Android手绘效果实现

效果图

原理

大概介绍一下实现原理。首先你得有一张图（废话~）,接下来就是把这张图的轮廓提取出来，轮廓提取算法有很多，本人不是搞图像处理的，对图像处理感兴趣的童鞋可以查看相关资料。如果你有好的轮廓提取算法，也可以把源码中的算法替换掉，我们采用的轮廓提取算法是Sobel边缘检测。网上的实现有很多，我懒得去实现一遍，github有开源的实现，直接下载了:GraphicLib.本文不具体介绍轮廓提取算法。得到轮廓图以后，接下来要做的是，按照线条的走势，一个一个像素点绘制出来。注意，一定要按照线条的走势显示对应的像素点，如果用两个嵌套的for循环，动画会像网速不好时浏览器显示图片一样。难点就在于此，如何把像素点按照线条方向绘制。接下来我们一起研究。

代码实现

如何让绘制的点不会跳远太远，使之连贯起来？首先，对于一个刚绘制完成的点，接下来要绘制的点肯定要选择离它最近的点，这样肯定是最佳的下一个绘制点。因此，只要我们找到最近的点就可以，寻找最近的点，可以通过以圆的方式不断改变半径的大小进行探测。但是用圆的话需要各种三角函数运算，影响效率。我们可以换一种方法：根据当前的点可以轻松得到每一层以该点为中心的正方形，一层层遍历，直到找到需要的点就是我们要的点。遍历的方法很简单，就是比较对应的正方形的上下左右四条边上面的像素点。如下图所示：

接下来看看如何用代码去实现寻找最近的点：

//获取离指定点最近的一个未绘制过的点private Point getNearestPoint(Point p) {if (p == null) return null;//以点p为中心，向外扩大搜索范围，每次搜索的是与p点相距add的正方形for (int add = 1; add < mSrcBmWidth && add < mSrcBmHeight; add++) {//int beginX = (p.x - add) >= 0 ? (p.x - add) : 0;int endX = (p.x + add) < mSrcBmWidth ? (p.x + add) : mSrcBmWidth - 1;int beginY = (p.y - add) >= 0 ? (p.y - add) : 0;int endY = (p.y + add) < mSrcBmHeight ? (p.y + add) : mSrcBmHeight - 1;//搜索正方形的上下边for (int x = beginX; x <= endX; x++) {if (mArray[x][beginY]) {//标记当前点已经访问过mArray[x][beginY] = false;return new Point(x, beginY);}if (mArray[x][endY]) {//标记当前点已经访问过mArray[x][endY] = false;return new Point(x, endY);}}//搜索正方形的左右边for (int y = beginY + 1; y <= endY - 1; y++) {if (mArray[beginX][y]) {//标记当前点已经访问过mArray[beginX][beginY] = false;return new Point(beginX, beginY);}if (mArray[endX][y]) {//标记当前点已经访问过mArray[endX][y] = false;return new Point(endX, y);}}}return null;}

任何一个点，只要还存在没有绘制过的点，就一定能找得到与它最近的点，如果找不到，说明所有的点已经绘制完毕。为了防止查找到重复的点，需要把访问过的点做上记号（即设为false）。我们需要把整张图中每一个像素点位置作好记号，标记哪些点是需要绘制，哪些点是不需要绘制或者是已经绘制过。用一个boolean[][]型数组保存。还需要记录最后一次访问的点，以便继续下一次的绘制。根据最后一次访问的点继续寻找最近点，反复迭代，把所有的点绘制完成后，整张图就出来了。程序开始时，将最后一次访问的点初始化为左上角的点。

   private Point mLastPoint = new Point(0, 0);
//获取下一个需要绘制的点private Point getNextPoint() {mLastPoint = getNearestPoint(mLastPoint);return mLastPoint;}

