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In this tutorial you will learn how to draw graphics on a web page using the HTML5 canvas element.
What is Canvas?
The HTML5 canvas element can be used to draw graphics on the webpage via JavaScript. The canvas was originally introduced by Apple for the Mac OS dashboard widgets and to power graphics in the Safari web browser. Later it was adopted by the Firefox, Google Chrome and Opera. Now the canvas is a part of the new HTML5 specification for next generation web technologies.
By default the element has 300px of width and 150px of height without any border and content. However, custom width and height can be defined using the CSS height and width property whereas the border can be applied using the CSS border property.
Understanding Canvas Coordinates
The canvas is a two-dimensional rectangular area. The coordinates of the top-left corner of the canvas are (0, 0) which is known as origin, and the coordinates of the bottom-right corner are (canvas width, canvas height). Here's a simple demonstration of canvas default coordinate system.
Html5 Canvas Draw
(0,0)
Tip: Place your mouse pointer within the canvas area demonstrated above and you will get its current coordinates relative to the canvas. The element is supported in all major web browsers such as Chrome, Firefox, Safari, Opera, IE 9 and above.
Drawing Path and Shapes on Canvas
In this section we're going to take a closer look at how to draw basic paths and shapes using the newly introduced HTML5 canvas element and JavaScript.
Here is the base template for drawing paths and shapes onto the 2D HTML5 canvas.
All the lines except those from 7 to 11 are pretty straight forward. The anonymous function attached to the window.onload event will execute when the page load. Once the page is loaded, we can access the canvas element with document.getElementById() method. Later we have defined a 2D canvas context by passing 2d into the getContext() method of the canvas object.
Drawing a Line
The most basic path you can draw on canvas is a straight line. The most essential methods used for this purpose are moveTo(), lineTo() and the stroke().
The moveTo() method defines the position of drawing cursor onto the canvas, whereas the lineTo() method used to define the coordinates of the line's end point, and finally the stroke() method is used to make the line visible. Let's try out an example:
Drawing a Arc
You can create arcs using the arc() Arena blaster mac os. method. The syntax of this method is as follow:
The JavaScript code in the following example will draw an arc on the canvas.
Drawing a Rectangle
You can create rectangle and square shapes using the rect() method. This method requires four parameters x, y position of the rectangle and its width and height.
The basic syntax of the rect() method can be given with:
The following JavaScript code will draw a rectangle shape centered on the canvas.
Drawing a Circle
There is no specific method for creating circle like rectangle's rect() method. However, you can create a fully enclosed arc such as circle using the arc() method.
The syntax for drawing a complete circle using the arc() method can be given with:
The following example will draw a complete circle centered on the canvas.
Applying Styles and Colors on Stroke
The default color of the stroke is black and its thickness is one pixel. But, you can set the color and width of the stoke using the strokeStyle and lineWidth property respectivley.
The following example will draw an orange color line having 5 pixels width.
You can also set the cap style for the lines using the lineCap property. There are three styles available for the line caps — butt, round, and square. Here's an example:
Filling Colors inside Canvas Shapes
Rollaround (itch) mac os. You can also fill color inside the canvas shapes using the fillStyle() method.
The following example will show you how to fill a solid color inside a rectangle shape.
Tip: While styling the shapes on canvas, it is recommended to use the fill() method before the stroke() method in order to render the stroke correctly.
Similarly, you can use the fillStyle() method to fill solid color inside a circle too.
Filling Gradient Colors inside Canvas Shapes
You can also fill gradient color inside the canvas shapes. A gradient is just a smooth visual transition from one color to another. There are two types of gradient available — linear and radial.
The basic syntax for creating a linear gradient can be given with:
The following example uses the createLinearGradient() method to fill a linear gradient color inside a rectangle. Let's try it out to understand how it basically works:
Similarly, you can fill canvas shapes with radial gradient using the createRadialGradient() method. The basic syntax for creating a radial gradient can be given with:
The following example uses the createRadialGradient() method to fill a radial gradient color inside a circle. Let's try it out to understand how it actually works:
Drawing Text on Canvas
You can also draw text onto canvas. These texts can contain any Unicode characters. The following example will draw a simple greeting message 'Hello World!' onto a canvas.
