Question: What value fed to strokeWidth() will give a stroke width of one pixel regardless of the current scale() setting?

Answer: 
I think `strokeWeight(0)` should work. Here is an example:

```
void setup() {
   size(100,100);
   noFill();
   scale(10);
   // 1st square, stroke will be 10 pixels
   translate(3,3);
   strokeWeight(1);
   beginShape();
   vertex(-1.0, -1.0);
   vertex(-1.0,  1.0);
   vertex( 1.0,  1.0);
   vertex( 1.0, -1.0);
   endShape(CLOSE);
   // 2nd square, stroke will be 1 pixel
   translate(3,3);
   strokeWeight(0);
   beginShape();
   vertex(-1.0, -1.0);
   vertex(-1.0,  1.0);
   vertex( 1.0,  1.0);
   vertex( 1.0, -1.0);
   endShape(CLOSE);
}

```
None.

The whole point of `scale()` is that it, well, scales everything.

You might want to draw things in layers: draw one scaled layer, and one unscaled layer that contains the single-pixel-width lines. Then combine those layers.

That won't work if you need your layers to be mixed, such as an unscaled line on top of a scaled shape, on top of another scaled line. In that case you'll just have to unscale before drawing your lines, then scale again to draw your shapes.