Efficient Rendering of Duplicates with Blend Mode "Add"

What I want to do is move an object and have it leave a color trail behind it. After several evenings of mucking about, I’ve succeeded in getting what I want. The problem is that rendering it is glacially slow – my 2.5 second sequence takes nearly five minutes to render on my 4.0 GHz machine, leading me to believe that my approach is woefully inefficient.

I’ve attached a simplified example of what I’m trying to do which, when rendered at the 2.0 second mark, looks like this:

What I’m not really understanding is the interaction between the Duplicate layer, group layers, and Blend Modes. I want each piece of the trail to be "Add"ed to the canvas. However, near as I’ve been able to work out, group layers create their own sort of virtual canvas, which gets combined with the other layers later on. Thus, if the layers inside a group have a two-operand Blend Mode such as “Add” or “Subtract,” the operation will have nothing as its second argument, causing nothing to be rendered.

Eventually, through trial and error, I discovered I could get what I wanted by doing the following:

  • Place a Solid Color layer at the bottom of the group.
  • Change the Blend Mode of all polygon/primitive layers inside the group to Composite.
  • Change the Blend Mode of the Duplicate layer (outside the group) to Add.

While this works and achieves the visual effect I wanted, it’s damned slow to render. My guess is that the Duplicate layer is rendering the Solid Color and polygon layers n times, then Add-ing the intermediate results together (in fact, it should only need to render the Solid Color once). So I was wondering if there was something especially inefficient about my setup, or if there was a trick I could use to speed things up. I’m using Synfig v1.0.2.
trailtest.sif (18.1 KB)

Hello and welcome here …

I did’nt take a look “inside” your project, but i did render it, threw synfig 1.0.2 / mp4 / ffmpeg - h264 loosless / quality 3 / antialias 1 … and was not so extremely long…

Did you take a look to the rendering walk through page … about quality and antialias …

By the way … nice effect !

The example I posted was simplified. The actual figure is about ten region layers imported from Inkscape. And the final render looks a little bit like this :slight_smile: . But like I said, it took ten minutes to render the spinny bit at the beginning.

Not yet; I’ll have a look.

Thank you kindly!