Drawing on the Web with Canvas Rendering Context

How would you go about creating a 2D drawing app in the browser?

The html canvas element in combination with the CanvasRenderingContext2D interface provides a simple way to draw graphics on the web.

Note: Two alternative options for drawing on the web are WebGL and SVG.

CanvasRenderingContext2D

The CanvasRenderingContext2D interface provides the 2D rendering context for the drawing surface of a canvas element. It is used to draw shapes, text, images, and other objects on the canvas.

This is raster graphics as opposed to vector graphics which is what SVG uses. Raster graphics are made up of pixels, while vector graphics are made up of paths. Raster does not
scale up and down as well as vector graphics.

Use Cases

Some common use cases for the 2D canvas include:

• Photo editing
• Drawing / sketching apps
• Simple games

Example App

In this example we have a couple of simple requirements:

• User can draw lines on the canvas
• User can set a background
• User can choose background and line colors from an EyeDropper color picker and default provided color pallette
• User can clear the canvas
• User can undo / redo
• User can download the drawing as an image
• User can do all of the above with hotkeys

codesandbox.io

Feature Ideas

You could take this example further by adding more features such as:

Pen customization: a form to allow the user to customize the size and brush stroke of the pen.

Saving image state to a persistent store: the image state is currently stored in component state. You could save the image state to a persistent store such as local storage or a database.

Adding text: add a new action button to allow the user to add text to the canvas. The CanvasRenderingContext2D interface provides
strokeText and fillText methods for drawing text on the canvas.

Adding images: allow the user to upload images to the canvas. The CanvasRenderingContext2D interface provides an drawImage method for drawing images on the canvas. This could really open up many possibilities for the app.

Adding a layer system: allow the user to add multiple layers to the canvas. This would allow the user to draw on different layers and toggle the visibility of each layer. This would be a more complex feature to implement but would provide a lot of flexibility to the user.

Fill area: add a new action button to allow the user to fill an area with a color. The CanvasRenderingContext2D interface provides a fill method for filling an area with the current fill style.

Final Thoughts

Its worth mentioning again that WebGL and SVG are two other interesting options for drawing on the web that are worth looking into.

The MDN docs for the CanvasRenderingContext2D interface are a great resource for learning more about the 2D canvas.

Take this example and run with it! There are so many possibilities for creating interesting and interactive drawing apps on the web.

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