Lyraspace » Blog Archive » Spark ScrubBar bufferedArea bug

Sep 17

Spark ScrubBar bufferedArea bug

I discovered a bug in the Spark ScrubBar class that I thought I’d better document. It’s a real git!

Firstly I noticed that despite setting the bufferEnd property of the class I wasn’t seeing any results. So I watched the numbers and sure enough the bufferEnd property was being set as my media loaded and was significantly larger than the playhead value which made sense.

So then I figured the skin part wasn’t being rendered so I forced a width on it in the skin class and sure enough it was rendered. I soon realised that the bufferedArea was being drawn and was being adjusted over time. Unfortunately its width was being set to exactly the same size as the playedArea element so it was hidden underneath.

So then I did some digging and I traced the calculation of the size of the skin part down to a private method in the ScrubBar class called ‘calculateAreaSize’. Both the playedArea and the bufferedArea get their sizes from this method as the ‘value’ and ‘bufferEnd’ properties change.

The problem is that the argument passed into this method is called ‘value’ which is the same name as the class property ‘value’ that is used to determine the width of playedArea. So when this method was being used to also calculate the width of bufferedArea it was yielding the same results.

The solution is to sub-class ScrubBar and then add the following methods …

override protected function updateSkinDisplayList():void
{
super.updateSkinDisplayList();
sizeBufferedArea(newCalculateAreaSize(bufferedEnd));
sizePlayedArea(newCalculateAreaSize(value));
}
protected function newCalculateAreaSize(v:Number):Number
{
var trackPos:Number = track.getLayoutBoundsX();
var trackSize:Number = track.getLayoutBoundsWidth();
var thumbSize:Number = thumb.getLayoutBoundsWidth();
var range:Number = maximum – minimum;
var thumbPos:Number = (range > 0) ? (v – minimum) * ((trackSize – thumbSize) / range) : 0;
return thumbSize + thumbPos;
}