Overview of common attributes of HTML5 canvas tag

The Canvas tag is an important element in HTML5, which provides a means to draw graphics through JavaScript. In this article, we will introduce you to the commonly used properties of the Canvas tag and demonstrate their usage through specific code examples.

1. List of common properties

1. width: Set the width of the Canvas. The width can be set using specific pixel values ​​or using relative units such as percentages.
2. height: Set the height of Canvas. Height can also be set using pixel values ​​or relative units.
3. id: Specify a unique ID for the Canvas tag so that it can be manipulated through JavaScript.
4. class: Specify a class name for the Canvas tag to facilitate style control.
5. style: used to set the style of the Canvas label, including background color, border style, etc.
6. getContext(): This is a very important method used to obtain the context of the Canvas object. Drawing, setting styles, and other operations can be performed through context.

The following is a code example for a basic Canvas tag:

<canvas id="myCanvas" width="500" height="300" style="border:1px solid black;"></canvas>

In this example, we create a Canvas tag with a width of 500 pixels and a height of 300 pixels, and A black border is set.

2. Draw graphics

The power of the Canvas tag is that you can use JavaScript code to draw various graphics. Here are some common drawing methods:

1. Draw a straight line: Use the context.lineTo() method to draw a straight line. The following example code draws a straight line from coordinates (50, 50) to coordinates (200, 200).

var canvas = document.getElementById("myCanvas");
var ctx = canvas.getContext("2d");
ctx.beginPath();
ctx.moveTo(50, 50);
ctx.lineTo(200, 200);
ctx.stroke();

2. Draw a rectangle: Use the context.fillRect() method to draw a rectangle. The example code below draws a red rectangle with a width of 100 pixels and a height of 50 pixels.

var canvas = document.getElementById("myCanvas");
var ctx = canvas.getContext("2d");
ctx.fillStyle = "red";
ctx.fillRect(50, 50, 100, 50);

3. Draw a circle: Use the context.arc() method to draw a circle. The example code below draws a blue circle with a radius of 30 pixels.

var canvas = document.getElementById("myCanvas");
var ctx = canvas.getContext("2d");
ctx.beginPath();
ctx.arc(100, 100, 30, 0, 2 * Math.PI);
ctx.fillStyle = "blue";
ctx.fill();

4. Clear the canvas: Use the context.clearRect() method to clear the canvas and achieve dynamic drawing effects. The following example code clears the canvas every second and draws a circle in a random position and color.

var canvas = document.getElementById("myCanvas");
var ctx = canvas.getContext("2d");

function drawCircle() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  var x = Math.random() * canvas.width;
  var y = Math.random() * canvas.height;
  var color = "#"+((1<<24)*Math.random()|0).toString(16);
  ctx.beginPath();
  ctx.arc(x, y, 30, 0, 2 * Math.PI);
  ctx.fillStyle = color;
  ctx.fill();
}

setInterval(drawCircle, 1000);

The above sample code uses the setInterval() function to call the drawCircle() function every second to continuously clear the canvas and draw new circular effect.

Through the above sample code, we can see the usage of some common properties of the Canvas tag and how to use JavaScript to draw graphics. I hope this article will help you understand the use of Canvas tags.

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