UIBezierPath繪製視圖的模糊屏幕截圖

Question

我使用UIBezierPath方法和coretext繪製我的圖形視圖。我使用addQuadCurveToPoint:controlPoint:方法在圖上繪製曲線。我還使用CATiledLayer用於在x軸上繪製大數據集的圖形。我在圖像上下文中繪製了我的整個圖形，並在我的視圖的drawrect:方法中繪製了我的整個視圖中的這個圖像。以下是我的代碼。

- (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]; 
} 

但是在屏幕截圖中，兩點之間繪製的曲線並不平滑。我還在我的信息列表中將「抗鋸齒渲染」設置爲「是」。請看截圖。

Answer 1

我們不得不看你如何構建UIBezierPath，但以我的經驗，爲流暢的曲線，關鍵的問題是，是否該線的曲線的控制點和特定區段的結束點之間的斜率的曲線等於曲線起點下一段與其控制點之間的斜率。我發現使用addCurveToPoint而不是addQuadCurveToPoint可以更容易地繪製一般smogooth曲線，以便我可以更一般地調整起始和結束控制點以滿足此準則。

爲了說明這一點，我通常繪製UIBezierPath曲線的方式是在曲線上有一個點陣列，曲線在該點應該採取的角度，然後控制點的「權重」 （即控制點應該有多遠）。因此，我使用這些參數來指定UIBezierPath的第二個控制點和UIBezierPath的下一個段的第一個控制點。因此，舉例來說：

@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 

然後，我如何使用這樣的例子：

- (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; 
} 

---

當我渲染成UIImage（使用下面的代碼）這個，我不沒有看到圖像的任何軟化，但可以肯定的是圖像不完全相同。 （我比較capture所呈現的圖像與通過同時按下我的物理設備上的電源和主頁按鈕以手動方式捕獲的圖像）。

如果您看到一些軟化，我會建議renderInContext（如下所示）。我想知道你是否把圖像寫成JPG（這是有損的）。也許嘗試PNG，如果你使用JPG。

- (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]; 
}