RotateCTM使图形消失，Quartz 2D
首先，我是一个石英 2d 菜鸟。我有一个饼图，基本上想在东北象限中对角线画一条线，然后水平向右，并有一个标签解释该部分是什么。所以，我有这段绘制对角线的代码。该线向东南延伸。我预计这是基于 iPhone 的原产地位于西北象限。所以我想我可以先将我的 CTM 旋转 3pi/2，然后让相同的代码工作。但是，当我取消注释 CGContextRotateCTM() 行时，我没有得到任何行。我不确定这里发生了什么以及逻辑错误在哪里。谢谢。
CGPoint circleCenter = CGPointMake(self.bounds.size.width / 2, self.bounds.size.height / 2);
CGContextSetFillColorWithColor(context, [[UIColor whiteColor] CGColor]);
CGContextSetRGBStrokeColor(context, 1.0, 1.0, 1.0, 1.0);
CGContextSetLineWidth(context, LINE_WIDTH);
CGContextBeginPath(context);
// CGContextRotateCTM(context, 3 * M_PI / 2);
CGContextMoveToPoint(context, circleCenter.x + self.CircleRadius / 2, circleCenter.y + self.CircleRadius / 2);
CGContextAddLineToPoint(context, circleCenter.x + self.CircleRadius / 2 + LINE_LENGTH, circleCenter.y + self.CircleRadius / 2 + LINE_LENGTH);
CGContextStrokePath(context);
First off, I am a quartz 2d noob. I have a pie chart, and basically want to make a line coming out of it diagonally, in the northeast quadrant, then go horizontal to the right, and have a label explaining what that section is. So, I have this code that draws the diagonal line. The line draws to the southeast. I expect that based on the iPhone origin being in the northwest quadrant. So I thought I could rotate my CTM first by 3pi/2, and then have that same code work. However, when I uncomment the CGContextRotateCTM() line, I get no line. I'm not sure what is happening here and where the logic error is. Thanks.
CGPoint circleCenter = CGPointMake(self.bounds.size.width / 2, self.bounds.size.height / 2);
CGContextSetFillColorWithColor(context, [[UIColor whiteColor] CGColor]);
CGContextSetRGBStrokeColor(context, 1.0, 1.0, 1.0, 1.0);
CGContextSetLineWidth(context, LINE_WIDTH);
CGContextBeginPath(context);
// CGContextRotateCTM(context, 3 * M_PI / 2);
CGContextMoveToPoint(context, circleCenter.x + self.CircleRadius / 2, circleCenter.y + self.CircleRadius / 2);
CGContextAddLineToPoint(context, circleCenter.x + self.CircleRadius / 2 + LINE_LENGTH, circleCenter.y + self.CircleRadius / 2 + LINE_LENGTH);
CGContextStrokePath(context);
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似乎您正在将线路旋转到视线之外。始终牢记您旋转的中心 - 也许还可以先翻译您的 CTM。
编辑：要进行检查，您可能需要逐步尝试非常小的旋转并观察您的线的走向。
It seems you are rotating your line out of sight. Always keep the center in mind that you rotate around - maybe also translate your CTM first.
Edit: To check, you might want to try very small rotations incrementally and watch where your line goes.