var canvas;

        function setup() {
          // put drawing code here
          canvas = createCanvas(windowWidth, windowHeight);
          background(255);

          button = createButton("Image Speichern");
          button.mousePressed(saveImage)
          button.position(windowWidth - 180, windowHeight - 50)
        }

        function draw() {
          // put drawing code here
          stroke(255);
          strokeWeight(1);
          fill(0);
          if (mouseIsPressed === true) {
            stroke(0);
            line(mouseX, mouseY, pmouseX, pmouseY);
          } else {
            stroke(255);
          }
        }

        function saveImage() {
         saveCanvas('Sketch', 'jpg');
        }