Quartz2D和梯度线

Question

我怎样才能用quartz2d绘制渐变线？

Answer 1

CGContextDrawLinearGradient绘制渐变。使用CGContextClipToRect（或相关的裁剪功能）可以裁剪到要用渐变填充的区域。

不支持使用渐变抚摸或填充路径，而是剪切到要填充的区域。

Answer 2

我用这里面drawRect:和工作就像一个魅力：

double slope, cosy, siny; 
double halfWidth = 2; // the thickness of the line will be 2*halfWith 

// the start and end points have to be inside UIView frame coordinates 
CGPoint start = CGPointMake(30, 20); 
CGPoint end = CGPointMake(80, 90); 

slope = atan2((start.y - end.y), (start.x - end.x)); 
cosy = cos(slope); 
siny = sin(slope); 

CGContextRef context = UIGraphicsGetCurrentContext(); 

CGGradientRef myGradient; 
CGColorSpaceRef myColorspace; 
size_t num_locations = 2; 
CGFloat locations[2] = { 0.0, 1.0 }; 
CGFloat components[8] = { 1.0, 1.0, 1.0, 1.0, // Start color (White) 
          1.0, 0.0, 0.0, 1.0 }; // End color (Red) 

myColorspace = CGColorSpaceCreateDeviceRGB(); 
myGradient = CGGradientCreateWithColorComponents (myColorspace, components, locations, num_locations); 

CGContextMoveToPoint(context, start.x -halfWidth*siny , start.y +halfWidth*cosy); 
CGContextAddLineToPoint(context, end.x -halfWidth*siny , end.y +halfWidth*cosy ); 
CGContextAddLineToPoint(context, end.x +halfWidth*siny , end.y -halfWidth*cosy); 
CGContextAddLineToPoint(context, start.x +halfWidth*siny, start.y -halfWidth*cosy); 
CGContextAddLineToPoint(context, start.x -halfWidth*siny , start.y +halfWidth*cosy);  
CGContextClip(context); 

CGContextDrawLinearGradient (context, myGradient, start, end, 0); 
CGColorSpaceRelease(myColorspace); 
CGGradientRelease (myGradient);