# Drawing Basic Shapes with HTML5 Canvas

### HTML5 Canvas lets us draw basic shapes. Discover how drawing works and how to make basic shapes with HTML Canvas.

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Join For FreeSince HTML5 Canvas is a graphic tool, it goes without saying that it allows us to draw shapes. We can draw new shapes using a number of different functions available to use via the context we set.

In this guide, we'll cover how to make some of the most basic shapes with HTML5 Canvas — squares, rectangles, circles, and triangles.

## Creating Rectangles and Squares with HTML5 Canvas

Squares and rectangles are easy to make in HTML5 Canvas. There are a number of different `rect`

functions we can use to make shapes.

`rect(x, y, width, height)`

— outlines where a rectangle or square should be, but does not fill it.`fillRect(x, y, width, height)`

— creates a rectangle and immediately fills it.`strokeRect(x, y, width, height)`

— creates a rectangle and immediately outlines it with a stroke.

As you can see, all of these functions follow the same format - they have an x- and y-coordinate for where they start, and a width and height within the canvas. Let's look at some examples in code.

### Clear Rectangle Function

#### Using `rect()`

to Create a Rectangle

If we want to use `rect()`

to create a rectangle, and then fill and stroke it, we need to define the fillStyle and strokeStyle. For example, the below code will create a rectangle starting at (10, 10), of dimensions 100x150, with a #b668ff background, and 5px wide white stroke:

```
let canvas = document.getElementById('canvas');
let ctx = canvas.getContext('2d');
ctx.rect(10, 10, 100, 150);
ctx.fillStyle = '#b668ff';
ctx.strokeStyle = 'white';
ctx.lineWidth = 5;
ctx.fill();
ctx.stroke();
```

#### Using fillRect() to Create a Rectangle

fillRect lets us create a rectangle and automatically fill it with a specific color. That means we don't have to use fill() separately.

For example, the following will fill a rectangle of the same size as before, with a #b668ff background:

```
let canvas = document.getElementById('canvas');
let ctx = canvas.getContext('2d');
ctx.fillStyle = '#b668ff';
ctx.fillRect(10, 10, 100, 150);
```

#### Using strokeRect() to create a rectangle

strokeRect() follows a similar format, only it will create a rectangle that is stroked automatically. For example, the below code will make a rectangle of the same dimensions and position as before, with a 5px wide #b668ff border/stroke:

```
let canvas = document.getElementById('canvas');
let ctx = canvas.getContext('2d');
ctx.strokeStyle = '#b668ff';
ctx.lineWidth = 5;
ctx.strokeRect(10, 10, 100, 150);
```

## Creating Circles in HTML5 Canvas

The easiest way to create a circle in HTML5 Canvas is to use the `arc`

function. An arc doesn't have to draw a full circle, though - it can draw only part of a circle by changing the start and end angles. Let's look at the syntax of ctx.arc, and how to make a circle.

`ctx.arc(x, y, radius, startAngle, endAngle, counterClockwise?)`

`x`

— refers to the x coordinate of the center of the circle.`y`

— refers to the y coordinate of the center of the circle.`radius`

— the radius of the arc we are drawing.`startAngle`

— the angle at which the arc starts (in radians).`endAngle`

— the angle at which the arc ends (in radians).`counterClockwise`

— whether the angle goes counterclockwise (default is false; can be set to true).

If we set our `startAngle`

to `0 Radians`

, it will start at the center-right side of the circle. A circle is `2π radians`

in diameter. If we want to draw a full circle, our startAngle is `0`

, and our endAngle is `2π`

.

We can represent this in code using `Math.PI * 2`

. Here is our code to draw a circle, with a 4px wide stroke in #b668ff, with a radius of `90px`

, where its center point is (100, 100):

```
let canvas = document.getElementById('canvas4');
let ctx = canvas.getContext('2d');
ctx.arc(100, 100, 100, 0, Math.PI * 2, false);
ctx.strokeStyle = '#b668ff';
ctx.lineWidth = 4;
ctx.stroke();
```

## Creating Semi-Circles with HTML5 Canvas

Since we can use arc to draw circles and adjust our endAngle, we can also use it to draw a semi-circle. As a full circle is 2π in diameter, a semi-circle is only 1π radians. The only extra step we have to do here is drawing a line from the end of our semi-circle, back to the beginning again.

Since we are going to end at (10, 100) - as our radius is 90px, we draw a line with the lineTo function back to our starting point, which is (190, 100).

```
let canvas = document.getElementById('canvas');
let ctx = canvas.getContext('2d');
ctx.arc(100, 100, 90, 0, Math.PI * 1, false);
ctx.lineTo(190, 100);
ctx.fillStyle = '#b668ff';
ctx.fill();
```

We can flip our semi-circle by changing the counterclockwise option to true:

```
ctx.arc(100, 100, 90, 0, Math.PI * 1, true);
```

## Creating Ovals with HTML Canvas

We can draw an oval in HTML5 canvas by using the ellipse() function. It works in a very similar way to arc(), except we have two radius options.

`ctx.ellipse(x, y, radiusX, radiusY, rotation, startAngle, endAngle, counterClockwise?)`

`x`

- refers to the x coordinate of the center of the circle.`y`

- refers to the y coordinate of the center of the circle.`radiusX`

- the radius along the X axis of the arc we are drawing.`radiusY`

- the radius along the Y axis of the arc we are drawing.`rotation`

- how much we wish to rotate our ellipse shape, in radians.`startAngle`

- the angle at which the arc starts (in radians).`endAngle`

- the angle at which the arc ends (in radians).`counterClockwise`

- whether the angle goes counter clockwise (default is false, can be set to true).

Here is an example, using the same concepts as we did before with `arc()`

:

```
let canvas = document.getElementById('canvas');
let ctx = canvas.getContext('2d');
ctx.ellipse(100, 60, 90, 60, 0, 0, Math.PI * 2, false);
ctx.fillStyle = '#b668ff';
ctx.fill();
```

## Creating Triangle Shapes with HTML Canvas

There is no built-in triangle function in Javascript, so we have to use the lineTo and moveTo function instead. All these functions do are draw lines on the context, to specific points.

We use `moveTo`

to determine the starting position of our triangle, and then draw lines as appropriate to draw the shape of the triangle we want. Here is an example where we draw a triangle and fill it with #b668ff.

```
let canvas = document.getElementById('canvas8');
let ctx = canvas.getContext('2d');
ctx.moveTo(20, 0);
ctx.lineTo(40, 30);
ctx.lineTo(0, 30);
ctx.lineTo(20, 0);
ctx.fillStyle = '#b668ff';
ctx.fill();
```

- We start by using moveTo to determine the starting point of our triangle.
- Then, we draw a line from (20, 0) to (40, 30) - i.e. 20px to the right, and 30px down from our starting point.
- Since this triangle will be symmetrical, we draw a 20px to the left, and 30px down, i.e. (0, 30).
- Finally, we join our shape up by drawing a line back to our starting point, which was (20, 0).
- Then we fill it, and we have a triangle.

The `lineTo()`

function can be used to draw many more complicated shapes in HTML Canvas, which are not built-in by default. Any custom polygons will use `lineTo`

, such as Hexagons, Octagons, or even Parallelograms.

## Conclusion

In this guide, we've covered how to make some simple shapes in HTML canvas: squares, rectangles, circles, and triangles. We've also touched upon the fact that `lineTo`

can be used to draw a line anywhere on our canvas, allowing us to make more complicated shapes like hexagons and octagons. I hope you've enjoyed this article.

Published at DZone with permission of Johnny Simpson, DZone MVB. See the original article here.

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