在一组给定的点之间绘制贝塞尔曲线

Question

在iOS应用程序中，通过一组给定点绘制贝塞尔曲线的最佳方式是什么。

- user462455

Answer 1

一种更加通用的方法是通过查看BEMSimpleLineGraph GitHub项目（有关更多信息，请参见bemsimplelinegraph）来实现。这里我提取了一种绘制给定点列表中的贝塞尔曲线的方法。

头文件（BezierLine.h）：

#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>
#import <CoreGraphics/CoreGraphics.h>

@interface BezierLine : NSObject

/*
 Draws a bezier curved line on the given context
 with points: Array of CGPoint values
 */
-(void) drawBezierCurveInContext:(CGContextRef)context withPoints:(NSArray*)points lineColor:(UIColor*)color lineWidth:(CGFloat)lineWidth;

@end

实现（BezierLine.m）：

#import "BezierLine.h"

@implementation BezierLine

-(void) drawBezierCurveInContext:(CGContextRef)context withPoints:(NSArray*)points lineColor:(UIColor*)color lineWidth:(CGFloat)lineWidth {
    if (points.count < 2) return;

    CGPoint CP1;
    CGPoint CP2;

    // LINE
    UIBezierPath *line = [UIBezierPath bezierPath];

    CGPoint p0;
    CGPoint p1;
    CGPoint p2;
    CGPoint p3;
    CGFloat tensionBezier1 = 0.3;
    CGFloat tensionBezier2 = 0.3;

    CGPoint previousPoint1;
    CGPoint previousPoint2;

    [line moveToPoint:[[points objectAtIndex:0] CGPointValue]];

    for (int i = 0; i < points.count - 1; i++) {
        p1 = [[points objectAtIndex:i] CGPointValue];
        p2 = [[points objectAtIndex:i + 1] CGPointValue];

        const CGFloat maxTension = 1.0f / 3.0f;
        tensionBezier1 = maxTension;
        tensionBezier2 = maxTension;

        if (i > 0) { // Exception for first line because there is no previous point
            p0 = previousPoint1;
            if (p2.y - p1.y == p1.y - p0.y) tensionBezier1 = 0;
        } else {
            tensionBezier1 = 0;
            p0 = p1;
        }

        if (i < points.count - 2) { // Exception for last line because there is no next point
            p3 = [[points objectAtIndex:i + 2] CGPointValue];
            if (p3.y - p2.y == p2.y - p1.y) tensionBezier2 = 0;
        } else {
            p3 = p2;
            tensionBezier2 = 0;
        }

        // The tension should never exceed 0.3
        if (tensionBezier1 > maxTension) tensionBezier1 = maxTension;
        if (tensionBezier2 > maxTension) tensionBezier2 = maxTension;

        // First control point
        CP1 = CGPointMake(p1.x + (p2.x - p1.x)/3,
                          p1.y - (p1.y - p2.y)/3 - (p0.y - p1.y)*tensionBezier1);

        // Second control point
        CP2 = CGPointMake(p1.x + 2*(p2.x - p1.x)/3,
                          (p1.y - 2*(p1.y - p2.y)/3) + (p2.y - p3.y)*tensionBezier2);


        [line addCurveToPoint:p2 controlPoint1:CP1 controlPoint2:CP2];

        previousPoint1 = p1;
        previousPoint2 = p2;
    }

    CGContextSetAllowsAntialiasing(context, YES);
    CGContextSetStrokeColorWithColor(context, color.CGColor);
    CGContextSetLineWidth(context, lineWidth);
    CGContextAddPath(context, line.CGPath);
    CGContextDrawPath(context, kCGPathStroke);
}


@end

你可以通过使用 UIGraphicsBeginImageContext 创建图像上下文并使用 UIGraphicsGetCurrentContext() 检索上下文来使用它。

