = id.getContext("2d");

  context.strokeStyle = "#00b33c";
  context.lineWidth = 10;
  context.moveTo(0,0);
  context.lineTo(300,400);
 </script>
...
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Ligne

<body>
...
 <canvas id="ligne" width="300" height="400">
 </canvas>
 <script>
  var id = document.getElementById("ligne");
  var context = id.getContext("2d");

  context.strokeStyle = "#00b33c";
  context.lineWidth = 10;
  context.moveTo(300,0);
  context.lineTo(0,400);
  context.stroke();
 </script>
...
</body>
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Ligne

  context.beginPath();
  context.strokeStyle = "#00b33c";
  context.moveTo(0,0);
  context.lineTo(300,400);
  context.stroke();
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Lignes

  context.beginPath();
  context.strokeStyle = "#00b33c";
  context.moveTo(0,0);
  context.lineTo(300,400);

  context.strokeStyle = "red";
  context.moveTo(0,400);
  context.lineTo(300,0);
  context.stroke();
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Lignes

  context.beginPath();
  context.strokeStyle = "#00b33c";
  context.moveTo(0,0);
  context.lineTo(300,400);
  context.stroke();

  context.beginPath();
  context.strokeStyle = "red";
  context.moveTo(0,400);
  context.lineTo(300,0);
  context.stroke();
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Arc

  context.beginPath();
  context.arc(200, 150, 100, Math.PI, 1.5 * Math.PI);
  context.stroke();
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Arc

  context.beginPath();
  context.arc(200, 150, 100, Math.PI, 1.5 * Math.PI, true);
  context.stroke();
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Arc

  context.beginPath();
  context.arc(x, y, rayon, angleInitial, angleFinal, antihoraire);
  context.stroke();

Note: Les angles dans la fonction arc sont mesurés en radians.
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Arc

  context.beginPath();
  context.moveTo(0,70);
  context.lineTo(140,70);
  context.arcTo(200, 70, 200, 270, 50);
  context.lineTo(200, 270);
  context.stroke();
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Arc

  context.beginPath();
  context.fillStyle = "#00b33c";
  context.moveTo(0,70);
  context.lineTo(140,70);
  context.arcTo(200, 70, 200, 270, 50);
  context.lineTo(200, 270);
  context.fill();
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Arc

  context.beginPath();
  context.arcTo(x1, y1, x2, y2, rayon);
  context.stroke();
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Courbe

Courbe de Bézier quadratique

  context.beginPath();
  quadraticCurveTo(cp1x, cp1y, x, y);
  context.stroke();
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Courbe

  context.beginPath();
  context.moveTo(0,70);
  context.lineTo(120,70);
  context.quadraticCurveTo(280, 120, 200, 270);
  context.stroke();
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Courbe

Courbe de Bézier cubique

  context.beginPath();
  bezierCurveTo(cp1x, cp1y, cp2x, cp2y, x, y);
  context.stroke();
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Courbe

  context.beginPath();
  context.moveTo(0,70);
  context.lineTo(120,70);
  context.bezierCurveTo(280, 120, 240, 220, 150, 270);
  context.stroke();
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Cercle

  context.beginPath();
  context.arc(150, 150, 100, 0, 2 * Math.PI);
  context.stroke();
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Rectangle

  context.lineWidth = 10;
  context.rect(10, 10, 280, 280);
  context.stroke();
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Rectangle

  context.strokeStyle = "#00b33c";
  context.rect(x, y, largeur, hauteur);
  context.stroke();
  context.strokeStyle = "#00b33c";
  context.strokeRect(x, y, largeur, hauteur);
  context.fillStyle = "#00b33c";
  context.fillRect(x, y, largeur, hauteur);
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Rectangle

  context.fillStyle = "#00b33c";
  context.fillRect(10, 10, 280, 280);
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Polygone

  context.beginPath();
  context.strokeStyle = "#00b33c";
  context.moveTo(10, 10);
  context.lineTo(150, 380);
  context.lineTo(280, 10);
  context.closePath();
  context.stroke();
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Polygone

  context.beginPath();
  context.fillStyle = "#00b33c";
  context.moveTo(10, 10);
  context.lineTo(150, 380);
  context.lineTo(280, 10);
  context.closePath();
  context.fill();
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Polygone

  context.beginPath();
  context.strokeStyle = "#00b33c";
  context.moveTo(10, 200);
  context.lineTo(80, 10);
  context.lineTo(200, 10);
  context.lineTo(270, 200);
  context.lineTo(200, 380);
  context.lineTo(80, 380);
  context.closePath();
  context.stroke();
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Polygone

  context.beginPath();
  context.fillStyle = "#00b33c";
  context.moveTo(10, 200);
  context.lineTo(80, 10);
  context.lineTo(200, 10);
  context.lineTo(270, 200);
  context.lineTo(200, 380);
  context.lineTo(80, 380);
  context.lineTo(80, 380);
  context.closePath();
  context.fill();