接下来是将点绘制到Bitmap上，在将Bitmap绘制到SurfaceView的Canvas上。这里这么做的目的是，SurfaceView内部使用了双缓存，直接绘制到SurfaceView的Canvas可能会闪屏。

/*** //绘制* return :false 表示绘制完成，true表示还需要继续绘制*/private boolean draw() {mPaint.setStyle(Paint.Style.STROKE);mPaint.setColor(Color.BLACK);//获取count个点后，一次性绘制到bitmap在把bitmap绘制到SurfaceViewint count = 100;Point p = null;while (count-- > 0) {p = getNextPoint();if (p == null) {//如果p为空，说明所有的点已经绘制完成return false;}mTmpCanvas.drawPoint(p.x, p.y + offsetY, mPaint);}//将bitmap绘制到SurfaceView中Canvas canvas = mSurfaceHolder.lockCanvas();canvas.drawBitmap(mTmpBm, 0, 0, mPaint);if (p != null)canvas.drawBitmap(mPaintBm, p.x, p.y - mPaintBm.getHeight() + offsetY, mPaint);mSurfaceHolder.unlockCanvasAndPost(canvas);return true;}

基本上绘制算完成了，附上完整的代码：

package com.hc.myoutline;import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Point;
import android.util.AttributeSet;
import android.view.SurfaceHolder;
import android.view.SurfaceView;/*** Package com.hc.myoutline* Created by HuaChao on 2016/5/27.*/
public class DrawOutlineView extends SurfaceView implements SurfaceHolder.Callback {private SurfaceHolder mSurfaceHolder;private Bitmap mTmpBm;private Canvas mTmpCanvas;private int mWidth;private int mHeight;private Paint mPaint;private int mSrcBmWidth;private int mSrcBmHeight;private boolean[][] mArray;private int offsetY = 100;private Bitmap mPaintBm;private Point mLastPoint = new Point(0, 0);public DrawOutlineView(Context context) {super(context);init();}public DrawOutlineView(Context context, AttributeSet attrs) {super(context, attrs);init();}private void init() {mSurfaceHolder = getHolder();mSurfaceHolder.addCallback(this);mPaint = new Paint();mPaint.setColor(Color.BLACK);}//设置画笔图片public void setPaintBm(Bitmap paintBm) {mPaintBm = paintBm;}//获取离指定点最近的一个未绘制过的点private Point getNearestPoint(Point p) {if (p == null) return null;//以点p为中心，向外扩大搜索范围，每次搜索的是与p点相距add的正方形for (int add = 1; add < mSrcBmWidth && add < mSrcBmHeight; add++) {//int beginX = (p.x - add) >= 0 ? (p.x - add) : 0;int endX = (p.x + add) < mSrcBmWidth ? (p.x + add) : mSrcBmWidth - 1;int beginY = (p.y - add) >= 0 ? (p.y - add) : 0;int endY = (p.y + add) < mSrcBmHeight ? (p.y + add) : mSrcBmHeight - 1;//搜索正方形的上下边for (int x = beginX; x <= endX; x++) {if (mArray[x][beginY]) {mArray[x][beginY] = false;return new Point(x, beginY);}if (mArray[x][endY]) {mArray[x][endY] = false;return new Point(x, endY);}}//搜索正方形的左右边for (int y = beginY + 1; y <= endY - 1; y++) {if (mArray[beginX][y]) {mArray[beginX][beginY] = false;return new Point(beginX, beginY);}if (mArray[endX][y]) {mArray[endX][y] = false;return new Point(endX, y);}}}return null;}//获取下一个需要绘制的点private Point getNextPoint() {mLastPoint = getNearestPoint(mLastPoint);return mLastPoint;}/*** //绘制* return :false 表示绘制完成，true表示还需要继续绘制*/private boolean draw() {mPaint.setStyle(Paint.Style.STROKE);mPaint.setColor(Color.BLACK);//获取count个点后，一次性绘制到bitmap在把bitmap绘制到SurfaceViewint count = 100;Point p = null;while (count-- > 0) {p = getNextPoint();if (p == null) {//如果p为空，说明所有的点已经绘制完成return false;}mTmpCanvas.drawPoint(p.x, p.y + offsetY, mPaint);}//将bitmap绘制到SurfaceView中Canvas canvas = mSurfaceHolder.lockCanvas();canvas.drawBitmap(mTmpBm, 0, 0, mPaint);if (p != null)canvas.drawBitmap(mPaintBm, p.x, p.y - mPaintBm.getHeight() + offsetY, mPaint);mSurfaceHolder.unlockCanvasAndPost(canvas);return true;}//重画public void reDraw(boolean[][] array) {if (isDrawing) return;mTmpBm = Bitmap.createBitmap(mWidth, mHeight, Bitmap.Config.ARGB_8888);mTmpCanvas = new Canvas(mTmpBm);mPaint.setColor(Color.WHITE);mPaint.setStyle(Paint.Style.FILL);mTmpCanvas.drawRect(0, 0, mWidth, mHeight, mPaint);mLastPoint = new Point(0, 0);beginDraw(array);}private boolean isDrawing = false;public void beginDraw(boolean[][] array) {if (isDrawing) return;this.mArray = array;mSrcBmWidth = array.length;mSrcBmHeight = array[0].length;new Thread() {@Overridepublic void run() {while (true) {isDrawing = true;boolean rs = draw();if (!rs) break;try {sleep(20);} catch (InterruptedException e) {e.printStackTrace();}}isDrawing = false;}}.start();}@Overridepublic void surfaceCreated(SurfaceHolder holder) {}@Overridepublic void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {this.mWidth = width;this.mHeight = height;mTmpBm = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);mTmpCanvas = new Canvas(mTmpBm);mPaint.setColor(Color.WHITE);mPaint.setStyle(Paint.Style.FILL);mTmpCanvas.drawRect(0, 0, mWidth, mHeight, mPaint);Canvas canvas = holder.lockCanvas();canvas.drawBitmap(mTmpBm, 0, 0, mPaint);holder.unlockCanvasAndPost(canvas);mPaint.setStyle(Paint.Style.STROKE);}@Overridepublic void surfaceDestroyed(SurfaceHolder holder) {}
}

