iOS draw gradient in part of the view - objective-c

Question

I've created a custom progress bar which subclass UIView and implements drawRect. I manage to draw a single gradient on the entire view. I'd like however to draw several different gradients, each one in a different position. How to I limit CGContextDrawLinearGradient to smaller rect inside my view?
glossGradient = CGGradientCreateWithColorComponents(rgbColorspace, components, locations, num_locations);
CGPoint topCenter = CGPointMake(start + (CGRectGetMidX(currentBounds)/currentBounds.size.width), 0.0f);`
CGPoint midCenter = CGPointMake(start + (CGRectGetMidX(currentBounds)/currentBounds.size.width), currentBounds.size.height);
CGContextDrawLinearGradient(currentContext, glossGradient, topCenter, midCenter, 0);
start = start + (values[i] / currentBounds.size.width);
CGGradientRelease(glossGradient);
}

Answer 1

You can use CGContectClipToRect to restrict the drawing area
Then for each gradient do:
CGContextSaveGState(currentContext);
CGContextClipToRect(theRect); // theRect should be the area where you want to draw the gradient
... // gradient drawing code
CGContextRestoreGState(currentContext);

Answer 2

As stated in Quartz 2D Programming Guide:
When you paint a gradient, Quartz fills the current context. Painting
a gradient is different from working with colors and patterns, which
are used to stroke and fill path objects. As a result, if you want
your gradient to appear in a particular shape, you need to clip the
context accordingly.
Since you want to draw each gradient in a rectangle, you will want to do something like this for each gradient and rectangle:
CGContextSaveGState(currentContext); {
CGContextClipToRect(currentContext, currentBounds);
CGContextDrawLinearGradient(currentContext, glossGradient, topCenter, midCenter, 0);
} CGContextRestoreGState(currentContext);