warp_perspective.pde

import gab.opencv.*;
import org.opencv.imgproc.Imgproc;
import org.opencv.core.MatOfPoint2f;
import org.opencv.core.Point;
import org.opencv.core.Size;

import org.opencv.core.Mat;
import org.opencv.core.CvType;

OpenCV opencv;
ArrayList<PVector> inputPoints;

boolean perspectiveWarped = false;

void setup() {
  opencv = new OpenCV(this, "test.png");
  inputPoints = new ArrayList<PVector>();
  size(opencv.width, opencv.height);
}

void draw() {

  if (inputPoints.size() >= 4) {
    if (!perspectiveWarped) {
      opencv.setGray(warpPerspective(opencv.getGray(), inputPoints, width, height));  
      perspectiveWarped = true;
    }
  }

  image(opencv.getOutput(), 0, 0);

  noFill();
  stroke(255);

  beginShape();
  for (PVector p : inputPoints) {
    vertex(p.x, p.y);
    ellipse(p.x, p.y, 3, 3);
  }
  endShape();
}

void mousePressed() {
  inputPoints.add(new PVector(mouseX, mouseY));
}

Mat warpPerspective(Mat warped, ArrayList<PVector> points, int w, int h) {
  Mat transform = getPerspectiveTransformation(points, w, h);
  Mat unwarped = new Mat(w, h, CvType.CV_8UC1);    
  Imgproc.warpPerspective(warped, unwarped, transform, new Size(w, h));
  return unwarped;
}

Mat getPerspectiveTransformation(ArrayList<PVector> points, int w, int h) {
  Point[] canonicalPoints = new Point[4];
  canonicalPoints[0] = new Point(w, 0);
  canonicalPoints[1] = new Point(0, 0);
  canonicalPoints[2] = new Point(0, h);
  canonicalPoints[3] = new Point(w, h);

  MatOfPoint2f canonicalMarker = new MatOfPoint2f();
  canonicalMarker.fromArray(canonicalPoints);

  Point[] p = new Point[4];
  for (int i = 0; i < 4; i++) {
    p[i] = new Point(points.get(i).x, points.get(i).y);
  }
  MatOfPoint2f marker = new MatOfPoint2f(p);
  return Imgproc.getPerspectiveTransform(marker, canonicalMarker);
}