How to draw a circle on an HTML5 canvas?
To draw a circle, use the arc() method; 1. Create a canvas element in HTML; 2. Get the context in JavaScript; 3. Call beginPath() to start the path; 4. Use arc(100, 100, 50, 0, 2 * Math.PI); 5. Use stroke() stroke or fill() to fill(); styles can be set through fillStyle, strokeStyle and lineWidth. BeginPath() should be called before drawing a new shape to avoid path connections, and the coordinates are based on the upper left corner of the canvas.
To draw a circle on an HTML5 canvas, you use the arc() method of the canvas 2D rendering context. Here's how to do it step by step.
Set up the canvas element
First, make sure you have a <canvas></canvas> element in your HTML:
<canvas id="myCanvas" width="200" height="200"></canvas>
Get the 2D context and draw the circle
In JavaScript, get the canvas and its 2D drawing context, then use the arc() method:
const canvas = document.getElementById('myCanvas'); const ctx = canvas.getContext('2d'); // Start drawing the circle ctx.beginPath(); ctx.arc(100, 100, 50, 0, 2 * Math.PI); ctx.stroke(); // or use ctx.fill() to fill the circle
Breakdown of the arc() method
The arc() method takes six parameters:
- x : The x-coordinate of the center (eg, 100)
- y : The y-coordinate of the center (eg, 100)
- radius : The radius of the circle (eg, 50)
- startAngle : Starting angle in radians (0 means 3 o'clock)
- endAngle : Ending angle in radians (
2 * Math.PIcompletes the circle) - counterclockwise : Optional;
truefor counterclockwise,false(default) for clockwise
Customize appearance
You can change the stroke color, line width, or fill the circle:
ctx.beginPath(); ctx.arc(100, 100, 50, 0, 2 * Math.PI); ctx.fillStyle = 'blue'; // Fill color ctx.strokeStyle = 'black'; // Border color ctx.lineWidth = 2; ctx.fill(); // Fills the circle ctx.stroke(); // Draws the border
Tips
- Always call
beginPath()before starting a new shape to avoid connecting to previous paths. - Use
fill()to color the inside,stroke()to draw the outline. - Coordinates are relative to the top-left corner of the canvas.
Basically, arc() is the standard and most accurate way to draw a perfect circle on an HTML5 canvas.
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