否则，您可能希望更改代码并将结果路径分配给 CALayer，然后将其添加到 UIView 中。

希望这可以帮助到您。

- mjrehder

Answer 2

我知道可能已经晚了，但是为了那些正在寻找正确答案的人。你可以使用 addCurveToPoint 来绘制曲线，而不是使用 addLineToPoint 来绘制直线。例如：

[bezierPath moveToPoint:CGPointMake(0, 0)];
[bezierPath addCurveToPoint:CGPointMake(40, 100) 
              controlPoint1:CGPointMake(20, 0) 
              controlPoint2:CGPointMake(20, 100)];
[bezierPath addCurveToPoint:CGPointMake(80, 50) 
              controlPoint1:CGPointMake(60, 100) 
              controlPoint2:CGPointMake(60, 50)];

// and you may don't want to close the path
// [bezierPath closePath];

选择曲线的控制点由您决定。我仅使用 x=last_point_x + 20; y=last_point_y 作为控制点一，以及 x=current_point_x - 20; y=current_point_y;

您可能需要使用其他值，而不是20，因为曲线的不同段宽度可能会产生影响。

- codingrhythm

Answer 3

请尝试这个。

UIImageView *waterLevel = [[UIImageView alloc] initWithFrame:CGRectMake(0,0,200,200)];
UIGraphicsBeginImageContext(waterLevel.frame.size);
[waterLevel.image drawAtPoint:CGPointZero];
//define BezierPath
UIBezierPath *bezierPath = [UIBezierPath bezierPath];


// Set the starting point of the shape.
[bezierPath moveToPoint:CGPointMake(0, 0)];

[bezierPath addLineToPoint:CGPointMake(waterLevel.frame.size.width, 0)];
[bezierPath addLineToPoint:CGPointMake(waterLevel.frame.size.width, waterLevel.frame.size.height)];
[bezierPath addLineToPoint:CGPointMake(0, waterLevel.frame.size.height)];
[bezierPath closePath];

bezierPath.lineWidth = 15;
//set the stoke color
[[UIColor blackColor] setStroke];
//draw the path
[bezierPath stroke];

// Add to the current Graphic context
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextAddPath(context,bezierPath.CGPath);
waterLevel.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

[self.view addSubview:waterLevel];

- Milan Kamilya

---

请在对代码进行贬低之前分享您的问题。 - Milan Kamilya

bechara - kheye gechilo :P - Maniac One

Answer 4

你可以在网上轻松搜索到一些创建贝塞尔曲线的例子。我找到了这个简短的教程作为示例。

你可以使用以下代码片段创建一个闭合的贝塞尔曲线：

UIBezierPath* path = [UIBezierPath bezierPath];

[path moveToPoint:pt1];
[path addLineToPoint:pt2];
[path addLineToPoint:pt3];

[path closePath];

I hope it will help as a starting point.

- tiguero

Answer 5

使用CGPointFromString方法可以更加高效：

 NSArray *pointArray = @[@"{3.0,2.5}",@"{100.0,30.2}", @"{100.0,200.0}", @"{3.0,200.0}"];

// draw the path
UIBezierPath *aPath = [UIBezierPath bezierPath];
for (NSString *pointString in pointArray) {
    if ([pointArray indexOfObject:pointString] == 0)
        [aPath moveToPoint:CGPointFromString(pointString)];
    else
        [aPath addLineToPoint:CGPointFromString(pointString)];
}
[aPath closePath];

- fawrkes

Answer 6

UIBezierPath *aPath = [UIBezierPath bezierPath];

// Set the starting point of the shape.
[aPath moveToPoint:CGPointMake(100.0, 0.0)];

// Draw the lines.
[aPath addLineToPoint:CGPointMake(200.0, 40.0)];
[aPath addLineToPoint:CGPointMake(160, 140)];
[aPath addLineToPoint:CGPointMake(40.0, 140)];
[aPath addLineToPoint:CGPointMake(0.0, 40.0)];
[aPath closePath];

- Abdul

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这只是画直线，并没有回答问题。 - FractalDoctor