iOS：获取 CGMutablePath 不在 drawRect 中：并将其分配给 CAShapeLayer 的路径

Posted 2023-02-25

【中文标题】iOS：获取 CGMutablePath 不在 drawRect 中：并将其分配给 CAShapeLayer 的路径

【英文标题】：iOS: Getting CGMutablePath not in drawRect: and Assign it to CAShapeLayer's Path

【发布时间】：2013-06-15 21:31:04

【问题描述】：

我已经为此苦苦思索了好几个小时。我试着阅读并寻找答案。我什至尝试过“走开，然后再回来”的方法，但没有奏效。我什至尝试过瑜伽和冥想！我没有占上风。。

所以请各位高手赐教。

我只是想获取不在 drawRect 内的 CGPath 的副本：

CGMutablePathRef path = CGPathCreateMutable();
CGPathMoveToPoint(path, ......);
CGPathAddLineToPoint(path, ....);
CGPathAddLineToPoint(path, ....);
CGPathAddLineToPoint(path, ....);
CGPathAddLineToPoint(path, ....);

最后： CGPathCloseSubpath(path); CGContextAddPath(context, path); 那没有用，所以我也尝试使用而不是上面的 2 个调用： CGPathCreateMutableCopy(path); 最终 - 我只是希望能够获取此路径并将其作为路径插入 CAShapeLayer 并通过进行此调用为其设置动画：

animation.toValue = [UIBezierPath bezierPathWithCGPath:path];

因此，在我尝试进行另一项放松活动（例如不带降落伞的跳伞）以理清思路并最终做到这一点之前，您能帮我举几个例子吗？除此之外，您能否详细解释一下使用以下函数的正确方法： CGPathCloseSubpath(path); CGContextAddPath(context, path); CGPathCreateMutableCopy(path);

提前致谢。

【问题讨论】：

我不确定你想在这里做什么。你想要一个返回 CGMutablePath 的方法吗？

@Inafziger：嗨，我只是想创建 CGPath。但是从 Apple 的文档和 *** 上的文字来看，上述函数都不能在 drawRect: 之外调用。而不是依赖于系统调用 setNeedsDisplay: 依次调用 drawRect: 我希望能够在 drawRect: 之外的其他地方获取路径，但是如果我在 drawRect: 之外调用上述内容，我会得到一个 nil 0x0 上下文例外。谢谢。

【参考方案1】：

CGPath 是具有 C 风格 API 的 C 风格数据结构。基本上它是组成路径的点列表。

CGContext 也是一种用于绘制图像的 C 风格数据结构（可能大一点），即将点转换为彩色像素。

我将我的 sn-ps 放入一个函数中，您可以简单地将其复制并粘贴到单个屏幕 xcode 项目中。您会在代码中找到解释为 cmets 的解释，以及用于深入调试和探索 CGPath 对象的两个函数（我从https://github.com/erica/ios-6-Cookbook 获取并添加了一些内容）。

#import "ViewController.h"
#import "OverlayView.h"
#import <QuartzCore/QuartzCore.h>

@implementation ViewController

- (void)viewDidLoad

    [super viewDidLoad];

    // create a graphics context with the C-API of the QuartzCore framework
    // the graphics context is only required for drawing the path
    CGRect compositionBounds = CGRectMake(30, 30, 300, 508);
    UIGraphicsBeginImageContext(compositionBounds.size);
    CGContextRef ctx = UIGraphicsGetCurrentContext();

    // create a mutable path with QuartzCore
    CGMutablePathRef p1 = CGPathCreateMutable();

    // create a CGPath with UIKit classes using Obj-C
    UIBezierPath *bp = [UIBezierPath bezierPath];
    [bp moveToPoint:(CGPoint)180, 120];
    [bp addLineToPoint:(CGPoint)30, 170];
    [bp addLineToPoint:(CGPoint)135, 175];
    [bp addLineToPoint:(CGPoint)105, 115];
    // if you fill the path during drawing it gets closed implicitly
//    [bp closePath];
    // add the CGPath to our mutable path
    CGPathAddPath(p1, nil, bp.CGPath);

