Android 如何沿着手指画一条平滑的线

Question

http://marakana.com/tutorials/android/2d-graphics-example.html

我我正在使用下面这个例子。但当我在屏幕上移动手指太快时，线条就会变成单独的点。

我不确定是否可以加快绘图速度。或者我应该用直线连接最后两个点。这两个解决方案中的第二个似乎是一个不错的选择，除非当您快速移动手指时，您将看到很长的直线部分，然后是尖锐的曲线。

如果还有其他解决方案，很高兴听到它们。

感谢您提前提供的任何帮助。

Answer 1

正如您提到的，一个简单的解决方案就是简单地用直线连接这些点。以下是执行此操作的代码：

public void onDraw(Canvas canvas) {
    Path path = new Path();
    boolean first = true;
    for(Point point : points){
        if(first){
            first = false;
            path.moveTo(point.x, point.y);
        }
        else{
            path.lineTo(point.x, point.y);
        }
    }
    canvas.drawPath(path, paint);
}

确保将绘画从填充更改为描边：

paint = new Paint(Paint.ANTI_ALIAS_FLAG);
paint.setStyle(Paint.Style.STROKE);
paint.setStrokeWidth(2);
paint.setColor(Color.WHITE);

另一个选项是使用quadTo方法通过迭代连接点：

public void onDraw(Canvas canvas) {
    Path path = new Path();
    boolean first = true;
    for(int i = 0; i < points.size(); i += 2){
        Point point = points.get(i);
        if(first){
            first = false;
            path.moveTo(point.x, point.y);
        }

        else if(i < points.size() - 1){
            Point next = points.get(i + 1);
            path.quadTo(point.x, point.y, next.x, next.y);
        }
        else{
            path.lineTo(point.x, point.y);
        }
    }

    canvas.drawPath(path, paint);
}

这仍然会产生一些尖锐的边缘。

如果您真的雄心勃勃，您可以开始计算三次样条，如下所示：

public void onDraw(Canvas canvas) {
    Path path = new Path();

    if(points.size() > 1){
        for(int i = points.size() - 2; i < points.size(); i++){
            if(i >= 0){
                Point point = points.get(i);

                if(i == 0){
                    Point next = points.get(i + 1);
                    point.dx = ((next.x - point.x) / 3);
                    point.dy = ((next.y - point.y) / 3);
                }
                else if(i == points.size() - 1){
                    Point prev = points.get(i - 1);
                    point.dx = ((point.x - prev.x) / 3);
                    point.dy = ((point.y - prev.y) / 3);
                }
                else{
                    Point next = points.get(i + 1);
                    Point prev = points.get(i - 1);
                    point.dx = ((next.x - prev.x) / 3);
                    point.dy = ((next.y - prev.y) / 3);
                }
            }
        }
    }

    boolean first = true;
    for(int i = 0; i < points.size(); i++){
        Point point = points.get(i);
        if(first){
            first = false;
            path.moveTo(point.x, point.y);
        }
        else{
            Point prev = points.get(i - 1);
            path.cubicTo(prev.x + prev.dx, prev.y + prev.dy, point.x - point.dx, point.y - point.dy, point.x, point.y);
        }
    }
    canvas.drawPath(path, paint);
}

另外，我发现您需要更改以下内容以避免重复的运动事件：

public boolean onTouch(View view, MotionEvent event) {
    if(event.getAction() != MotionEvent.ACTION_UP){
        Point point = new Point();
        point.x = event.getX();
        point.y = event.getY();
        points.add(point);
        invalidate();
        Log.d(TAG, "point: " + point);
        return true;
    }
    return super.onTouchEvent(event);
}

并添加 dx 和 dx 。 dy 值传递给 Point 类：

class Point {
    float x, y;
    float dx, dy;

    @Override
    public String toString() {
        return x + ", " + y;
    }
}

这会产生平滑的线条，但有时必须使用循环连接点。
此外，对于长时间的绘图会话，这会变得计算量很大。

编辑

我整理了一个快速项目来演示这些不同的技术，包括 Square 建议的签名实现。享受：https://github.com/johncarl81/androiddraw