接下来是在MainActivity里面传入参数过来，附上MainActivity的代码：

package com.hc.myoutline;import android.graphics.Bitmap;
import android.graphics.Color;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.MotionEvent;public class MainActivity extends AppCompatActivity {private DrawOutlineView drawOutlineView;private Bitmap sobelBm;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);//将Bitmap压缩处理，防止OOMBitmap bm = CommenUtils.getRatioBitmap(this, R.drawable.test, 100, 100);//返回的是处理过的BitmapsobelBm = SobelUtils.Sobel(bm);drawOutlineView = (DrawOutlineView) findViewById(R.id.outline);Bitmap paintBm = CommenUtils.getRatioBitmap(this, R.drawable.paint, 10, 20);drawOutlineView.setPaintBm(paintBm);}//根据Bitmap信息，获取每个位置的像素点是否需要绘制//使用boolean数组而不是int[][]主要是考虑到内存的消耗private boolean[][] getArray(Bitmap bitmap) {boolean[][] b = new boolean[bitmap.getWidth()][bitmap.getHeight()];for (int i = 0; i < bitmap.getWidth(); i++) {for (int j = 0; j < bitmap.getHeight(); j++) {if (bitmap.getPixel(i, j) != Color.WHITE)b[i][j] = true;elseb[i][j] = false;}}return b;}boolean first = true;//点击时开始绘制@Overridepublic boolean onTouchEvent(MotionEvent event) {if (first) {first = false;drawOutlineView.beginDraw(getArray(sobelBm));} elsedrawOutlineView.reDraw(getArray(sobelBm));return true;}
}