How to draw an arrowhead in a free handed drawn line in Android?

Question

I need to make a arrow head in a line that is defined by a lot of points, that the user will drawn.

I hope that I could be clear about what is my question.

Thanks.

Note: All the questions/answers that I saw here were to resolve the problem of a line that was defined by two points, taken in the ACTION_DOWN and ACTION_UP. It's different in my case, because I need to take the first point while the line is being drawn.

This is my onTouch() method. It just draw a line defined by where the user touches in the screen.

public boolean onTouch(View v, MotionEvent event) { 
    if(getEditMode()) { 

        float eventX = event.getX();
        float eventY = event.getY();

        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                path.moveTo(eventX, eventY); 

                break;
            case MotionEvent.ACTION_MOVE:
                path.lineTo(eventX, eventY); 

                break;
            case MotionEvent.ACTION_UP:
                             //Here i have to draw an arrow.

                drawCanvas.drawPath(path, paint);
                path.reset();

                invalidate();

                break;

        }

        invalidate();
        return true; 

    } else {
        return false; 

    }
}

Answer 1

So, I found a solution.

I store all the points that construct the line in an arraylist.

After I took a point of the line that would be in the 0.9 * arraylist.size() as reference to draw an arrowhead that follow the line direction.

Here is my onTouch() method and the funciont that I used to draw the arrow.

public boolean onTouch(View v, MotionEvent event) {
    if(getEditMode()) {
        float eventX = event.getX();
        float eventY = event.getY();

        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN: {
                path.moveTo(eventX, eventY);

                pList.clear(); // When I start a line need to clear the previous coorfinates.

                break;

            }

            case MotionEvent.ACTION_MOVE: {
                int hSize = event.getHistorySize();

                path.lineTo(eventX, eventY);

                PointF aux, auxH;

                if(darrow) {
                    if(hSize > 0) { // If movement is too fast.
                        for(int i = 0; i < hSize; i++) {
                            auxH = new PointF(event.getHistoricalX(i), event.getHistoricalY(i));

                            pList.add(auxH);

                        }

                    }

                    aux = new PointF(eventX, eventY);

                    pList.add(aux);

                }

                break;

            }   

            case MotionEvent.ACTION_UP: {
                pend.x = eventX;
                pend.y = eventY;

                if(darrow) { // If need to draw an arrow head to the end of the line;
                    arrowPath = drawArrow(pend); // Store the right arrowhead to a path.

                }

                drawCanvas.drawPath(path, paint);
                drawCanvas.drawPath(arrowPath, paint);

                path.reset();
                arrowPath.reset();

                invalidate();

                break;

            }

        }

        invalidate();

        return true;

    } else {
        return false;

    }

}

And the drawArrow(PointF) function:

private Path drawArrow(PointF pfinal) {
    float dx, dy;
    PointF p1, p2;
    PointF pstart;
    Path auxPath = new Path();

    if(pList.size() > 0) {
        PointF[] auxArray = pList.toArray(new PointF[pList.size()]);

        int index = (int)(auxArray.length * 0.9);

        Log.d(msg, "Size: " + auxArray.length + " | index: " + index);

        pstart = auxArray[index];

        dx = pfinal.x - pstart.x;
        dy = pfinal.y - pstart.y;

        float length = (float)Math.sqrt(dx * dx + dy * dy);

        float unitDx = dx / length;
        float unitDy = dy / length;

        final int arrowSize = 10;

        p1 = new PointF(
                (float)(pfinal.x - unitDx * arrowSize - unitDy * arrowSize),
                (float)(pfinal.y - unitDy * arrowSize + unitDx * arrowSize));

        p2 = new PointF(
                (float)(pfinal.x - unitDx * arrowSize + unitDy * arrowSize),
                (float)(pfinal.y - unitDy * arrowSize - unitDx * arrowSize));

        auxPath.moveTo(pfinal.x, pfinal.y);
        auxPath.lineTo(p1.x, p1.y);
        auxPath.moveTo(pfinal.x, pfinal.y);
        auxPath.lineTo(p2.x, p2.y);

        auxPath.close();

    }

    return auxPath;

}