我需要在Draw应用程序的末尾用箭头绘制线条。我不擅长三角学，所以无法解决这个问题。
用户将手指放在屏幕上并沿任何方向画线。因此，箭头应出现在行尾。
I've posted a Swift version of this answer separately.
这是一个有趣的小问题。首先，有很多方法可以绘制箭头，弯曲或直边。让我们选择一种非常简单的方法并标记我们需要的测量值：
我们想要编写一个函数来获取起点，终点，尾部宽度，头部宽度和头部长度，并返回一个概述箭头形状的路径。让我们创建一个名为dqd_arrowhead的类别，将此方法添加到UIBezierPath：
// UIBezierPath+dqd_arrowhead.h
@interface UIBezierPath (dqd_arrowhead)
+ (UIBezierPath *)dqd_bezierPathWithArrowFromPoint:(CGPoint)startPoint
toPoint:(CGPoint)endPoint
tailWidth:(CGFloat)tailWidth
headWidth:(CGFloat)headWidth
headLength:(CGFloat)headLength;
@end
由于箭头路径上有七个角，让我们通过命名常量来开始实现：
// UIBezierPath+dqd_arrowhead.m
#import "UIBezierPath+dqd_arrowhead.h"
#define kArrowPointCount 7
@implementation UIBezierPath (dqd_arrowhead)
+ (UIBezierPath *)dqd_bezierPathWithArrowFromPoint:(CGPoint)startPoint
toPoint:(CGPoint)endPoint
tailWidth:(CGFloat)tailWidth
headWidth:(CGFloat)headWidth
headLength:(CGFloat)headLength {
好的，简单的部分就完成了。现在，我们如何在路径上找到这七个点的坐标？如果箭头沿X轴对齐，则更容易找到点：
在轴对齐的箭头上计算点坐标非常容易，但是我们需要箭头的总长度才能完成。我们将使用标准库中的hypotf函数：
CGFloat length = hypotf(endPoint.x - startPoint.x, endPoint.y - startPoint.y);
我们将调用辅助方法来实际计算七个点：
CGPoint points[kArrowPointCount];
[self dqd_getAxisAlignedArrowPoints:points
forLength:length
tailWidth:tailWidth
headWidth:headWidth
headLength:headLength];
但我们需要转换这些点，因为通常我们不会尝试创建轴对齐的箭头。幸运的是，Core Graphics支持一种称为仿射变换的变换，它允许我们旋转和平移（滑动）点。我们将调用另一个辅助方法来创建转换，将我们的轴对齐箭头转换为我们要求的箭头：
CGAffineTransform transform = [self dqd_transformForStartPoint:startPoint
endPoint:endPoint
length:length];
现在我们可以使用轴对齐箭头的点和将其转换为我们想要的箭头的转换来创建核心图形路径：
CGMutablePathRef cgPath = CGPathCreateMutable();
CGPathAddLines(cgPath, &transform, points, sizeof points / sizeof *points);
CGPathCloseSubpath(cgPath);
最后，我们可以在UIBezierPath周围包裹一个CGPath并将其返回：
UIBezierPath *uiPath = [UIBezierPath bezierPathWithCGPath:cgPath];
CGPathRelease(cgPath);
return uiPath;
}
这是计算点坐标的辅助方法。这很简单。如果需要，请参阅轴对齐箭头图。
+ (void)dqd_getAxisAlignedArrowPoints:(CGPoint[kArrowPointCount])points
forLength:(CGFloat)length
tailWidth:(CGFloat)tailWidth
headWidth:(CGFloat)headWidth
headLength:(CGFloat)headLength {
CGFloat tailLength = length - headLength;
points[0] = CGPointMake(0, tailWidth / 2);
points[1] = CGPointMake(tailLength, tailWidth / 2);
points[2] = CGPointMake(tailLength, headWidth / 2);
points[3] = CGPointMake(length, 0);
points[4] = CGPointMake(tailLength, -headWidth / 2);
points[5] = CGPointMake(tailLength, -tailWidth / 2);
points[6] = CGPointMake(0, -tailWidth / 2);
}
计算仿射变换更复杂。这是三角学的用武之地。你可以使用atan2和CGAffineTransformRotate和CGAffineTransformTranslate函数来创建它，但如果你记得足够的三角函数，你可以直接创建它。有关我在这里做什么的更多信息，请咨询“The Math Behind the Matrices” in the Quartz 2D Programming Guide：
+ (CGAffineTransform)dqd_transformForStartPoint:(CGPoint)startPoint
endPoint:(CGPoint)endPoint
length:(CGFloat)length {
CGFloat cosine = (endPoint.x - startPoint.x) / length;
CGFloat sine = (endPoint.y - startPoint.y) / length;
return (CGAffineTransform){ cosine, sine, -sine, cosine, startPoint.x, startPoint.y };
}
@end
我已将所有代码放在a gist for easy copy'n'paste中。
使用此类别，您可以轻松绘制箭头：
由于您只是生成一个路径，您可以选择不填充它，或者不要像在此示例中那样对其进行描边：
但是你必须要小心。如果您将头部宽度小于尾部宽度，或者使头部长度大于总箭头长度，则此代码不会阻止您获得时髦的结果：
这是我旧的Objective-C代码的Swift版本。它应该适用于Swift 3.2及更高版本。
extension UIBezierPath {
