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我正在使用UIBezierPath方法和核心文本绘制我的图形视图。我使用 addQuadCurveToPoint:controlPoint:方法在图形上绘制曲线。我还CATiledLayer用于在 x 轴上使用大型数据集渲染图形。我在图像上下文中绘制我的整个图表，并在drawrect:我的视图中我在我的整个视图中绘制这个图像。以下是我的代码。

- (void)drawImage{

        UIGraphicsBeginImageContextWithOptions(self.frame.size, NO, 0.0);

        // Draw Curves 
        [self drawDiagonal];

        UIImage *screenshot = UIGraphicsGetImageFromCurrentImageContext();
        [screenshot retain];
        UIGraphicsEndImageContext();
}
- (void)drawRect:(CGRect)rect{

    NSLog(@"Draw iN rect with Bounds: %@",NSStringFromCGRect(rect));
    [screenshot drawInRect:self.frame];
}

然而，在屏幕截图中，两点之间绘制的曲线并不平滑。我还在我的信息列表中将带有抗锯齿的渲染设置为“是”。请看截图。 在此处输入图像描述

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1 回答 1

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我们必须看看你是如何构造 的UIBezierPath，但根据我的经验，对于平滑曲线，关键问题是曲线的控制点和曲线特定段的端点之间的直线斜率是否等于曲线起点的下一段与其控制点之间的斜率。我发现使用addCurveToPoint而不是更容易绘制一般平滑曲线addQuadCurveToPoint，因此我可以调整起点和终点控制点以更普遍地满足此标准。

为了说明这一点，我通常绘制UIBezierPath曲线的方式是在曲线上有一个点数组，以及曲线在该点应该采取的角度，然后是addCurveToPoint控制点的“权重”（即距离控制点应该是）。因此，我使用这些参数来指示 a 的第二个控制点UIBezierPath和UIBezierPath. 因此，例如：

@interface BezierPoint : NSObject
@property CGPoint point;
@property CGFloat angle;
@property CGFloat weight;
@end

@implementation BezierPoint

- (id)initWithPoint:(CGPoint)point angle:(CGFloat)angle weight:(CGFloat)weight
{
    self = [super init];

    if (self)
    {
        self.point  = point;
        self.angle  = angle;
        self.weight = weight;
    }

    return self;
}

@end

然后，我如何使用它的一个例子：

- (void)loadBezierPointsArray
{
    // clearly, you'd do whatever is appropriate for your chart.
    // this is just a unclosed loop. But it illustrates the idea.

    CGPoint startPoint = CGPointMake(self.view.frame.size.width / 2.0, 50);

    _bezierPoints = [NSMutableArray arrayWithObjects:
            [[BezierPoint alloc] initWithPoint:CGPointMake(startPoint.x, startPoint.y) 
                                         angle:M_PI_2 * 0.05
                                        weight:100.0 / 1.7],
            [[BezierPoint alloc] initWithPoint:CGPointMake(startPoint.x + 100.0, startPoint.y + 70.0) 
                                         angle:M_PI_2
                                        weight:70.0 / 1.7],
            [[BezierPoint alloc] initWithPoint:CGPointMake(startPoint.x, startPoint.y + 140.0)
                                         angle:M_PI
                                        weight:100.0 / 1.7],
            [[BezierPoint alloc] initWithPoint:CGPointMake(startPoint.x - 100.0, startPoint.y + 70.0)
                                         angle:M_PI_2 * 3.0
                                        weight:70.0 / 1.7],
            [[BezierPoint alloc] initWithPoint:CGPointMake(startPoint.x + 10.0, startPoint.y + 10)
                                         angle:0.0
                                        weight:100.0 / 1.7],
            nil];
}

- (CGPoint)calculateForwardControlPoint:(NSUInteger)index
{
    BezierPoint *bezierPoint = _bezierPoints[index];

    return CGPointMake(bezierPoint.point.x + cosf(bezierPoint.angle) * bezierPoint.weight,  
                       bezierPoint.point.y + sinf(bezierPoint.angle) * bezierPoint.weight);
}

- (CGPoint)calculateReverseControlPoint:(NSUInteger)index
{
    BezierPoint *bezierPoint = _bezierPoints[index];

    return CGPointMake(bezierPoint.point.x - cosf(bezierPoint.angle) * bezierPoint.weight,  
                       bezierPoint.point.y - sinf(bezierPoint.angle) * bezierPoint.weight);
}

- (UIBezierPath *)bezierPath
{
    UIBezierPath *path = [UIBezierPath bezierPath];
    BezierPoint *bezierPoint = _bezierPoints[0];

    [path moveToPoint:bezierPoint.point];

    for (NSInteger i = 1; i < [_bezierPoints count]; i++)
    {
        bezierPoint = _bezierPoints[i];

        [path addCurveToPoint:bezierPoint.point
                controlPoint1:[self calculateForwardControlPoint:i - 1] 
                controlPoint2:[self calculateReverseControlPoint:i]];
    }

    return path;
}

当我将其渲染为UIImage（使用下面的代码）时，我看不到图像有任何软化，但不可否认，图像并不相同。（我正在将capture通过同时按下物理设备上的电源和主页按钮手动捕获的图像与我手动捕获的图像进行比较。）

如果您看到一些软化，我会建议renderInContext（如下所示）。我想知道您是否将图像写为 JPG（有损）。如果您使用 JPG，也许可以尝试 PNG。

- (void)drawBezier
{
    UIBezierPath *path = [self bezierPath];

    CAShapeLayer *oval = [[CAShapeLayer alloc] init];
    oval.path = path.CGPath;
    oval.strokeColor = [UIColor redColor].CGColor;
    oval.fillColor = [UIColor clearColor].CGColor;
    oval.lineWidth = 5.0;
    oval.strokeStart = 0.0;
    oval.strokeEnd = 1.0;
    [self.view.layer addSublayer:oval];
}

- (void)capture
{
    UIGraphicsBeginImageContextWithOptions(self.view.frame.size, NO, 0.0);
    CGContextRef context = UIGraphicsGetCurrentContext();
    [self.view.layer renderInContext:context];
    UIImage *screenshot = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    // save the image

    NSData *data = UIImagePNGRepresentation(screenshot);
    NSString *documentsPath = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)[0];
    NSString *imagePath = [documentsPath stringByAppendingPathComponent:@"image.png"];
    [data writeToFile:imagePath atomically:YES];

    // send it to myself so I can look at the file

    NSURL *url = [NSURL fileURLWithPath:imagePath];
    UIActivityViewController *controller = [[UIActivityViewController alloc] initWithActivityItems:@[url]
                                                                         applicationActivities:nil];
    [self presentViewController:controller animated:YES completion:nil];
}
于 2012-12-24T13:35:14.927 回答