Delay before starting to draw

Ok, I have made a rather lovely filter that does stitching on a bit of fabric, however there's something that annoying me about it.

It only takes about 1 minute to render a 512x512 on my laptop with no AA, however, 30 seconds of that is it doing nothing at all before the first little square in rendered. Which is really annoying, if I tweak the colour I have to wait 30s before I can see a single square of the new colour. Once it starts going, the rest of the squares render pretty fast.

I've never seen a filter have such a long delay before the first square is drawn on an otherwise quick filter, can anyone help me figure out the reason for this big delay?

Stitched Canvas4.ffxml

Thanks, that's really great, it's much faster, and the new position for the noise distort is far more sensible, it makes the threads way more unique than how it was before. It only takes 55 seconds for me, with AA on, which I think is about right for a filter of this kind of detail.

Yea, the fade fabric option was an afterthought I added after playing about with some denim fabrics, I didn't like having those blurs there, I've mostly kept it switched off, I can't get it to give the kind of jeans pocket type fade I want anyway.

With my own playing, I found that taking off the blur for the height map took about 10 seconds off (about 5 when I did it on your version), however the surface was intolerably rough after that, I may replace the whole of the fabric part if I can think of a way to make a smooth enough pattern without blur. The other blur that makes a shadow around the thread, I tried thking that out too, also a bit faster, but again, I just don't like it without.

I also realised I've made something of boo-boo, I added the colour right at the start for the stitching, then took the bump from that, so, if you use dark thread, it goes wrong.. I'll have to make it white then use a threshold or something to add the colour at the end.

Thanks for the help. I've not really considered the order of components that much, I've only been thinking about which ones the wiki says are fast or slow.

I decided to redo the whole thing from the start and do the canvas and the string in a different way, so I had it starting off making the bits for the height map in the smoothest way possible so that I could eliminate the blur, so now it only takes 5 seconds to get the the first square. Hooray!