static func arrow(from start: CGPoint, to end: CGPoint, tailWidth: CGFloat, headWidth: CGFloat, headLength: CGFloat) -> UIBezierPath {
let length = hypot(end.x - start.x, end.y - start.y)
let tailLength = length - headLength
func p(_ x: CGFloat, _ y: CGFloat) -> CGPoint { return CGPoint(x: x, y: y) }
let points: [CGPoint] = [
p(0, tailWidth / 2),
p(tailLength, tailWidth / 2),
p(tailLength, headWidth / 2),
p(length, 0),
p(tailLength, -headWidth / 2),
p(tailLength, -tailWidth / 2),
p(0, -tailWidth / 2)
]
let cosine = (end.x - start.x) / length
let sine = (end.y - start.y) / length
let transform = CGAffineTransform(a: cosine, b: sine, c: -sine, d: cosine, tx: start.x, ty: start.y)
let path = CGMutablePath()
path.addLines(between: points, transform: transform)
path.closeSubpath()
return self.init(cgPath: path)
}
}
以下是您如何调用它的示例：
let arrow = UIBezierPath.arrow(from: CGPoint(x: 50, y: 100), to: CGPoint(x: 200, y: 50),
tailWidth: 10, headWidth: 25, headLength: 40)
//This is the integration into the view of the previous exemple
//Attach the following class to your view in the xib file
#import <UIKit/UIKit.h>
@interface Arrow : UIView
@end
#import "Arrow.h"
#import "UIBezierPath+dqd_arrowhead.h"
@implementation Arrow
{
CGPoint startPoint;
CGPoint endPoint;
CGFloat tailWidth;
CGFloat headWidth;
CGFloat headLength;
UIBezierPath *path;
}
- (id)initWithCoder:(NSCoder *)aDecoder
{
if (self = [super initWithCoder:aDecoder])
{
[self setMultipleTouchEnabled:NO];
[self setBackgroundColor:[UIColor whiteColor]];
}
return self;
}
- (void)drawRect:(CGRect)rect {
[[UIColor redColor] setStroke];
tailWidth = 4;
headWidth = 8;
headLength = 8;
path = [UIBezierPath dqd_bezierPathWithArrowFromPoint:(CGPoint)startPoint
toPoint:(CGPoint)endPoint
tailWidth:(CGFloat)tailWidth
headWidth:(CGFloat)headWidth
headLength:(CGFloat)headLength];
[path setLineWidth:2.0];
[path stroke];
}
- (void) touchesBegan:(NSSet*)touches withEvent:(UIEvent*)event
{
UITouch* touchPoint = [touches anyObject];
startPoint = [touchPoint locationInView:self];
endPoint = [touchPoint locationInView:self];
[self setNeedsDisplay];
}
-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch* touch = [touches anyObject];
endPoint=[touch locationInView:self];
[self setNeedsDisplay];
}
-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch* touch = [touches anyObject];
endPoint = [touch locationInView:self];
[self setNeedsDisplay];
}
@end
在Swift 3.0中，您可以实现这一目标
extension UIBezierPath {
class func arrow(from start: CGPoint, to end: CGPoint, tailWidth: CGFloat, headWidth: CGFloat, headLength: CGFloat) -> Self {
let length = hypot(end.x - start.x, end.y - start.y)
let tailLength = length - headLength
func p(_ x: CGFloat, _ y: CGFloat) -> CGPoint { return CGPoint(x: x, y: y) }
var points: [CGPoint] = [
p(0, tailWidth / 2),
p(tailLength, tailWidth / 2),
p(tailLength, headWidth / 2),
p(length, 0),
p(tailLength, -headWidth / 2),
p(tailLength, -tailWidth / 2),
p(0, -tailWidth / 2)
]
let cosine = (end.x - start.x) / length
let sine = (end.y - start.y) / length
var transform = CGAffineTransform(a: cosine, b: sine, c: -sine, d: cosine, tx: start.x, ty: start.y)
let path = CGMutablePath()
path.addLines(between: points, transform: transform)
path.closeSubpath()
return self.init(cgPath: path)
}
}