metaball part 3

gistfile1.js

function metabalize(){
    var imageData = tempCtx.getImageData(0,0,width,height),
        pix = imageData.data;
    
    for (var i = 0, n = pix.length; i <n; i += 4) {
        // Checks threshold
        if(pix[i+3]<threshold){
            pix[i+3]=0;
        }
    }
    ctx.putImageData(imageData, 0, 0);    
}