HTML and CSS Reference
In-Depth Information
onclick="alert('Penguin Click');"Click
ontouchstart="alert('Penguin Touch');" />
<text x="75" y="125" text-anchor="middle"
font-family="Verdana" font-size="10" fill="black" >
A tilted birdhouse
As mentioned, SVG provides a number of different primitives for drawing. Unlike Canvas, after you create
an element, it sticks around in the scene graph the same way that DOM elements do. You can move the element
around by modifying its x and y properties or by adding a transform property. SVG elements can also have
event handlers attached. If you click the image of the penguin on the desktop, you can trigger the onclick
handler. If you touch it on a WebKit device, you'll trigger a “Penguin Touch” alert.
Each primitive element also has a set of properties specific to the element in question. Although a full over-
view of all the details of the SVG spec is out of scope for a single chapter, the following sections discuss some
of the details of a few of the primitive elements used previously. If you want to learn more about SVG, check
out the specification at .
NOTE Android devices, as of this writing, don't support the ontouchstart event handler being added as
an attribute, but they do work when added manually via addEventListener .
The base <svg> container element has already been briefly described, but a couple of additional attributes will
be important later in the chapter. (Attributes in SVG are case-sensitive, so make sure you match the case shown
in the text.) The width and height attributes are self-explanatory because they define the width and height
of the element inside of the HTML document. The viewBox attribute (the “B” in box is capitalized) is inter-
esting. It defines the portion of the SVG document that is visible inside of the SVG container. viewBox takes
four integer parameters (separated by spaces, not commas):
<svg width='WIDTH' height='HEIGHT' viewBox="X Y WIDTH HEIGHT"> ...
As you may have figured out, from a game perspective you can use the viewBox as a camera into your
game. If you set a WIDTH and HEIGHT in the viewBox that is smaller than the WIDTH and HEIGHT on the
<svg> element, objects in the SVG container appear zoomed in. If you set the WIDTH and HEIGHT to be lar-
ger than the container, elements zoom out. Setting the X and Y parameters essentially pans the camera around
the page.
If the aspect ratio of the <svg> element and the viewBox don't line up, how the content displays inside of
the container depends on the value of the preserveAspectRatio attribute. The default options ensure that
the content is scaled down, so the entire viewBox is visible inside of the container, with content centered in the
x and y direction. preserveAspectRatio has a lot of configurable values, so if you need control over how
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