You can additionally set the color and alignment of the text on the canvas, like this:
You can also apply stroke on text using the strokeText() method. This method will color the perimeter of the text instead of filling it. However if you want to set both the fill and stroke on canvas text you can use both the fillText() and the strokeText() methods together.
Tip: While styling the text on canvas, it is recommended to use the fillText() method before the strokeText() method in order to render the stroke correctly.
At a Glance
Expert's Rating
Pros
- Detailed help features
- New import and export formats
- Helpful interface
- Extremely versatile
Cons
- Missing DWG export
- Markups do not translate to Acrobat 7 PDF files
Our Verdict
As an image-editing and illustration program particularly well-suited to technical drawings, ACD Systems' Canvas X is truly desert island software—if you can have only one application, Canvas X can handle every graphical task.
The program allows you to work with both bitmap and vector graphics with the precision of a CAD program and the capabilities of a page-layout application. It also can be used as a presentation tool and Web-page creation software. While its features are not as extensive as dedicated graphic or Web design applications, Canvas X nonetheless excels at all these tasks.
New features benefit workgroups and CAD users
The improvements in Canvas X make it far more useful for engineering and architectural projects than the previous version. ACD Systems has expanded the program's import and export capabilities to include 80 file formats, including DXF and DWG import and DXF export, making Canvas compatible with the most widely used CAD formats, including AutoCAD. I'd like to see the ability to export as DWG as well as DXF.
| Canvas X's Smart Toolbox (left) and Canvas Assistant (right) are valuable interface improvements that make the program easier to use. (Click image to open full screenshot) |
Canvas X now allows you to add annotations, markup notes, and comments to collaborate with other people in your workgroup. Annotation tools include highlight, redlining, and callout tools. However, recipients of your files will need Canvas X to view those comments. It would be nice if the annotations could translate into Acrobat 7 annotations when saving as a PDF file.
Canvas X has a more extensive startup dialog, which gives you easy access to the online technical support and online discussion forums. ACD's technical support resources include a getting started area, tutorials, online knowledge base, and a wonderful '7-Minute Solutions' section where dozens of typical tasks are organized and outlined in quick how-to guides.
The new Canvas Assistant is a more extensive addition to the existing Dynamic Help, and consists of a floating hypertext window with information and links about the tool or process you are working with. It can be turned off if you don't want or need it.
Flexible for both bitmaps and vectors
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For technical illustration, some of Canvas X's strengths over other illustration applications come from the CAD (computer-aided design) world, and include extensive layer capabilities, symbol libraries, dimensioning, and a 64-bit coordinate system. These features give Canvas the precision that technical illustrators need to create scaled and measured drawings.
One of Canvas' best new features is its Sprite Effects, which allow you to apply one or more filters (such as zoom, sharpen, color balance, or transparency) to one portion of an illustration without changing the underlying graphic. These effects work on bitmap images and vector-based drawings, as well as combinations of the two. Sets of Sprite Effects can be turned on or off, reused, and applied to multiple images.
Versatile interface
Canvas X's well-designed interface does a great job of presenting context-sensitive tools and options to prevent your screen from becoming too cluttered. For example, the Properties Bar, located across the top of the workspace underneath the toolbar, automatically displays the controls and properties for the currently selected object. The Smart Toolbox, Canvas' tool palette, ensures that only related tools and tool options for the currently active tool are displayed. Even the program's help is context sensitive.
Html5 Canvas Text
Canvas X also has a GIS version for mapping and a Scientific version for graphic analysis of imagery and data from scientific sources.
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Macworld's buying advice
There are enough new features here for existing Canvas users to easily justify an upgrade. New users who can take advantage of Canvas X's versatility will save hundreds of dollars over buying a suite of products to cover all of Canvas' capabilities. Existing users of dedicated applications, such as Adobe Photoshop or Adobe Illustrator may find Canvas X somewhat lacking in their specific area of use, unless they need the added accuracy and features of Canvas' technical illustration capabilities.
[ Greg Miller holds a Master's degree in architecture and is chief technology officer of RDC Interactive, which specializes in new media for the AEC (Architecture, Engineering, and Construction) and publishing markets. ]
