Android贝塞尔曲线——曲线进阶

本文同步自我的CSDN：http://blog.csdn.net/rubeson/article/details/54670792

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！

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！

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。

这个样子我能做出来你们也一定可以哦，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。

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。