To start drawing with HTML5 Canvas, you must first add the canvas element in HTML and get the context with JavaScript; 1. Set the canvas element and specify the width and height; 2. Use JavaScript to get canvas through getElementById and call getContext('2d') to get the drawing context; 3. You can draw rectangles, paths, circles and other figures, such as fillRect filling rectangles, beginPath combined with moveTo/lineTo/closePath to draw polygons, arc drawing circles; 4. Use fill and stroke figures to fill and stroke respectively; 5. Set strokeStyle and lineWidth to control line styles; 6. Beginners should pay attention to calling beginPath to avoid path conflicts, deal with high-resolution display adaptation, and frequently test code. After mastering the basics, you can further realize complex functions such as images and animations.
Drawing with HTML5 Canvas is a powerful way to create graphics directly in the web browser using JavaScript. It's not just for simple shapes — you can make animations, games, data visualizations, and more. If you're looking to get started with drawing on canvas, here's what you need to know.
Setting up the Canvas Element
Before you start drawing, you need to add a <canvas></canvas> element to your HTML file. Think of it like a blank piece of paper that you'll draw on with JavaScript.
<canvas id="myCanvas" width="500" height="500"></canvas>
This creates a canvas area 500 pixels wide and tall. You can adjust these values ??depending on your needs. The next step is to access this canvas from JavaScript:
const canvas = document.getElementById('myCanvas'); const ctx = canvas.getContext('2d');
Now you have a context ( ctx ) which gives you all the drawing tools you'll use.
A few things to keep in mind:
- Always check if the canvas element is properly loaded before accessing it.
- You can style the canvas with CSS, but be careful — scaling via CSS might distort your drawings unless handled correctly.
Basic Shapes: Rectangles and Paths
Once you've set up the canvas, you can start drawing basic shapes. Rectangles are straightforward:
ctx.fillStyle = 'blue'; ctx.fillRect(50, 50, 100, 100);
This draws a blue square at position (50, 50) with a size of 100x100 pixels.
For other shapes like triangles or custom paths, you'll use path-drawing commands:
ctx.beginPath(); ctx.moveTo(100, 100); ctx.lineTo(150, 50); ctx.lineTo(200, 100); ctx.closePath(); ctx.fillStyle = 'red'; ctx.fill();
This draws a red triangle. Breaking it down:
-
beginPath()starts a new shape. -
moveTo()moves the drawing "pen" to a starting point. -
lineTo()draws lines to specified points. -
closePath()connects the last point back to the first. -
fill()fills the shape with color.
You can also use stroke() instead of fill() to only draw the outline.
Drawing Circles and Using Stroke Styles
Circles and arcs are drawn using the arc() method:
ctx.beginPath(); ctx.arc(100, 100, 50, 0, Math.PI * 2); ctx.fillStyle = 'green'; ctx.fill();
This creates a green circle centered at (100, 100) with a radius of 50 pixels.
If you want an outlined circle instead of a filled one, try this:
ctx.strokeStyle = 'black'; ctx.lineWidth = 3; ctx.stroke();
Here's how to control stroke appearance:
- Use
strokeStyleto set the color. - Set
lineWidthto define the thickness. - You can also customize line caps and joins if needed.
Keep in mind that strokes are drawn centered on the path, so half the width appears inside the shape and half outside.
A Few Tips for Beginners
As you start experimenting with canvas drawing:
- Always call
beginPath()before starting a new shape to avoid unexpected behavior. - Save and restore canvas state when rotating or scaling using
ctx.save()andctx.restore(). - Don't forget to handle high-DPI displays by adjusting canvas size based on device pixel ratio if needed.
- Test your code frequently — canvas doesn't show errors visually unless something crashes.
There's more to canvas than just drawing shapes — once you're comfortable with basics, you can move on to images, text, gradients, transformations, and even animation.
Basically that's it.
The above is the detailed content of HTML5 canvas tutorial for drawing. For more information, please follow other related articles on the PHP Chinese website!
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