Faulty diff calculation for transparency

[cburgmer]

Hey, while looking for something unrelated I stumbled upon this line of code:

cData[i+3] = Math.abs(255 - aData[i+3] - bData[i+3]);

I think what we want is this:

cData[i+3] = Math.abs(255 - Math.abs(aData[i+3] - bData[i+3]));

[hardchor]

Agreed, I observed that comparison of transparent fields doesn't seem to work as expected.

[cburgmer]

See pull request #19

[cburgmer]

PR is merged.