How to animate a filled triangle (drawn by a path) in Android Studio - android-studio

Question

I'm trying to build a jigsaw-like app for Android that involves the user moving polygonal pieces around the screen by touch event.
I can draw - for example - a triangle, and fill it. I can also move it smoothly round the screen but it leaves a trace - so that the screen rapidly fills up :-(
So I am wondering how to adjust the onDraw method so that the previous positions of the triangle are not included. Or is there some other technique? The question has been asked once before but did not get a satisfactory answer. I am quite new to Android work so I am sure a kind expert will be able to point me in the right direction!
The view:
public class GameView extends View {
public Triangle T1;
Paint paint = new Paint();
private Path path;
public GameView(Context context) {
super(context);
paint.setStyle(Paint.Style.FILL);
paint.setColor(Color.GREEN);
initTriangle();
}
public void initTriangle() {
int T1Points[][] = new int[3][2];
T1Points[0][0] = -200;
T1Points[0][1] = -100;
T1Points[1][0] = 200;
T1Points[1][1] = -100;
T1Points[2][0] = 0;
T1Points[2][1] = 100;
float[] position = new float[2];
position[0] = (float) 200.0;
position[1] = (float) 100.0;
T1 = new Triangle("T1", T1Points, position);
path = T1.getPath();
}
#Override
public boolean onTouchEvent(MotionEvent event) {
float[] pos = new float[2];
pos[0] = event.getX(); //nextx;
pos[1] = event.getY(); //nexty;
T1.setPosition(pos );
Path path = new Path();
path = T1.getPath();
postInvalidate();
return true;
}
protected void onDraw(Canvas canvas) {
canvas.drawPath(path, paint);
}
}
Triangle class:
public class Triangle {
public int[][] myPoints;
public Path path;
public String myname;
public float[] position;
public Triangle (String name, int[][] newpoints, float[] posn) {
myPoints = new int[4][2];
int i;
for (i = 0; i < 3; i++) {
myPoints[i][0] = newpoints[i][0];
myPoints[i][1] = newpoints[i][1];
}
myPoints[3][0] = newpoints[0][0]; // closed circuit for future needs
myPoints[3][1] = newpoints[0][1];
path = new Path();
position = new float[2];
position[0] = posn[0];
position[1] = posn[1];
myname = name;
updatePath();
}
public void setPosition(float[] newPosition){
position[0] = newPosition[0];
position[1] = newPosition[1];
updatePath();
}
public void updatePath(){
int startx = myPoints[0][0] + Math.round(position[0]);
int starty = myPoints[0][1] + Math.round(position[1]);
path.moveTo(startx,starty);
for (int i = 1; i < myPoints.length; i++)
{
int newx = myPoints[i][0] + Math.round(position[0]);
int newy = myPoints[i][1] + Math.round(position[1]);
path.lineTo(newx,newy);
}
path.close();
}
public Path getPath() {
return path;
}
}
Main Activity:
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
uk.mydomain.animatedtriangle.GameView gameView = new uk.mydomain.animatedtriangle.GameView(this);
RelativeLayout relativeLayout = new RelativeLayout(this);
RelativeLayout.LayoutParams relativeParams = new RelativeLayout.LayoutParams(
RelativeLayout.LayoutParams.MATCH_PARENT,
RelativeLayout.LayoutParams.MATCH_PARENT);
relativeLayout.setLayoutParams(relativeParams);
setContentView(relativeLayout);
relativeLayout.addView(gameView);
}

Answer 1

Sorted! Just needed to add a path.reset() at the end of onDraw.