Android如何用手指画一条平滑的线

Android如何用手指画一条平滑的线

正如你提到的，一个简单的解决方案是简单地将点与直线连接起来。这是这样做的代码：

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);}

确保将油漆从填充更改为描边：

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

另一个选择是使用quadTo方法将点与迭代连接：

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);}

这仍然会导致一些尖锐的边缘。

如果你确实有野心，则可以开始如下计算三次样条：

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，我发现你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);}

并将dx和dy值添加到Point类：

class Point {    float x, y;    float dx, dy;    @Override    public String toString() {        return x + ", " + y;    }}

这样可以产生平滑的线条，但有时必须使用循环将点连接起来。另外，对于较长的绘图会话，这将需要大量计算才能计算。

希望对你有所帮助。