本文在我的CSDN同步发布，Android贝塞尔曲线——曲线进阶
Hello，大家好，今天我的题目是Android贝塞尔曲线——曲线进阶，那么为什么叫做进阶呢？那当然是之前我写过初级的内容咯，没有读过的小伙伴可以点击Android贝塞尔曲线——曲线初体验来进行查看。
今天来进阶一下曲线，上次我为大家带来的是贝塞尔曲线的初级实现，也就是二阶贝塞尔曲线，今天我想为大家说一下三阶贝塞尔曲线，其实也是非常简单的。我的目标是为大家带来最干的货。辣么，我们开始吧！
什么是贝塞尔三阶？##
那么有人要问了，什么是贝塞尔三阶曲线呢，他与二阶曲线有什么不同？我也不知道这个有人是哪位，不过他问的问题总是这么的犀利。。那么我来回答一下。众所周知，贝塞尔曲线二阶是由一个起点、一个控制点、一个终点来构成，那么三阶自然就是多出了一个控制点。 文字总是这么苍白无力，还是来看图吧！
三阶贝塞尔曲线
上图就是三阶贝塞尔曲线的基本形态，是不是比二阶多出了一个控制点。那么我们继续来看一下它的动态绘制过程吧！
动态贝塞尔三阶曲线
可见，三阶贝塞尔曲线从P0点经过P1、P2两个控制点最后到P3的终点完成了这条曲线的绘制。
撸码时间##
那么我们开始正式的撸码，首先创建一个BezierThiredView 让他继承View，如我下面的代码。
public class BezierThiredView extends View {
// 开始坐标
private float startXPoint;
private float startYPoint;
// 结束坐标
private float endXPoint;
private float endYPoint;
// 两个控制点
private float conOneXPoint;
private float conOneYPoint;
private float conTwoXPoint;
private float conTwoYPoint;
// 画笔、路径
private Path mPath;
private Paint mPaint;
private Paint mPaintCon;
private Paint mPaintText;
public BezierThiredView(Context context) {
super(context);
}
public BezierThiredView(Context context, AttributeSet attrs) {
super(context, attrs);
mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setColor(Color.RED);
mPaint.setStrokeWidth(8);
mPaintCon = new Paint(Paint.ANTI_ALIAS_FLAG);
mPaintCon.setStyle(Paint.Style.STROKE);
mPaintCon.setStrokeWidth(3);
mPaintText = new Paint(Paint.ANTI_ALIAS_FLAG);
mPaintText.setStyle(Paint.Style.STROKE);
mPaintText.setTextSize(20);
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
startXPoint = w / 4;
startYPoint = h / 2;
endXPoint = w * 3 / 4;
endYPoint = h / 2;
conOneXPoint = w / 2 - 100;
conOneYPoint = h / 2 - 400;
conTwoXPoint = w / 2 + 100;
conTwoYPoint = h / 2 - 400;
mPath = new Path();
}
public BezierThiredView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
mPath.reset();
mPath.moveTo(startXPoint,startYPoint);
mPath.cubicTo(conOneXPoint,conOneYPoint,conTwoXPoint,conTwoYPoint,endXPoint,endYPoint);
canvas.drawPoint(startXPoint,startYPoint,mPaintCon);
canvas.drawText("P0",startXPoint-50,startYPoint,mPaintText);
canvas.drawPoint(endXPoint,endYPoint,mPaintCon);
canvas.drawText("P3",endXPoint+50,endYPoint,mPaintText);
canvas.drawPoint(conOneXPoint, conOneYPoint,mPaintCon);
canvas.drawText("P1", conOneXPoint-50, conOneYPoint,mPaintText);
canvas.drawPoint(conTwoXPoint, conTwoYPoint,mPaintCon);
canvas.drawText("P2", conTwoXPoint+50, conTwoYPoint,mPaintText);
canvas.drawLine(startXPoint,startYPoint, conOneXPoint, conOneYPoint,mPaintCon);
canvas.drawLine(conOneXPoint, conOneYPoint,conTwoXPoint,conTwoYPoint,mPaintCon);
canvas.drawLine(conTwoXPoint, conTwoYPoint,endXPoint,endYPoint,mPaintCon);
canvas.drawPath(mPath,mPaint);
}
}
跟着我上面代码就可以画出一条三阶贝塞尔曲线，其中path.cubicTo是系统提供给我们绘制三阶曲线的专用方法，我们来把他放到布局中来运行一下看看效果，这里我就省略添加自定义view到布局这段代码了。
三阶贝塞尔曲线效果图
这个样子我能做出来你们也一定可以哦，Duang！
duang
为了节省篇幅我也把辅助线一并画出来，下面我要带大家实现一下拖拽效果。
废话不说了，直接上代码!