    // add a closed triangle as subpath to our mutable path
    CGPathMoveToPoint(p1, nil, 50, 250);
    CGPoint p2[3];
    p2[0] = CGPointMake(10, 20);
    p2[1] = (CGPoint)210, 50;
    p2[2] = (CGPoint)80, 120;
    CGPathAddLines(p1, nil, p2, 3);
    // explicitly close our last added subpath
    CGPathCloseSubpath(p1);

    // draw our mutable path (with all its subpaths) filling its area
    CGContextAddPath(ctx, p1);
    CGContextSetFillColorWithColor(ctx, [[UIColor redColor] CGColor]);
    CGContextFillPath(ctx);

    // draw our mutable path (with all its subpaths) stroking its outline
    CGContextAddPath(ctx, p1);
    CGContextSetRGBStrokeColor(ctx, 0, 0, 0, 1.0);
    CGContextStrokePath(ctx);

    // display our mutable path in an image view on screen
    UIImage *i = UIGraphicsGetImageFromCurrentImageContext();
    UIImageView *iv = [[UIImageView alloc] initWithImage:i];
    [self.view addSubview:iv];
    iv.frame = self.view.frame;

    // release ressources created with the C-API of QuartzCore
    CGPathRelease(p1);
    UIGraphicsEndImageContext();

    // create a mutable copy of a path and don't use it for drawing
    CGMutablePathRef p3 = CGPathCreateMutableCopy(bp.CGPath);
    NSArray *p3points = [self pointsFromCGPath:p3];
    for (NSValue *point in p3points) 
        NSLog(@"path element in p3: %@", NSStringFromCGPoint(point.CGPointValue));
    
    // note that UIBezierPath takes care of its path itself
    CGPathRelease(p3);



// modified from https://github.com/erica/iOS-6-Cookbook

#define VALUE(_INDEX_) [NSValue valueWithCGPoint:points[_INDEX_]]

void getPointsFromBezier(void *info, const CGPathElement *element)

    NSMutableArray *bezierPoints = (__bridge NSMutableArray *)info;

    // Retrieve the path element type and its points
    CGPathElementType type = element->type;
    CGPoint *points = element->points;

    switch (type) 
        case kCGPathElementMoveToPoint:
            NSLog(@"MoveToPoint (%3.2f, %3.2f", points->x, points->y);
            break;
        case kCGPathElementAddLineToPoint:
            NSLog(@"AddLineToPoint (%3.2f, %3.2f)", points->x, points->y);
            break;
        case kCGPathElementAddQuadCurveToPoint:
            NSLog(@"AddQuadCurveToPoint (%3.2f, %3.2f), (%3.2f, %3.2f)", points->x, points->y, points[1].x, points[1].y);
            break;
        case kCGPathElementAddCurveToPoint:
            NSLog(@"AddCurveToPoint (%3.2f, %3.2f), (%3.2f, %3.2f), (%3.2f, %3.2f)", points->x, points->y, points[1].x, points[1].y, points[2].x, points[2].y);
            break;
        case kCGPathElementCloseSubpath:
            NSLog(@"CloseSubpath (%3.2f, %3.2f)", points->x, points->y);
            break;
        default:
            NSLog(@"unknown");
            break;
    

    // Add the points if they're available (per type)
    if (type != kCGPathElementCloseSubpath)
    
        [bezierPoints addObject:VALUE(0)];
        if ((type != kCGPathElementAddLineToPoint) &&
            (type != kCGPathElementMoveToPoint))
            [bezierPoints addObject:VALUE(1)];
    
    if (type == kCGPathElementAddCurveToPoint)
        [bezierPoints addObject:VALUE(2)];


- (NSArray *)pointsFromCGPath:(CGPathRef)path

    NSMutableArray *points = [NSMutableArray array];
    CGPathApply(path, (__bridge void *)points, getPointsFromBezier);
    return points;