Answer 2

这对你来说可能不再重要，但我花了很多功夫才解决它，我想分享，可能对其他人有用。

@johncarl 提供的解决方案教程非常适合绘图，但它们对我的目的提供了限制。如果您将手指从屏幕上移开并放回去，此解决方案将在上次单击和新单击之间画一条线，使整个绘图始终连接。所以我试图找到一个解决方案，最后我得到了它！（抱歉，如果听起来很明显，我是图形初学者）

public class MainActivity extends Activity {
    DrawView drawView;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // Set full screen view
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
                     WindowManager.LayoutParams.FLAG_FULLSCREEN);
        requestWindowFeature(Window.FEATURE_NO_TITLE);

        drawView = new DrawView(this);
        setContentView(drawView);
        drawView.requestFocus();
    }
}


public class DrawingPanel extends View implements OnTouchListener {
    private static final String TAG = "DrawView";

    private static final float MINP = 0.25f;
    private static final float MAXP = 0.75f;

    private Canvas  mCanvas;
    private Path    mPath;
    private Paint       mPaint;   
    private LinkedList<Path> paths = new LinkedList<Path>();

    public DrawingPanel(Context context) {
        super(context);
        setFocusable(true);
        setFocusableInTouchMode(true);

        this.setOnTouchListener(this);

        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setDither(true);
        mPaint.setColor(Color.BLACK);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeJoin(Paint.Join.ROUND);
        mPaint.setStrokeCap(Paint.Cap.ROUND);
        mPaint.setStrokeWidth(6);
        mCanvas = new Canvas();
        mPath = new Path();
        paths.add(mPath);
    }               

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
    }

    @Override
    protected void onDraw(Canvas canvas) {            
        for (Path p : paths){
            canvas.drawPath(p, mPaint);
        }
    }

    private float mX, mY;
    private static final float TOUCH_TOLERANCE = 4;

    private void touch_start(float x, float y) {
        mPath.reset();
        mPath.moveTo(x, y);
        mX = x;
        mY = y;
    }

    private void touch_move(float x, float y) {
        float dx = Math.abs(x - mX);
        float dy = Math.abs(y - mY);
        if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
            mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
            mX = x;
            mY = y;
        }
    }

    private void touch_up() {
        mPath.lineTo(mX, mY);
        // commit the path to our offscreen
        mCanvas.drawPath(mPath, mPaint);
        // kill this so we don't double draw            
        mPath = new Path();
        paths.add(mPath);
    }

    @Override
    public boolean onTouch(View arg0, MotionEvent event) {
        float x = event.getX();
        float y = event.getY();

        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                touch_start(x, y);
                invalidate();
                break;
            case MotionEvent.ACTION_MOVE:
                touch_move(x, y);
                invalidate();
                break;
            case MotionEvent.ACTION_UP:
                touch_up();
                invalidate();
                break;
        }
        return true;
    } 
}  

我用手指绘制了android示例，并对其进行了一些修改以存储每个路径仅最后一个！希望它能帮助别人！

干杯。

Answer 3

我尝试了几种方法来渲染运动事件的累积点。
最后，我通过计算两点之间的中点并将列表中的点视为二次贝塞尔曲线的锚点（除了第一个和最后一个点，它们通过简单的线连接到下一个中​​点）得到了最好的结果）。

这给出了没有任何拐角的平滑曲线。绘制的路径不会接触列表中的实际点，而是经过每个中点。

Path path = new Path();
if (points.size() > 1) {
    Point prevPoint = null;
    for (int i = 0; i < points.size(); i++) {
        Point point = points.get(i);

        if (i == 0) {
            path.moveTo(point.x, point.y);
        } else {
            float midX = (prevPoint.x + point.x) / 2;
            float midY = (prevPoint.y + point.y) / 2;

            if (i == 1) {
                path.lineTo(midX, midY);
            } else {
                path.quadTo(prevPoint.x, prevPoint.y, midX, midY);
            }
        }
        prevPoint = point;
    }
    path.lineTo(prevPoint.x, prevPoint.y);
}

