Android drawBitmapMesh 扭曲图像

本文内容摘自《疯狂Android讲义 第3版》李刚 著

package shortcut.song.com.myapplication;import android.content.Context;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.graphics.Canvas;import android.graphics.Color;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.util.AttributeSet;import android.view.MotionEvent;import android.view.View;public class BitmapMeshActivity extends AppCompatActivity {    private Bitmap bitmap;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(new MeshView(this, R.drawable.qiao));    }    class MeshView extends View{        //定义两个常量，指定该图片横向、纵向被划分为20格        private final int WIDTH = 20;        private final int HEIGHT = 20;        //计录图片上包含441个顶点        private final int COUNT = (WIDTH + 1) * (HEIGHT + 1);        //定义一个数组，保存Bitmap上21 * 21个点坐标        private final float[] verts = new float[COUNT * 2];        //定义一个数组，记录Bitmap上的20 * 20个点经过扭曲后的坐标        private final float[] orig = new float[COUNT * 2];        public MeshView(Context context, int drawableId)        {            super(context);            setFocusable(true);            //根据指定资源加载图片            bitmap = BitmapFactory.decodeResource(context.getResources(), drawableId);            //获取图片宽度，高宽度            float bitmapWidth = bitmap.getWidth();            float bitmapHeight = bitmap.getHeight();            int index = 0;            for (int y = 0; y <= HEIGHT; y++){                float fy  = bitmapHeight * y / HEIGHT;                for (int x = 0; x <= WIDTH; x++) {                    float fx = bitmapWidth * x /WIDTH;                    //初始化orig, verts两个数组。初始化后orig, verts 两个数组均匀地保存了20 * 21个点的x,y坐标                    orig[index * 2 + 0] = verts[index * 2 + 0] = fx;                    orig[index * 2 + 1] = verts[index * 2 + 1] = fy;                    index += 1;                }            }            //设置背景色            setBackgroundColor(Color.WHITE);       }        @Override        protected void onDraw(Canvas canvas) {            //super.onDraw(canvas);            //对Bitmap按verts数组进行扭曲            //从从第一个点（由第5个参数0控制）开始扭曲            canvas.drawBitmapMesh(bitmap, WIDTH, HEIGHT, verts, 0, null, 0, null);        }        //根据触摸事件的位置计算verts数组里的各元素值        private void warp(float cx, float cy)        {            for (int i=0; i < COUNT * 2; i += 2)            {                float dx = cx - orig[i + 0];                float dy = cy - orig[i + 1];                float dd = dx * dx + dy * dy;                //计算每个坐标点与当前点（cx, cy）之间的距离                float d = (float)Math.sqrt(dd);                //计算扭曲度，距离当前点(cx, cy)越远，越扭曲                float pull = 80000 / (float)(dd * d);                //对verts 数组，保存bitmap上21 *21 个点经过扭曲后的坐标，重新赋值                if(pull >= 1)                {                    verts[i + 0] = cx;                    verts[i + 1] = cy;                }else                {                    verts[i + 0] = orig[i + 0] + dx * pull;                    verts[i + 1] = orig[i + 1] + dy * pull;                }            }            //通知组件重绘            invalidate();        }        @Override        public boolean onTouchEvent(MotionEvent event) {            warp(event.getX(), event.getY());            return true;        }    }}