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Effacer une zone

  context.clearRect(90, 140, 100, 100);

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Texte

  context.font = "40px Arial";
  context.strokeText("Bonjour!", 100, 100);
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Texte

  context.font = "40px Arial";
  context.fillText("Bonjour!", 100, 100);
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Texte

  context.font = "40px Arial";
  context.strokeText("Bonjour!", 100, 100);
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L'alignement du texte

context.font = "30px Arial";
context.textAlign = "start";
context.fillText("début", 250, 20);

context.textAlign = "end";
context.fillText("fin1 fin2 fin3 fin4 fin5 fin6", 250, 100);

context.textAlign = "left";
context.fillText("gauche1 gauche2 gauche3 gauche4", 250, 180);

context.textAlign = "right";
context.fillText("droite1 droite2 droite3 droite4", 250, 260);

context.textAlign = "center";
context.fillText("centre", 250, 340);

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L'alignement de base

context.font = "20px Arial";
context.textBaseline = "top";
context.fillText("haut", 0, 200);

context.textBaseline = "middle";
context.fillText("moyen", 150, 200);

context.textBaseline = "alphabetic";
context.fillText("alphabetique", 250, 200);

context.textBaseline = "bottom";
context.fillText("en bas", 420, 200);
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Images

 var img = new Image();
 img.src = "img.png";
 img.onload = function() {
  context.drawImage(img, 0, 0);
}
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Images: Mise à l'échelle

 var img = new Image();
 img.src = "img.png";
 img.onload = function() {
  context.drawImage(img, 0, 0, 500, 400);
}
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Images

  void context.drawImage(image, dx, dy);
  void context.drawImage(image, dx, dy, dLargeur, dHauteur);
  void context.drawImage(image, sx, sy, sLargeur, sHauteur, dx, dy, dLargeur, dHauteur);
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Images: Mise à l'échelle

 var img = new Image();
 img.src = "img.png";
 img.onload = function() {
  context.drawImage(img, 0, 0, 250, 200);
  context.drawImage(img, 250, 0, 250, 200);
  context.drawImage(img, 0, 200, 250, 200);
  context.drawImage(img, 250, 200, 250, 200);
}
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Images: Découpage

 var img = new Image();
 img.src = "img.png";
 img.onload = function() {
  context.drawImage(img, 100, 100, 500, 400, 250, 250, 150, 150);
}
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Images: Rotation

 var img = new Image();
 img.src = "img.png";
 img.onload = function() {
  context.rotate(10*Math.PI/180);
  context.drawImage(img, 200, 0, 200, 200);
}
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Images: Mise à l'échelle

 var img = new Image();
 img.src = "img.png";
 img.onload = function() {
  context.scale(0.5, 0.5);
  context.drawImage(img, 200, 0, 200, 200);
}
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Image: Déplacement

 var img = new Image();
 img.src = "img.png";
 img.onload = function() {
  context.drawImage(img, 0, 0, 200, 200);
  context.translate(200, 200);
  context.drawImage(img, 0, 0, 400, 400);
}
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Images: Transformation

 var img = new Image();
 img.src = "img.png";
 img.onload = function() {
  context.drawImage(img, 0, 0, 200, 200);
  context.transform(0.5, 0.5, -0.5, 0.5, 300,10);
  context.drawImage(img, 0, 0, 400, 400);
}
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Interaction: Clavier

 document.onkeydown = function(event) {
  event.preventDefault();

  event = event || window.event;
  if (event.keyCode == '37') {
   // gauche
  }
  else if (event.keyCode == '38') {
   // haut
  }
  else if (event.keyCode == '39') {
   // droite
  }
  else if (event.keyCode == '40') {
   // bas
  }
 }
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Interaction: Souris

 document.getElementById("moncanvas").onmousedown = function(event) {
  event = event || window.event;
  event.preventDefault();

  var posX = event.pageX - canvas.offsetLeft;
  var posY = event.pageY - canvas.offsetTop;
}
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Interaction: Souris

document.body.onmouseup = function(event) {
  event = event || window.event;
  event.preventDefault();
}
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HTML5 Canvas et SVG

SVG Canvas
Pour les images vectorielles Pour les images matricielles
XML Javascript
Manipulation facile des événements du DOM Correspondence des coordonnées du pointeur et d'image
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HTML5 Canvas

Références

Crédits d'images

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