android - 在 Android Canvas 上绘图，角度不正确

Question

我有一个为 Android 创建的自定义 View ，我在其中绘制一个圆并将其分成几个部分。

这是 onDraw 的代码:

int w = Width;
int h = Height;

int pl = PaddingLeft;
int pr = PaddingRight;
int pt = PaddingTop;
int pb = PaddingBottom;

int usableWidth = w - (pl + pr);
int usableHeight = h - (pt + pb);

int radius = Math.Min(usableWidth, usableHeight) / 2;
int cx = pl + (usableWidth / 2);
int cy = pt + (usableHeight / 2);

int lineLenght = radius - (pl * 2) - (pr * 2);

paint.Color = Color.Black;
paint.SetStyle(Paint.Style.Stroke);
canvas.DrawCircle(cx, cy, radius, paint);

//Move to top of the circle
float pointAngle = 360 / noOfJoints;
for (float angle = 0; angle < 361; angle = angle + pointAngle)
{   //move round the circle to each point
    float x = cx + ((float)Math.Cos(radians(angle)) * radius); //convert angle to radians for x and y coordinates
    float y = cy + ((float)Math.Sin(radians(angle)) * radius);
    canvas.DrawLine(cx, cy, x, y, paint); //draw a line from center point back to the point
}

但是当我运行它时，它会提供如下 View :

这接近我想要的，但部分的开始应该从中间开始。我怎样才能让它从 0 角度开始(第一个分隔线应该是从上到下的直线)。

首选圈子如下:

Answer 1

试试这个:

for (float angle = 0; angle < 361; angle = angle + pointAngle)
{   //move round the circle to each point
    float displacedAngle = angle - 90;
    float x = cx + ((float)Math.Cos(radians(displacedAngle)) * radius); //convert angle to radians for x and y coordinates
    float y = cy + ((float)Math.Sin(radians(displacedAngle)) * radius);
    canvas.DrawLine(cx, cy, x, y, paint); //draw a line from center point back to the point
}

角度0是圆最右边的点，减去90就是圆的顶点。

另外，一个建议，尽量避免在onDraw方法中创建变量和实例化对象。这是一个真正的性能 killer 。