Answer 4

如果您想要简单一点：

public class DrawByFingerCanvas extends View {

    private Paint brush = new Paint(Paint.ANTI_ALIAS_FLAG);
    private Path path = new Path();

    public DrawByFingerCanvas(Context context) {
        super(context);
        brush.setStyle(Paint.Style.STROKE);
        brush.setStrokeWidth(5);
    }

    @Override
    protected void onDraw(Canvas c) {
        c.drawPath(path, brush);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {

        float x = event.getX();
        float y = event.getY();

        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                path.moveTo(x,y);
                break;
            case MotionEvent.ACTION_MOVE:
                path.lineTo(x, y);
                break;
            default:
                return false;
        }
        invalidate();
        return true;
    }
}

在活动中只需：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(new DrawByFingerCanvas(this));
}

结果：

要删除所有绘图，只需旋转屏幕即可。

Answer 5

我有非常类似的问题。当您调用 onTouch 方法时，您还应该使用方法（在 onTouch(MotionEvent event) 内部）

event.getHistorySize();

和
类似的东西

int histPointsAmount = event.getHistorySize(); 
for(int i = 0; i < histPointsAmount; i++){
    // get points from event.getHistoricalX(i);
    // event.getHistoricalY(i); and use them for your purpouse
}

Answer 6

具有 ACTION_MOVE 的运动事件可以将单个对象内的多个运动样本批量处理在一起。使用 getX(int) 和 getY(int) 可以获得最新的指针坐标。使用 getHistoricalX(int, int) 和 getHistoricalY(int, int) 访问批次中较早的坐标。使用它们来构建路径使其更加平滑：

    int historySize = event.getHistorySize();
    for (int i = 0; i < historySize; i++) {
      float historicalX = event.getHistoricalX(i);
      float historicalY = event.getHistoricalY(i);
      path.lineTo(historicalX, historicalY);
    }

    // After replaying history, connect the line to the touch point.
    path.lineTo(eventX, eventY);

这是来自 Square 的一个很好的教程：http://corner.squareup.com/2010/07/smooth-signatures.html

Answer 7

我最近不得不对此进行一些修改，现在已经开发出我认为是最好的解决方案，因为它做了三件事：

1. 它允许您绘制不同的线条
2. 它适用于较大的笔触，并且无需使用复杂的三次样条
3. 它是比这里的许多解决方案更快，因为 canvas.drawPath() 方法位于 for 循环外部，因此不会多次调用它。

---

public class DrawView extends View implements OnTouchListener {
private static final String TAG = "DrawView";

List<Point> points = new ArrayList<Point>();
Paint paint = new Paint();
List<Integer> newLine = new ArrayList<Integer>();

public DrawView(Context context, AttributeSet attrs){
        super(context, attrs);
        setFocusable(true);
        setFocusableInTouchMode(true);
        setClickable(true);

        this.setOnTouchListener(this);

        paint.setColor(Color.WHITE);
        paint.setAntiAlias(true);
        paint.setStyle(Paint.Style.STROKE);
        paint.setStrokeWidth(20);

    }

    public void setColor(int color){
        paint.setColor(color);
    }
    public void setBrushSize(int size){
        paint.setStrokeWidth((float)size);
    }
    public DrawView(Context context) {
        super(context);
        setFocusable(true);
        setFocusableInTouchMode(true);

        this.setOnTouchListener(this);


        paint.setColor(Color.BLUE);
        paint.setAntiAlias(true);
        paint.setStyle(Paint.Style.STROKE);
        paint.setStrokeWidth(20);
    }

