Drawing gradient over image in ios - ios

Question

How to create gradient colour look like following image programatically.

Answer 1

When you say "apply it over the image as a gradient", do you mean as a mask (revealing the image at the top, having it fade the image to transparent at the bottom)? If that's the case, you can apply that gradient as a mask, using CAGradientLayer:
CAGradientLayer *gradientMask = [CAGradientLayer layer];
gradientMask.frame = self.imageView.bounds;
gradientMask.colors = #[(id)[UIColor whiteColor].CGColor,
(id)[UIColor clearColor].CGColor];
self.imageView.layer.mask = gradientMask;
The above does a simple vertical gradient (because the default is vertical, linear gradient). But you asked about startPoint, endPoint, and locations. If for example, you wanted your mask applied horizontally, you would do:
gradientMask.startPoint = CGPointMake(0.0, 0.5); // start at left middle
gradientMask.endPoint = CGPointMake(1.0, 0.5); // end at right middle
If you wanted to have two gradients, one at the first 10% and another at the last 10%, you'd do:
gradientMask.colors = #[(id)[UIColor clearColor].CGColor,
(id)[UIColor whiteColor].CGColor,
(id)[UIColor whiteColor].CGColor,
(id)[UIColor clearColor].CGColor];
gradientMask.locations = #[#0.0, #0.10, #0.90, #1.0];
If you want a simple gradient by itself (not as a mask), you'd create a view and then add the gradient layer to it:
CAGradientLayer *gradient = [CAGradientLayer layer];
gradient.frame = view.bounds;
gradient.colors = #[(id)[UIColor whiteColor].CGColor,
(id)[UIColor blackColor].CGColor];
[view.layer addSublayer:gradient];
See the CAGradientLayer class reference.

Answer 2

I just wrote an UIImage extension for Swift 2.0. Maybe it's of some use. You call it with an array of UIColor (any number) and a frame where the gradient should be drawn.
extension UIImage {
class func convertGradientToImage(colors: [UIColor], frame: CGRect) -> UIImage {
// start with a CAGradientLayer
let gradientLayer = CAGradientLayer()
gradientLayer.frame = frame
// add colors as CGCologRef to a new array and calculate the distances
var colorsRef = [CGColor]()
var locations = [NSNumber]()
for i in 0 ... colors.count-1 {
colorsRef.append(colors[i].CGColor as CGColorRef)
locations.append(Float(i)/Float(colors.count-1))
}
gradientLayer.colors = colorsRef
gradientLayer.locations = locations
// now build a UIImage from the gradient
UIGraphicsBeginImageContext(gradientLayer.bounds.size)
gradientLayer.renderInContext(UIGraphicsGetCurrentContext()!)
let gradientImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
// return the gradient image
return gradientImage
}
}
Call it like this:
let colors = [
UIColor.blueColor(),
UIColor.greenColor()
// and many more if you wish
]
let gradientImage = UIImage.convertGradientToImage(colors, frame: navigationBar.bounds)
and apply with:
.backgroundColor = UIColor(patternImage: gradientImage)
or
.setBackgroundImage(gradientImage, forBarMetrics: .Default)

Answer 3

CAGradientLayer *gradient = [CAGradientLayer layer];
gradient.frame = self.view.bounds;
gradient.startPoint = CGPointMake(1.0, 1.0); //Dark From bottom
gradient.endPoint = CGPointMake(1.0, 0);
gradient.colors = [NSArray arrayWithObjects:
(id)[[UIColor blackColor] CGColor],
(id)[[UIColor clearColor] CGColor], nil];
[self.view.layer insertSublayer:gradient atIndex:0];

Answer 4

This is the best approach, working for me as requirement
CAGradientLayer *gradientLayer = [CAGradientLayer layer];
gradientLayer.frame = yourImageView.layer.bounds;
gradientLayer.colors = [NSArray arrayWithObjects:
(id)[UIColor colorWithWhite:1.0f alpha:1.0f].CGColor,
(id)[UIColor colorWithWhite:0.0f alpha:0.9f].CGColor,
nil];
gradientLayer.locations = [NSArray arrayWithObjects:
[NSNumber numberWithFloat:0.0f],
[NSNumber numberWithFloat:1.0f],
nil];
[yourImageView.layer addSublayer:gradientLayer];

Answer 5

-(void) drawGradientinBounds: (CGRect) currentBounds withColors:(NSArray*) colors andPercentages:(NSArray *)percentages andGradientDirectionIsVertical:(BOOL)isGradientDirectionVertical
{
CGContextRef currentContext = UIGraphicsGetCurrentContext();
CGGradientRef glossGradient;
CGColorSpaceRef rgbColorspace;
size_t num_locations = [percentages count];
CGFloat locations[num_locations];
for(int i=0;i<num_locations;i++)
locations[i] = [[percentages objectAtIndex:i] floatValue];
int comps = [colors count]*4;
CGFloat components[comps];
for(int i = [colors count]-1;i>=0;i--)
{
comps--;
UIColor *c = [colors objectAtIndex:i];
const CGFloat *cg = CGColorGetComponents([c CGColor]);
components[comps] = cg[3];
comps--;
components[comps] = cg[2];
comps--;
components[comps] = cg[1];
comps--;
components[comps] = cg[0];
}
rgbColorspace = CGColorSpaceCreateDeviceRGB();
glossGradient = CGGradientCreateWithColorComponents(rgbColorspace, components, locations, num_locations);
CGPoint topCenter;
CGPoint endCenter;
if(isGradientDirectionVertical)
{
topCenter = CGPointMake(CGRectGetMidX(currentBounds), currentBounds.origin.y);
endCenter = CGPointMake(CGRectGetMidX(currentBounds), CGRectGetHeight(currentBounds)+currentBounds.origin.y);
}
else
{
topCenter = CGPointMake( currentBounds.origin.x,CGRectGetMidY(currentBounds));
endCenter = CGPointMake(CGRectGetWidth(currentBounds)+currentBounds.origin.x,CGRectGetMidY(currentBounds));
}
CGContextDrawLinearGradient(currentContext, glossGradient, topCenter, endCenter, 0);
CGGradientRelease(glossGradient);
CGColorSpaceRelease(rgbColorspace);
}
And the input to this method are bounds, colorArray:
[NSArray arrayWithObjects:[UIColor blackColor], [UIColor whiteColor], nil]
percentageArray:
[NSArray arrayWithObjects:[NSNumber numberWithFloat:0.0], [NSNumber numberWithFloat:1.0], nil]