绘制线的坐标

Question

我在屏幕的中间画了一个圆，我想从圆的中心向上向下绘制四条线a，向左和向右 ，问题是我绘制的链接我不能确定它们的长度

@Override 
protected void onDraw (Canvas canvas){ 
    super.onDraw(canvas); 
    int x = getWidth(); 
    int y = getHeight(); 
    int radius; 
    radius = 25; 
    Paint paint = new Paint() ; 
    paint.setStyle(Paint.Style.FILL); 
    paint.setColor(Color.BLACK); 
    canvas.drawPaint(paint); 
    paint.setColor(Color.WHITE); 
    canvas.drawCircle(x/2, y/2, radius, paint); 
    Paint paint1 = new Paint() ; 
    paint1.setStyle(Paint.Style.FILL); 
    paint1.setColor(Color.BLACK); 
    canvas.drawPaint(paint1); 
    paint1.setColor(Color.WHITE); 
    canvas.drawLine(x/2, y/2, x, y/2, paint1); 
    canvas.drawLine(x/2, y/2, -x, y/2, paint1); 
    canvas.drawLine(x/2, y/2, x/2, y, paint1); 
    canvas.drawLine(x/2, y/2, x/2, -y, paint1); 
} 

Answer 1

所以，你要4线 - 两条对角线的，一个垂直和水平之一，所有过境通过圆心。

首先，让我们设置的圆心：

int centerX = x/2; 
int centerY = y/2; 

然后，添加一些辅助变量的左，上，右，下了线。我们加一点余量，这样会有余地额外的线路在对角线的两端：

int margin = 10; // Arbitrary value, modify as desired 
int top = 0 + margin; 
int bottom = canvas.getHeight() - margin; 
int left = 0 + margin; 
int right = canvas.getWidth() - margin; 

有了这些，我们可以绘制线条容易：

// Vertical line. X coordinate = center, stretching from "top" to "bottom" 
canvas.drawLine(centerX, top, centerX, bottom); 

// Horizontal line. Y coordinate = center, stretching from "left" to "right". 
canvas.drawLine(left, centerY, right, centerY); 

// First diagonal line. Stretching from the top left corner to the bottom right corner. 
canvas.drawLine(top, left, bottom, right); 

// Second diagonal line. Stretching from the top right corner to the bottom left corner. 
canvas.drawLine(top, right, bottom, left); 

现在加入小线段使它看起来像一个曲线：

int delta = 4; // Arbitrary value, determines how long the small lines will be. 
canvas.drawLine(top, left, top + delta, left - delta); 
canvas.drawLine(top, right, top + delta, right + delta); 
canvas.drawLine(bottom, left, bottom - delta, left - delta); 
canvas.drawLine(bottom, right, bottom - delta, right + delta); 

如果你想曲线是圆的，而不是尖锐的，你有两个选择。
首先是制作透明物体Image并将其放在画布上。您可以制作一条曲线的图像，并将其镜像以获取其他三条曲线。
第二个是使用Path.cubicTo，但这是你可能想要稍后尝试的东西。如果你想了解它，在this Stack Overflow answer中有详细解释。