How to distort an image to any quadrangle?

Question

Do any of you have an idea, how to distort an image in any quadrangle? I want to implement an image, which you can pull any corner in any direction, distorting the image. A

Answer 1

@donmj . I fixed your code.

public class PerspectiveDistortView extends View implements View.OnTouchListener {

private Paint paintRect, paintCircle;
public int LEFT;
public int TOP;
public int RIGHT;
public int BOTTOM;
Point CIRCLE_TOP_LEFT;
Point CIRCLE_TOP_RIGHT;
Point CIRCLE_BOTTOM_LEFT;
Point CIRCLE_BOTTOM_RIGHT;
private int lastX, lastY;
Bitmap image;
Matrix matrix2;
boolean isTouchCirclePoints = true;

public PerspectiveDistortView(Context context) {
    super(context);
    // TODO Auto-generated constructor stub
    init();
}

public PerspectiveDistortView(Context context, AttributeSet attrs) {
    super(context, attrs);
    // TODO Auto-generated constructor stub
    init();
}

public PerspectiveDistortView(Context context, AttributeSet attrs,
                              int defStyle) {
    super(context, attrs, defStyle);
    // TODO Auto-generated constructor stub
    init();
}

private void init() {
    this.setOnTouchListener(this);
    paintRect = new Paint();
    paintRect.setColor(0xffff0000);
    paintRect.setAntiAlias(true);
    paintRect.setDither(true);
    paintRect.setStyle(Paint.Style.STROKE);
    paintRect.setStrokeJoin(Paint.Join.BEVEL);
    paintRect.setStrokeCap(Paint.Cap.BUTT);
    paintRect.setStrokeWidth(3);
    paintCircle = new Paint();
    paintCircle.setColor(0xff000000);
    paintCircle.setAntiAlias(true);
    paintCircle.setDither(true);
    paintCircle.setStyle(Paint.Style.FILL_AND_STROKE);
    paintCircle.setStrokeJoin(Paint.Join.BEVEL);
    paintCircle.setStrokeCap(Paint.Cap.BUTT);

    LEFT = 90;
    TOP = 40;
    RIGHT = 500;
    BOTTOM = 700;
    CIRCLE_TOP_LEFT = new Point(LEFT, TOP);
    CIRCLE_TOP_RIGHT = new Point(RIGHT, TOP);
    CIRCLE_BOTTOM_LEFT = new Point(LEFT, BOTTOM);
    CIRCLE_BOTTOM_RIGHT = new Point(RIGHT, BOTTOM);

    image = BitmapFactory.decodeResource(getResources(), R.drawable.penguins);

    matrix2 = new Matrix();
}

@Override
protected void onDraw(Canvas canvas) {
    // Free Transform bitmap
    int bw = image.getWidth();
    int bh = image.getHeight();

    float[] pts = {
            // source
            0, 0,
            0, bh,
            bw, bh,
            bw, 0,
            // destination
            0, 0,
            0, 0,
            0, 0,
            0, 0};
    pts[8] = CIRCLE_TOP_LEFT.x;
    pts[9] = CIRCLE_TOP_LEFT.y;
    pts[10] = CIRCLE_BOTTOM_LEFT.x;
    pts[11] = CIRCLE_BOTTOM_LEFT.y;
    pts[12] = CIRCLE_BOTTOM_RIGHT.x;
    pts[13] = CIRCLE_BOTTOM_RIGHT.y;
    pts[14] = CIRCLE_TOP_RIGHT.x;
    pts[15] = CIRCLE_TOP_RIGHT.y;

    matrix2.setPolyToPoly(pts, 0, pts, 8, 4);
    canvas.drawBitmap(image, matrix2, null);
    isTouchCirclePoints = false;

    // line left
    canvas.drawLine(CIRCLE_TOP_LEFT.x, CIRCLE_TOP_LEFT.y, CIRCLE_BOTTOM_LEFT.x, CIRCLE_BOTTOM_LEFT.y, paintRect);
    // line top
    canvas.drawLine(CIRCLE_TOP_LEFT.x, CIRCLE_TOP_LEFT.y, CIRCLE_TOP_RIGHT.x, CIRCLE_TOP_RIGHT.y, paintRect);
    // line right
    canvas.drawLine(CIRCLE_TOP_RIGHT.x, CIRCLE_TOP_RIGHT.y, CIRCLE_BOTTOM_RIGHT.x, CIRCLE_BOTTOM_RIGHT.y, paintRect);
    // line bottom
    canvas.drawLine(CIRCLE_BOTTOM_LEFT.x, CIRCLE_BOTTOM_LEFT.y, CIRCLE_BOTTOM_RIGHT.x, CIRCLE_BOTTOM_RIGHT.y, paintRect);
    // circle top left
    canvas.drawCircle(CIRCLE_TOP_LEFT.x, CIRCLE_TOP_LEFT.y, 10, paintCircle);
    // circle top right
    canvas.drawCircle(CIRCLE_TOP_RIGHT.x, CIRCLE_TOP_RIGHT.y, 10, paintCircle);
    // circle bottom left
    canvas.drawCircle(CIRCLE_BOTTOM_LEFT.x, CIRCLE_BOTTOM_LEFT.y, 10, paintCircle);
    // circle bottom right
    canvas.drawCircle(CIRCLE_BOTTOM_RIGHT.x, CIRCLE_BOTTOM_RIGHT.y, 10, paintCircle);
}

@Override
public boolean onTouch(View view, MotionEvent event) {
    lastX = (int) event.getX();
    lastY = (int) event.getY();

    if (inCircle(lastX, lastY, CIRCLE_TOP_LEFT.x, CIRCLE_TOP_LEFT.y, 40)) {
        isTouchCirclePoints = true;
        CIRCLE_TOP_LEFT.set(lastX, lastY);
    } else if (inCircle(lastX, lastY, CIRCLE_TOP_RIGHT.x, CIRCLE_TOP_RIGHT.y, 40)) {
        isTouchCirclePoints = true;
        CIRCLE_TOP_RIGHT.set(lastX, lastY);
    } else if (inCircle(lastX, lastY, CIRCLE_BOTTOM_LEFT.x, CIRCLE_BOTTOM_LEFT.y, 40)) {
        isTouchCirclePoints = true;
        CIRCLE_BOTTOM_LEFT.set(lastX, lastY);
    } else if (inCircle(lastX, lastY, CIRCLE_BOTTOM_RIGHT.x, CIRCLE_BOTTOM_RIGHT.y, 40)) {
        isTouchCirclePoints = true;
        CIRCLE_BOTTOM_RIGHT.set(lastX, lastY);
    }
    invalidate();
    return true;
}

private boolean inCircle(float x, float y, float circleCenterX, float circleCenterY, float circleRadius) {
    double dx = Math.pow(x - circleCenterX, 2);
    double dy = Math.pow(y - circleCenterY, 2);

    if ((dx + dy) < Math.pow(circleRadius, 2)) {
        return true;
    } else {
        return false;
    }
}
}