以下是一个使用setPolyToPoly()方法来裁剪图像的示例代码：

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.PointF;
import android.graphics.drawable.BitmapDrawable;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

public class CropImageView extends View {
    private Bitmap mBitmap;
    private Matrix mMatrix;
    private int mImageWidth, mImageHeight;
    private PointF[] mPolyPoints;
    private int mPolyPointCount;

    public CropImageView(Context context) {
        super(context);
        init();
    }

    public CropImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    private void init() {
        // 加载图像
        mBitmap = ((BitmapDrawable) getResources().getDrawable(R.drawable.your_image)).getBitmap();
        mImageWidth = mBitmap.getWidth();
        mImageHeight = mBitmap.getHeight();

        // 设置初始变换矩阵
        mMatrix = new Matrix();
        mMatrix.setTranslate(0, 0);

        // 设置多边形顶点
        mPolyPoints = new PointF[4];
        mPolyPointCount = 0;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        // 绘制图像
        canvas.drawBitmap(mBitmap, mMatrix, null);

        // 绘制多边形边界线
        if (mPolyPointCount > 0) {
            for (int i = 0; i < mPolyPointCount - 1; i++) {
                canvas.drawLine(mPolyPoints[i].x, mPolyPoints[i].y, 
                        mPolyPoints[i + 1].x, mPolyPoints[i + 1].y, null);
            }
            // 绘制多边形最后一条边
            canvas.drawLine(mPolyPoints[mPolyPointCount - 1].x, mPolyPoints[mPolyPointCount - 1].y,
                    mPolyPoints[0].x, mPolyPoints[0].y, null);
        }
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                // 添加顶点
                if (mPolyPointCount < 4) {
                    mPolyPoints[mPolyPointCount] = new PointF(event.getX(), event.getY());
                    mPolyPointCount++;
                }
                break;
            case MotionEvent.ACTION_MOVE:
                // 移动顶点
                if (mPolyPointCount > 0) {
                    mPolyPoints[mPolyPointCount - 1].set(event.getX(), event.getY());
                }
                break;
            case MotionEvent.ACTION_UP:
                // 完成多边形裁剪
                if (mPolyPointCount == 4) {
                    cropImage();
                }
                break;
        }

        invalidate();
        return true;
    }

    private void cropImage() {
        // 创建裁剪后的图像
        Bitmap croppedBitmap = Bitmap.createBitmap(mImageWidth, mImageHeight, Bitmap.Config.ARGB_8888);
        Canvas croppedCanvas = new Canvas(croppedBitmap);

        // 设置裁剪区域
        float[] src = new float[mPolyPointCount * 2];
        float[] dst = new float[mPolyPointCount * 2];
        for (int i = 0; i < mPolyPointCount; i++) {
            src[i * 2] = mPolyPoints[i].x;
            src[i * 2 + 1] = mPolyPoints[i].y;
            dst[i * 2] = i * 100;  // 设置裁剪后的图像顶点x坐标
            dst[i * 2 + 1] = i * 100;  // 设置裁剪后的图像顶点y坐标
        }

        Matrix polyMatrix = new Matrix();
        polyMatrix.setPolyToPoly(src, 0, dst, 0, mPolyPointCount);
        croppedCanvas.drawBitmap(mBitmap, polyMatrix, null);

        // 使用裁剪后的图像
        mBitmap = croppedBitmap;
        mImageWidth = mBitmap.getWidth();
        mImageHeight = mBitmap.getHeight();

        // 重置多边形顶点
        mPolyPointCount = 0;
    }
}

请注意，此示例中的R.drawable.your_image应替换为您自己的图像资源