public class BezierThiredView extends View {
// 开始坐标
private float startXPoint;
private float startYPoint;
// 结束坐标
private float endXPoint;
private float endYPoint;
// 两个控制点
private float conOneXPoint;
private float conOneYPoint;
private float conTwoXPoint;
private float conTwoYPoint;
// 画笔、路径
private Path mPath;
private Paint mPaint;
private Paint mPaintCon;
private Paint mPaintText;
private boolean isPointDown; // 手指是否按下
public BezierThiredView(Context context) {
super(context);
}
public BezierThiredView(Context context, AttributeSet attrs) {
super(context, attrs);
mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setColor(Color.RED);
mPaint.setStrokeWidth(8);
mPaintCon = new Paint(Paint.ANTI_ALIAS_FLAG);
mPaintCon.setStyle(Paint.Style.STROKE);
mPaintCon.setStrokeWidth(3);
mPaintText = new Paint(Paint.ANTI_ALIAS_FLAG);
mPaintText.setStyle(Paint.Style.STROKE);
mPaintText.setTextSize(20);
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
startXPoint = w / 4;
startYPoint = h / 2;
endXPoint = w * 3 / 4;
endYPoint = h / 2;
conOneXPoint = w / 2 - 100;
conOneYPoint = h / 2 - 400;
conTwoXPoint = w / 2 + 100;
conTwoYPoint = h / 2 - 400;
mPath = new Path();
}
public BezierThiredView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
mPath.reset();
mPath.moveTo(startXPoint,startYPoint);
mPath.cubicTo(conOneXPoint,conOneYPoint,conTwoXPoint,conTwoYPoint,endXPoint,endYPoint);
canvas.drawPoint(startXPoint,startYPoint,mPaintCon);
canvas.drawText("P0",startXPoint-50,startYPoint,mPaintText);
canvas.drawPoint(endXPoint,endYPoint,mPaintCon);
canvas.drawText("P3",endXPoint+50,endYPoint,mPaintText);
canvas.drawPoint(conOneXPoint, conOneYPoint,mPaintCon);
canvas.drawText("P1", conOneXPoint-50, conOneYPoint,mPaintText);
canvas.drawPoint(conTwoXPoint, conTwoYPoint,mPaintCon);
canvas.drawText("P2", conTwoXPoint+50, conTwoYPoint,mPaintText);
canvas.drawLine(startXPoint,startYPoint, conOneXPoint, conOneYPoint,mPaintCon);
canvas.drawLine(conOneXPoint, conOneYPoint,conTwoXPoint,conTwoYPoint,mPaintCon);
canvas.drawLine(conTwoXPoint, conTwoYPoint,endXPoint,endYPoint,mPaintCon);
canvas.drawPath(mPath,mPaint);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
switch (event.getAction() & MotionEvent.ACTION_MASK) {
case MotionEvent.ACTION_POINTER_DOWN:
isPointDown = true;
break;
case MotionEvent.ACTION_POINTER_UP:
isPointDown = false;
break;
case MotionEvent.ACTION_MOVE:
conOneXPoint = event.getX(0);
conOneYPoint = event.getY(0);
if (isPointDown) {
conTwoXPoint = event.getX(1);
conTwoYPoint = event.getY(1);
}
invalidate();
break;
}
return true;
}
}
我们两个手指一起操作来对贝塞尔三阶曲线进行各种男人的撕扯吧！我不知道使用什么东西来录制屏幕，只能给大家上一张经过我拉扯后的图。
贝塞尔曲线图
好了，这次这篇就到这里吧，请大家继续关注我，以后还会去更新贝塞尔曲线的文章。
题外话：如果谁知道用什么软件可以录制手机屏幕并生成gif图的可以在下方留言。 哈哈，好的我们下期再见。
