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2025-01-24 Update From: SLTechnology News&Howtos shulou NAV: SLTechnology News&Howtos > Development >
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This article mainly shows you "what is the use of HTML5 Canvas API", the content is easy to understand, clear, hope to help you solve your doubts, the following let the editor lead you to study and learn "what is the use of HTML5 Canvas API" this article?
Canvas is a resolution-dependent bitmap canvas on which you can draw arbitrary graphics or even load photos. In HTML5, a series of standard Canvas API is defined for drawing graphics, creating gradients, processing images, and even for pixels.
Here, we would like to raise two questions for members to think about. These are two questions that most beginners and some experienced friends may not be able to answer accurately. Please be sure to think carefully about these two questions, which are the basic issues for becoming a master of Canvas.
Is the question 1:Canvas transparent?
Can question 2:Canvas be stacked on top of each other?
This article is only used as an indexed introduction to Ganvas API. For more information, please see other articles on this site.
Previous similar solutions
In the past, to draw in a browser, we could only use SVG (Scalable Vector Graphics, scalable vector graphics), Flash, or VML (Vector Markup Language, vector markup language) that only supported IE.
These technologies have the following disadvantages.
Plug-ins such as Flash may fail or may be disabled.
Security issues for plug-ins: third-party plug-ins are likely to have security issues that lead to attacks.
The implementation of plug-ins and Web pages is inconsistent, resulting in integration with other Web elements is a big problem.
Advantages of Canvas
When we learn Canvas, we can first understand some of the advantages of Canvas, establish a preliminary impression for readers, and be able to accurately make technical selection when the actual project needs in the future.
Here are the main advantages of Canvas.
has good performance. The mechanism of Canvas determines that there is no need to store every element in the drawing image as an object, and the execution performance is very good.
is powerful. Canvas provides a lot of image processing API, which can easily edit and process pictures and videos.
compatibility is good. Currently, the latest versions of all major browsers support HTML5 Canvas, so there is no need to worry about browser compatibility.
Check whether the browser supports Canvas
In this section, we present two ways to detect whether the browser supports Canvas. We recommend using the second method, which combines the ability of the tag itself to make a concise and effective judgment.
through native JavaScript
The code to detect whether the browser supports Canvas through native JavaScript code is as follows:
If (! document.createElement ('canvas') .getContext) {
/ / if the canvas element cannot be created, execute the code here
}
directly uses the canvas tag to determine
The code to directly use the canvas tag to detect whether the browser supports Canvas is as follows:
Your browser does not support Canvas
If your browser supports Canvas API, the browser will not display the phrase "your browser does not support Canvas"
If your browser does not support Canvas API, the browser will display "your browser does not support Canvas" without interpreting the tag.
Main operation of Canvas
This section gives readers a brief introduction to some of the main operations of Canvas, such as creating Canvas elements, creating a two-dimensional context, setting the size of the Canvas canvas, drawing canvases, and so on.
1. Create a Canvas element
We create the Canvas element in two ways.
is created through HTML. The code in the HTML page is:
After creating through HTML, we use the following method in JavaScript to get this element:
Var canvas = document.getElementById ('mycanvas')
is created directly through JavaScript. The creation code is as follows:
Var canvas = document.createElement ('canvas')
two。 Create a 2D context
With Canvas, you first get its context, and then perform the operation in that context. Currently, the optional context is 2D (3D context is not officially supported by the HTML5 standard). The code is as follows:
Var ctx = canvas.getContext ('2d')
3. Set the Canvas canvas size
The code to set the Canvas canvas size is as follows:
Canvas.width = 600,
Canvas.height = 600,
4. Draw the canvas
Once we have a reference to the context, we can display it on the Canvas using the drawImage () method, which looks like this:
Ctx.drawImage (image, x, y)
Image points to a reference to our image or Canvas object, and x and y refer to the coordinates where the image is placed on the canvas.
5. Simple image processing effect
Here we only briefly introduce three kinds of image processing effects, namely, move, scale, and rotate, which involve the translate (), scale () and rotate () methods.
The translate (XQuery y) method is used to move the origin of the Canvas to another location. It accepts two parameters, where x is the left and right offset and y is the upper and lower offset.
The scale (xQuery y) method is used to reduce or enlarge a shape or image. It accepts two parameters: X and y are the scaling factors of the horizontal and vertical axes, respectively.
The rotate () method is used to rotate the Canvas around the origin, and it accepts only one parameter: the angle of rotation. The value is calculated clockwise and is measured in radians.
The above is all the content of this article "what's the use of HTML5 Canvas API?" Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!
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