如何繪製一個完整的圓形圖像

Question

我很新的核心圖形。我需要畫一個完整的圈子。我該如何解決它？我目前有一個蒙面的圈子。

我提到this example。

//Use the draw rect to draw the Background, the Circle and the Handle 
-(void)drawRect:(CGRect)rect{ 

    [super drawRect:rect]; 

    CGContextRef ctx = UIGraphicsGetCurrentContext(); 

/** Draw the Background **/ 

    //Create the path 
    CGContextAddArc(ctx, self.frame.size.width/2, self.frame.size.height/2, radius, 0, M_PI *2, 0); 

// CGContextFillEllipseInRect(ctx, CGRectMake(self.frame.size.height/2, self.frame.size.width/2, 100, 100)); 
// CGContextSetRGBFillColor(ctx, 0.5, 0.5, 0.5, 1.0); 


    //Set the stroke color to black 
    [[UIColor greenColor]setStroke]; 

    //Define line width and cap 
    CGContextSetLineWidth(ctx, TB_BACKGROUND_WIDTH); 
    CGContextSetLineCap(ctx, kCGLineCapButt); 

    CGContextDrawPath(ctx, kCGPathStroke); 

    UIGraphicsBeginImageContext(CGSizeMake(TB_SLIDER_SIZE,TB_SLIDER_SIZE)); 
    CGContextRef imageCtx = UIGraphicsGetCurrentContext(); 

    CGContextAddArc(imageCtx, self.frame.size.width/2 , self.frame.size.height/2, radius, 0, ToRad(self.self.startAngle), 0); 

    [[UIColor redColor]set]; 

    CGContextSetLineWidth(imageCtx, TB_LINE_WIDTH); 
    CGContextDrawPath(imageCtx, kCGPathStroke); 

    //save the context content into the image mask 
    CGImageRef mask = CGBitmapContextCreateImage(UIGraphicsGetCurrentContext()); 
    UIGraphicsEndImageContext(); 
    CGContextSaveGState(ctx); 
    CGContextClipToMask(ctx, self.bounds, mask); 
    CGImageRelease(mask); 

    //list of components 
    CGFloat components[8] = { 
     0.0, 0.0, 1.0, 1.0,  // Start color - Blue 
     1.0, 1.0, 1.0, 1.0 }; // End color - Violet 

    CGColorSpaceRef baseSpace = CGColorSpaceCreateDeviceRGB(); 
    CGGradientRef gradient = CGGradientCreateWithColorComponents(baseSpace, components, NULL, 2); 
    CGColorSpaceRelease(baseSpace), baseSpace = NULL; 

    //Gradient direction 
    CGPoint startPoint = CGPointMake(CGRectGetMidX(rect), CGRectGetMinY(rect)); 
    CGPoint endPoint = CGPointMake(CGRectGetMidX(rect), CGRectGetMaxY(rect)); 

    //Draw the gradient 
    CGContextDrawLinearGradient(ctx, gradient, startPoint, endPoint, 0); 
    CGGradientRelease(gradient), gradient = NULL; 

    CGContextRestoreGState(ctx); 

/** Draw the handle **/ 
    [self drawTheHandle:ctx]; 

} 

Answer 1

使backgroup寬度和線寬度140和它的工作原理！

#define TB_BACKGROUND_WIDTH 140 //The width of the dark background 
#define TB_LINE_WIDTH 140   //The width of the active area (the gradient) and the width of the handle 

Answer 2

CGContextDrawPath(imageCtx, kCGPathFill);