The dream of SVG was probably born sometime in the late 90′s. Version 1.0 arrived in 2001, followed by the current version, SVG 1.1, in 2003. For anyone keeping score at home, that’s over 6 years ago, which is like 120 years ago in internet dog years. Also for those at home, SVG is a portable XML-based vector graphics format (it also does raster graphics), but you’d probably not be reading this if you didn’t already know.
Nowadays, I’m finally seeing some SVG in use. It works natively in all the real browsers (obviously not IE, which requires a plugin), and even on some mobile devices. But most importantly to me, I see it in my day-to-day work in Degrafa, and with the beta release of Flex 4, in Catalyst and FXG.
The vast majority of my experience in SVG is with paths (SVG Spec, § 8) and to a lesser extent Transforms (§ 7) and Filters (§ 15). Thankfully, these are some of the most useful and important pieces of SVG, and they all have nice one-to-one mappings to components in Degrafa and FXG.
SVG Path Primer
In SVG, a path is the outline of some object. It is described as a series of segments, where each segment can be different, either a line, curve, or arc. Path data is most often given in shorthand syntax as a series of commands followed by coordinates (we’ll ignore the long form for now). Let’s illuminate the discussion with some examples.
SVG:
<?xml version="1.0" standalone="no"?> <!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd"> <svg xmlns="http://www.w3.org/2000/svg" version="1.1" width="200" height="200"> <path d="M 0,0 L 100,0 L 100,100 L 0,100 z" fill="#EECCEE" stroke="#FF00FF" stroke-width="3" /> </svg>
Degrafa in Flex 3:
<?xml version="1.0" encoding="utf-8"?> <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" xmlns:Degrafa="http://www.degrafa.com/2007" layout="absolute"> <Degrafa:GeometryComposition graphicsTarget="{[cnv]}"> <Degrafa:Path data="M 0,0 L 100,0 L 100,100 L 0,100 z"> <Degrafa:fill> <Degrafa:SolidFill color="#EECCEE" /> </Degrafa:fill> <Degrafa:stroke> <Degrafa:SolidStroke color="#FF00FF" weight="3" /> </Degrafa:stroke> </Degrafa:Path> </Degrafa:GeometryComposition> <mx:Canvas id="cnv" /> </mx:Application>
MXML Graphics (aka FXG) in Flex 4:
<?xml version="1.0" encoding="utf-8"?> <s:Application xmlns:fx="http://ns.adobe.com/mxml/2009" xmlns:s="library://ns.adobe.com/flex/spark" xmlns:mx="library://ns.adobe.com/flex/halo"> <s:Graphic> <s:Path data="M 0,0 L 100,0 L 100,100 L 0,100 z"> <s:fill> <mx:SolidColor color="#EECCEE" /> </s:fill> <s:stroke> <mx:SolidColorStroke color="#FF00FF" weight="3" /> </s:stroke> </s:Path> </s:Graphic> </s:Application>
The examples above use the shorthand path syntax to draw a 100px square that starts at the coordinate origin (0,0), which is the upper left corner in SVG and Flex. Beware the coordinate origin when translating Inkscape SVG to Flex. The other interesting thing to note is the amazing similarity between Degrafa and FXG. Who knew all my time learning Degrafa will instantly translate to Flex 4 and FXG? Awesome!
SVG Path Shorthand
Here’s a quick overview of shorthand syntax for SVG path data:
Alas, the beta version of FXG does not support the Arc segment type, which I suspect is due to lack of support for arbitrary arcs in the underlying Flash Player rendering engine but I don’t know for sure. Thankfully, Degrafa offers full arc support (thanks Greg!). If you really need to draw arcs in FXG, for stuff like pie wedges, and are unafraid of getting into a cage match with your trigonometry textbook, you can do a good job approximating arcs with cubic Bezier curves. Alternately, you can just use Degrafa once it gets ported to Flex 4. Lastly, using uppercase for the segment type specifies absolute coordinates. This is the format commonly used by Illustrator and Inkscape when exporting drawings to SVG. One can easily switch to relative coordinates by just switching the commands to lowercase, but I would try to avoid it if at all possible as it tends to make one’s head hurt.
The Many Shapes of a Square
All of the squares above, use this shorthand data:
M 0,0 L 100,0 L 100,100 L 0,100 z
First, a Move to set the pen at the origin. Then, a Line right to (100,0), followed by a Line down to (100,100), followed by a Line left to (0,100). Then, a close (z) to return to the origin.
I can drop the commas if I want:
M 0 0 L 100 0 L 100 100 L 0 100 z
Or drop all but the first Line to make a polyline:
M 0,0 L 100,0 100,100 0,100 z
Or use Horizontal Line and Vertical Line:
M 0,0 H 100 V 100 H 0 z
Or even use relative coordinate (which makes my head hurt a little):
m 0,0 l 100,0 l 0,100 l -100,0 z
Curves
Straight lines are cool, but the real fun in life lies in the curves. Cubic Bezier curves should be very familiar to anyone who’s used a vector drawing program. Let’s replace the first segment in our square with a cubic Bezier segment. Now, the SVG shorthand becomes:
M 0,0 C 25,-25 50,25 100,0 L 100,100 L 0,100 z
When rendered, we get this:
The shorthand command says curve to (100,0), but start out heading towards control point #1 at (25,-25) and end up coming in from control point #2 at (50,25).
Arcs
Again, let’s replace the first segment in our square with an arc segment. Now, the SVG shorthand becomes:
M 0,0 A 50,25 0 0,1 100,0 L 100,100 L 0,100 z
When rendered, we get this:
The shorthand command says arc to (100,0), with an x-radius of 50 and a y-radius of 25, with a rotation of 0. The large-arc and sweep flags are a little confusing so you’ll want to review the SVG Spec, § 8.3.8 if you need to get down and dirty with arcs.
Conclusion
I’m a firm believer in “right tool for the job.” So, when in comes to getting SVG path data into Flex, I’m definitely going to use Illustrator or Inkscape as much as possible, and in the future I might just use Catalyst for everything. But there are a few important situations where the Flex developer absolutely must know SVG. First, if you want to do any kind of path morphing (like this), you’ll need precision control over your path segments. And second, if you want to do any dynamic path generation (like building a multi-level radial menu on the fly – which sounds like a good topic for a future post), you’ll need to manually construct your SVG paths.
