在一组给定点之间绘制贝塞尔曲线

Question

在iOS应用程序中绘制贝塞尔曲线的最佳方法是什么,它通过一组给定的点

Answer 1

例如,通过查看BEMSimpleLineGraph GitHub项目可以实现更通用的方法(请参阅此处了解更多信息:bemsimplelinegraph).在这里,我提取了一种方法,通过给定的点列表绘制贝塞尔曲线.

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

实施(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

您可以通过使用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并将其添加到UIView.

希望这可以帮助.

Answer 2

您可以轻松地在网上搜索一些有关如何创建贝塞尔曲线的示例。我找到了这个短促的例子。

您可以使用以下代码片段创建闭合贝塞尔曲线：

UIBezierPath* path = [UIBezierPath bezierPath];

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

[path closePath];

我希望它能作为一个起点有所帮助。