    @Override
    public void onDraw(Canvas canvas) {
        Path path = new Path();
        path.setFillType(Path.FillType.EVEN_ODD);
        for (int i = 0; i<points.size(); i++) {
            Point newPoint = new Point();
            if (newLine.contains(i)||i==0){
                newPoint = points.get(i)
                path.moveTo(newPoint.x, newPoint.y);
            } else {
                newPoint = points.get(i);

                path.lineTo(newPoint.x, newPoint.y);
            }

        }
        canvas.drawPath(path, paint);
    }

    public boolean onTouch(View view, MotionEvent event) {
        Point point = new Point();
        point.x = event.getX();
        point.y = event.getY();
        points.add(point);
        invalidate();
        Log.d(TAG, "point: " + point);
        if(event.getAction() == MotionEvent.ACTION_UP){
            // return super.onTouchEvent(event);
            newLine.add(points.size());
        }
        return true;
    }
    }

    class Point {
        float x, y;

    @Override
    public String toString() {
        return x + ", " + y;
    }
    }

这也有效，只是不太好

  import java.util.ArrayList;
import java.util.List;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.util.*;

public class DrawView extends View implements OnTouchListener {
    private static final String TAG = "DrawView";
List<Point> points = new ArrayList<Point>();
Paint paint = new Paint();
List<Integer> newLine = new ArrayList<Integer>();

public DrawView(Context context, AttributeSet attrs){
    super(context, attrs);
    setFocusable(true);
    setFocusableInTouchMode(true);

    this.setOnTouchListener(this);

    paint.setColor(Color.WHITE);
    paint.setAntiAlias(true);
}
public DrawView(Context context) {
    super(context);
    setFocusable(true);
    setFocusableInTouchMode(true);

    this.setOnTouchListener(this);

    paint.setColor(Color.WHITE);
    paint.setAntiAlias(true);
    }

@Override
public void onDraw(Canvas canvas) {
    for (int i = 0; i<points.size(); i++) {
        Point newPoint = new Point();
        Point oldPoint = new Point();
        if (newLine.contains(i)||i==0){
            newPoint = points.get(i);
            oldPoint = newPoint;
        } else {
            newPoint = points.get(i);
            oldPoint = points.get(i-1);
        }
            canvas.drawLine(oldPoint.x, oldPoint.y, newPoint.x, newPoint.y, paint);
    }
}

public boolean onTouch(View view, MotionEvent event) {
    Point point = new Point();
    point.x = event.getX();
    point.y = event.getY();
    points.add(point);
    invalidate();
    Log.d(TAG, "point: " + point);
    if(event.getAction() == MotionEvent.ACTION_UP){
        // return super.onTouchEvent(event);
        newLine.add(points.size());
    }
    return true;
    }
}

class Point {
    float x, y;

    @Override
    public String toString() {
        return x + ", " + y;
    }
}

它可以让你很好地绘制线条，唯一的问题是如果你使线条变粗，这会使绘制的线条看起来有点奇怪，而且实际上，我还是建议使用第一个。

Answer 8

您的 MotionEvent 中的可用信息可能比您意识到的多得多，可以在中间提供一些数据。

您链接中的示例忽略了事件中包含的历史接触点。请参阅 MotionEvent 文档顶部附近的“批处理”部分：http://developer.android.com/reference/android/view/MotionEvent.html 除此之外，用线连接点可能不是一个坏主意。

Answer 9

这是一个简化的解决方案，可以沿着手指画一条线并且始终是直的：

https://stackoverflow.com/a/68076519/ 15463816

Answer 10

我遇到了这个问题，我画的是点而不是线。您应该首先创建一条路径来保持阵地。仅在第一次触摸事件时调用 path.moveto 。然后在画布上绘制路径，然后在完成后重置或倒带路径（path.reset）...

Answer 11

这是一个平滑 Path 绘制的点的简单方法。行至

fun applySmoothing(smoothingIterations: Int) {
    for (z in 1..smoothingIterations) {
        for (i in graphPoints.indices) {
            if (i > 0 && i < graphPoints.size-1) {
                val previousPoint = graphPoints[i-1]
                val currentPoint = graphPoints[i]
                val nextPoint = graphPoints[i+1]
                val midX = (previousPoint.x + currentPoint.x + nextPoint.x) / 3
                val midY = (previousPoint.y + currentPoint.y + nextPoint.y) / 3
                graphPoints[i].x = midX
                graphPoints[i].y = midY
            }
        }
    }
}