Smil animations on svg - svg

Question

Greeting to all,
I recently found myself reading the following article (http://apike.ca/prog_svg_smil.html) and more specifically the "Animation Element - animateMotion".
Is there a way of "telling" the moving "marker" to accelerate or decelerate on specific portions (segments) of the path, or is its speed always defined by the "dur" attribute (in seconds)?
Thanks in advance.

Answer 1

Controlling the animation timing is provided by the calcMode, keyTimes, keySplines and keyPoints attributes of svg animation elements such as animateMotion. Basically you specify points on a normalized timeline and tell svg how to map them onto the progress measured on a normalized timeline as well. you also specify how to interpolate between the support points given. for smooth animations you would chose calcMode="spline".
the relevant references are:
svg(animateMotion)
svg(keyPoints)
smil(CalcModes)
smil(keyTimes)
for demo purposes, have a look at an animated line tracking demo (online here, click on the dark bar; example taken from here, timing control added):
<?xml version="1.0" encoding="ISO-8859-1" 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"
xmlns:xlink="http://www.w3.org/1999/xlink" xml:space="preserve"
width="200" height="200"
viewBox="0 0 200 200" >
<!-- Matthew Bystedt http://apike.ca 2012 -->
<!-- Pattern Definition -->
<defs>
<pattern id="rulerPattern" patternUnits="userSpaceOnUse"
x="0" y="0" width="10" height="10"
viewBox="0 0 10 10" >
<line x1="0" y1="0" x2="10" y2="0" stroke="lightblue" fill="none" stroke-dasharray="2,2" />
<line x1="0" y1="0" x2="0" y2="10" stroke="lightblue" fill="none" stroke-dasharray="2,2" />
</pattern>
<marker id="marker2" viewBox="0 0 10 10" refX="1" refY="5"
markerUnits="strokeWidth" orient="auto"
markerWidth="4" markerHeight="3">
<polyline points="0,0 10,5 0,10 1,5" fill="darkgreen" />
</marker>
</defs>
<!-- Background -->
<rect x="0" y="0" width="100%" height="100%" fill="url(#rulerPattern)" stroke="black" />
<!-- Path Line Example -->
<path id="myAniPath" d="M10,150 A15 15 180 0 1 70 140 A15 25 180 0 0 130 130 A15 55 180 0 1 190 120 A15 10 170 0 1 10 150" stroke="lightgreen" stroke-width="2" fill="none" marker-mid="url(#marker2)" />
<rect x="-10" y="-5" width="20" height="10" fill="none" stroke="black" >
<animateMotion begin="startButton.click" dur="10s" calcMode="spline" keyTimes="0; 1" keySplines=".75 0 .25 1" repeatCount="1" rotate="auto" fill="freeze">
<mpath xlink:href="#myAniPath" />
</animateMotion>
</rect>
<rect id="startButton" x="20" y="20" width="60" height="20" fill="green" />
<line stroke="black" stroke-width="2" x1="20" y1="20" x2="20" y2="40" >
<animate begin="startButton.click" attributeName="x1" from="20" to="80" dur="10s" repeatCount="1" fill="freeze" />
<animate begin="startButton.click" attributeName="x2" from="20" to="80" dur="10s" repeatCount="1" fill="freeze" />
</line>
</svg>