Learn more about Canvas: Uncover its unique features
In-depth understanding of Canvas: revealing its unique features requires specific code examples
With the rapid development of Internet technology, the interface design of applications has become more and more Be diverse and creative. The emergence of HTML5 technology provides developers with more rich tools and functions, of which Canvas is a very important component. Canvas is a new tag in HTML5, which can be used to draw graphics on web pages, create highly interactive animations and games, etc. This article will delve into the unique features of Canvas and give some specific code examples to help readers better understand and use Canvas.
1. The basic composition of Canvas
First of all, we need to understand the basic composition of Canvas. In HTML, we can create a Canvas element through the following code:
<canvas id="myCanvas" width="500" height="500"></canvas>
In the above code, <canvas> is the tag used to define the Canvas element, id# The ## attribute is used to give the Canvas element a unique identity. The width and height attributes define the width and height of the Canvas element respectively. Through this Canvas element, we can draw graphics in it.
- Draw a straight line:
var canvas = document.getElementById("myCanvas");
var ctx = canvas.getContext("2d");
ctx.beginPath();
ctx.moveTo(0, 0);
ctx.lineTo(200, 200);
ctx.strokeStyle = "red";
ctx.lineWidth = 3;
ctx.stroke();getContext() method. Then, use the beginPath() method to start drawing a path, use the moveTo() method to move the stroke to the starting point, and use the lineTo() method to draw a line segment. Finally, define the color and width of the line segment by setting the strokeStyle and lineWidth properties, and finally call the stroke() method to draw the line segment.
- Draw a rectangle:
var canvas = document.getElementById("myCanvas");
var ctx = canvas.getContext("2d");
ctx.beginPath();
ctx.rect(100, 100, 200, 100);
ctx.fillStyle = "blue";
ctx.fill();rect() method to define the position and size of a rectangle. Next, define the fill color of the rectangle by setting the fillStyle property, and finally call the fill() method to fill the rectangle.
- Drawing a circle:
var canvas = document.getElementById("myCanvas");
var ctx = canvas.getContext("2d");
ctx.beginPath();
ctx.arc(250, 250, 100, 0, 2 * Math.PI);
ctx.fillStyle = "green";
ctx.fill();arc() method to draw a circle, and the parameters are the position of the center of the circle, the radius, and the starting and ending radian. Define the fill color of the circle by setting the fillStyle property, and finally call the fill() method to fill the circle.
var canvas = document.getElementById("myCanvas");
var ctx = canvas.getContext("2d");
canvas.addEventListener("mousemove", function(event) {
var x = event.clientX - canvas.offsetLeft;
var y = event.clientY - canvas.offsetTop;
ctx.clearRect(0, 0, canvas.width, canvas.height);
ctx.beginPath();
ctx.arc(x, y, 10, 0, 2 * Math.PI);
ctx.fillStyle = "red";
ctx.fill();
});In the above code, we also obtain the Canvas element and drawing context. Then, a mousemove event is bound to the Canvas element through the addEventListener() method. When the mouse moves on the Canvas, this event will be triggered and the subsequent callback function will be executed. In the callback function, we obtain the coordinate position of the mouse through the clientX and clientY properties, and subtract the offset of the Canvas element to obtain the coordinate position relative to the Canvas element. Then, use the clearRect() method to clear the previously drawn content, and then draw a new circle, with the center position based on the coordinate position of the mouse. Finally, call the fill() method to fill the circle.
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