import processing.awt.PGraphicsJava2D;

// Create 3 x 3 matrix to store camera info.
PMatrix2D camMat = new PMatrix2D();

/* ... */

void draw() {
  camera(camMat, hero.x, hero.y, 0.0, 1.0, 1.0);
  /* ... */
}

PMatrix2D camera(PMatrix2D cameraMatrix,
  float tx, float ty, float angle,
  float zoomW, float zoomH) {

  // The default matrix is
  //  1, 0, 0,
  //  0, 1, 0,
  //  0, 0, 1
  // with the bottom row omitted because
  // it doesn't change in 2D transformations.

  // This shifts the camera to look at the
  // screen's center.
  cameraMatrix.set(
    1.0, 0.0, width * 0.5,
    0.0, 1.0, height * 0.5);
  cameraMatrix.rotate(angle);
  cameraMatrix.scale(zoomW, zoomH);
  cameraMatrix.translate(-tx, -ty);

  // Set this PApplet renderer's matrix.
  setMatrix(cameraMatrix);
  return cameraMatrix;
}

// Static variant of the above.
// Supply the 2D renderer from the outside.
static PMatrix2D camera(PGraphicsJava2D rndr,
  PMatrix2D cameraMatrix,
  float tx, float ty, float angle,
  float zoomW, float zoomH) {
  /* ... */
  rndr.setMatrix(cameraMatrix);
  return cameraMatrix;
}