How should I go about rendering to an offscreen image in P5 alpha?

this works nicely in p68...

Code:

BGraphics buffer;

void setup() {
  size(200, 200);
  buffer=new BGraphics(180,180);
  buffer.defaults();
  buffer.background(255);
  buffer.stroke(0);
}

void loop() {
  buffer.line(mouseX-10, mouseY-10, pmouseX-10, pmouseY-10);
  image(buffer,10,10,180,180);
} 

...but I get no sign of life from this in p90...

Code:

PGraphics buffer;

void setup() {
  size(200, 200);
  buffer=new PGraphics(180,180,this);
  buffer.defaults();
  buffer.background(255);
  buffer.stroke(0);
}

void draw() {
  buffer.line(mouseX-10, mouseY-10, pmouseX-10, pmouseY-10);
  image(buffer,10,10,180,180);
} 

p.s. I've tried sandwiching the buffer drawing operations with buffer.beginFrame() and buffer.endFrame()

p.p.s. Alternatively, is there a p5 friendly way of temporarily setting a clipping rectangle?

p.p.p.s. I feel like a newb all over again and I love it.