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How to Draw a Circle in HTML5 Using Canvas Tag?

in HTML on October 25, 2019

This article uses <canvas> tag in HTML5. Learn the basic in the previous article by clicking Canvas Drawing in HTML5.

I have another post on how to draw a line using canvas tag.

Just the way we drew a line, we can draw a circle on a canvas. To draw a circle we need methods from start point to finish the drawing. It’s a simple method to remember actually and that is beginPath() and just like you have guessed it form it’s name, it begins the path or the drawing start point.

Then just like we use in math, a circle requires radius and the x and y axis. Same way we will use the method arc() to create the curve or arc and pass some more values to create a whole circle.

For example: 

canvasObject.arc(70, 70, 60, 0, 2 * Math.PI);

In the example above, the first two values are for x and y axis. The value 60 is for the radius or in other words, how big you want the circle to be. If you want larger circle, increase that number. 

If you want to write down a syntax, it would be like this:

arc(x-axis,y-axis,radius,starting angle,ending angle)

Make sure to use the x and y axis values lower than the radius or your circle will end up outside your canvas.

We are using arc() method to draw a circle so we need to set the angles in the equation exactly 0 and 2*Math.PI. If you try to set the first value to any other number, it won’t draw a full circle but it will draw an arc of that angle. Similarly, for the 2nd angle, if we try to change value to 1*Math.PI then it won’t fully finish the circle either.

The PI property of Math object returns 3.14 which is the ratio of a circle’s area to the square of its radius.


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