如何在Objective-C中获得CGContext的最后一点？

Question

我正在研究自定义进度条，我想得到CGContext的最后一点，因为我想将图像添加到当前状态。

这是我的代码：

-(void)drawRect:(CGRect)rect {
CGContextRef ctx = UIGraphicsGetCurrentContext();

CGPoint center = CGPointMake(rect.size.width/2, rect.size.height/2);
float minSize = MIN(rect.size.width, rect.size.height);
float lineWidth = _strokeWidth;
if(lineWidth == -1.0) lineWidth = minSize*_strokeWidthRatio;
float radius = (minSize-lineWidth)/2;
float endAngle = M_PI*(self.value*2);

//what should i do here
//_pont.center = CGPointMake

CGContextSaveGState(ctx);
CGContextTranslateCTM(ctx, center.x, center.y);
CGContextRotateCTM(ctx, -M_PI*0.5);


CGContextSetLineWidth(ctx, lineWidth);
CGContextSetLineCap(ctx, kCGLineCapRound);

// "Full" Background Circle:
CGContextBeginPath(ctx);
CGContextAddArc(ctx, 0, 0, radius, 0, 2*M_PI, 0);
CGContextSetStrokeColorWithColor(ctx, [_color colorWithAlphaComponent:0.1].CGColor);
CGContextStrokePath(ctx);

// Progress Arc:
CGContextBeginPath(ctx);
CGContextAddArc(ctx, 0, 0, radius, 0, endAngle, 0);
CGContextSetStrokeColorWithColor(ctx, [_color colorWithAlphaComponent:0.9].CGColor);
CGContextStrokePath(ctx);

CGContextRestoreGState(ctx);
}

Answer 1

您必须使用CGContextGetPathCurrentPoint，但必须在通过调用stroke或fill清除路径之前调用它。 因此，请查看以下操场，并查看CGContextGetPathCurrentPoint返回的值在调用时的变化。

import CoreGraphics
import UIKit

let lineWidth = CGFloat(10)
let rect = CGRectMake(0, 0, 100, 100)
let size = CGSizeMake(100, 100)
UIGraphicsBeginImageContextWithOptions(size, false, 0.0)
let ctx = UIGraphicsGetCurrentContext()

let center = CGPointMake(rect.size.width/2, rect.size.height/2);
let minSize = fmin(rect.size.width, rect.size.height);

let radius = (minSize-10)/2;
let endAngle = CGFloat(M_PI*(20.0*2))

CGContextSaveGState(ctx);
CGContextTranslateCTM(ctx, center.x, center.y);
CGContextRotateCTM(ctx, CGFloat(-M_PI*0.5));


CGContextSetLineWidth(ctx, lineWidth);
CGContextSetLineCap(ctx, CGLineCap.Round);

// "Full" Background Circle:
CGContextBeginPath(ctx);
CGContextAddArc(ctx, 0, 0, radius, 0, CGFloat(2*M_PI), 0);
CGContextSetStrokeColorWithColor(ctx, UIColor.greenColor().CGColor);
var  endPoint = CGContextGetPathCurrentPoint(ctx)
CGContextStrokePath(ctx);
endPoint = CGContextGetPathCurrentPoint(ctx)

// Progress Arc:
CGContextBeginPath(ctx);
CGContextAddArc(ctx, 0, 0, radius, 0, endAngle, 0);
endPoint = CGContextGetPathCurrentPoint(ctx)
CGContextSetStrokeColorWithColor(ctx, UIColor.redColor().CGColor);
CGContextStrokePath(ctx);


CGContextRestoreGState(ctx);

let image = UIGraphicsGetImageFromCurrentImageContext()

UIGraphicsEndImageContext()

Answer 2

这都是简单的几何形状。

使用drawRect:代码中的上下文转换矩阵，您应该使用：

CGPoint lastPoint = CGPointMake(radius * cos(endAngle), radius * sin(endAngle));

重置后或安装CTM之前，您应该使用：

//Replace "what should i do here" comment with following code:
CGPoint lastPoint = CGPointZero;
lastPoint.x = center.x + radius * cos(endAngle - M_PI * 0.5);
lastPoint.y = center.y + radius * sin(endAngle - M_PI * 0.5);

此外，第二个解决方案将在drawRect: implementation之外工作。