svg animation path direction - svg

Question

I'm using svg animation tags to animate a group tag along the coordinates of a path tag. Unfortunately, the animation is running in the opposite direction to what I require (I.E going from b to a instead of a to b). Does there exist any attribute which would amend this, something like:
<animateMotion
xlink:href="#group1"
dur="6s"
fill="freeze"
rotate="auto-reverse"
direction="reverse"
>
<mpath xlink:href="#path1" />
</animateMotion>
I know this could be achieved with snap or raphael but as far as I know it's not possible to use anything to the effect of 'rotate="auto-reverse"' in those libraries.
Alternatively, is there a way to reverse the way my path is calculated; can this be achieved with any software?

Answer 1

You could use the keyPoints attribute, along with keyTimes.
<?xml version="1.0"?>
<svg width="120" height="120" viewBox="0 0 120 120"
xmlns="http://www.w3.org/2000/svg" version="1.1"
xmlns:xlink="http://www.w3.org/1999/xlink" >
<path d="M10,110 A120,120 -45 0,1 110 10 A120,120 -45 0,1 10,110"
stroke="lightgrey" stroke-width="2"
fill="none" id="theMotionPath"/>
<!-- Here is a green circle which will be moved along the motion path. -->
<circle cx="" cy="" r="5" fill="green">
<!-- Define the motion path animation -->
<animateMotion dur="6s" repeatCount="indefinite" keyPoints="0;1" calcMode="linear"
keyTimes="0;1">
<mpath xlink:href="#theMotionPath"/>
</animateMotion>
</circle>
<!-- Here is a red one, using the same motionPath but reversed thanks to keyPoints -->
<circle cx="" cy="" r="5" fill="red">
<animateMotion dur="6s" repeatCount="indefinite" keyPoints="1;0" calcMode="linear"
keyTimes="0;1">
<mpath xlink:href="#theMotionPath"/>
</animateMotion>
</circle>
</svg>