android刮刮卡效果

package com.supermap.customview;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

/**
 * Created by Administrator on 2017/5/26 0026.
 */

public class GuaGuaKa extends View {
    private Paint mOutPaint;
    private Path mPath;
    private Canvas mCanvas;
    private Bitmap mBitmap;
    private int mLastY;
    private int mLastX;
    private Bitmap bitmap;

    public GuaGuaKa(Context context) {
        this(context, null);
    }

    public GuaGuaKa(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public GuaGuaKa(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    /**
     * 1——进行一些初始化操作
     */
    private void init() {
        mOutPaint = new Paint();
        mPath = new Path();
        bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.timg);
        /**
         * 设置画笔的属性
         * */
//        ctrl+alt+m抽取方法
        setOutPaint();
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int action = event.getAction();
        int x = (int) event.getX();
        int y = (int) event.getY();
        switch (action) {
            case MotionEvent.ACTION_DOWN:
                mLastX = x;
                mLastY = y;
                mPath.moveTo(mLastX, mLastY);
                break;
            case MotionEvent.ACTION_MOVE:
                int dx = Math.abs(x - mLastX);
                int dy = Math.abs(y - mLastY);
                if (dx > 3 || dy > 3) {
                    mPath.lineTo(x, y);
                }
                mLastX = x;
                mLastY = y;
                break;
            case MotionEvent.ACTION_UP:

                break;
        }
        invalidate();
        return true;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        canvas.drawBitmap(bitmap, 0, 0, null);
        drawPath();
        canvas.drawBitmap(mBitmap, 0, 0, null);
    }

    private void drawPath() {
        mOutPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_OUT));
        mCanvas.drawPath(mPath, mOutPaint);
    }

    /**
     * 2——绘画
     *
     * @param widthMeasureSpec
     * @param heightMeasureSpec
     */
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        int width = getMeasuredWidth();
        int height = getMeasuredHeight();
        /**
         * 初始化bitmap
         */
        mBitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
        /**
         * canvas的操作是在bitmap上
         */
        mCanvas = new Canvas(mBitmap);

        mCanvas.drawColor(Color.GRAY);
        resetBitmapSize(width, height);
    }

    private void resetBitmapSize(int width, int height) {
        int bitmapWidth = bitmap.getWidth();
        int bitmapHeight = bitmap.getHeight();
        float scale = bitmapWidth / bitmapHeight;

        bitmap = scaleBitmap(bitmap, width, (int) scale * width);
    }

    private void setOutPaint() {
        mOutPaint.setColor(Color.RED);
        mOutPaint.setAntiAlias(true);
        mOutPaint.setDither(true);
        mOutPaint.setStrokeJoin(Paint.Join.ROUND);
        mOutPaint.setStrokeCap(Paint.Cap.ROUND);
        mOutPaint.setStyle(Paint.Style.STROKE);
        mOutPaint.setStrokeWidth(10);
    }

    /**
     * 根据给定的宽和高进行拉伸
     *
     * @param origin    原图
     * @param newWidth  新图的宽
     * @param newHeight 新图的高
     * @return new Bitmap
     */
    private Bitmap scaleBitmap(Bitmap origin, int newWidth, int newHeight) {
        if (origin == null) {
            return null;
        }
        int height = origin.getHeight();
        int width = origin.getWidth();
        float scaleWidth = ((float) newWidth) / width;
        float scaleHeight = ((float) newHeight) / height;
        Matrix matrix = new Matrix();
        matrix.postScale(scaleWidth, scaleHeight);// 使用后乘
        /**
         * (Bitmap source, int x, int y, int width, int height,
         Matrix m, boolean filter)
         */
        Bitmap newBM = Bitmap.createBitmap(origin, 0, 0, width, height, matrix, false);
        if (!origin.isRecycled()) {
            origin.recycle();
        }
        return newBM;
    }

}