Defining angle of the gradient using CAGradientLayer

Question

I am trying to draw angular gradient using CaGradientLayer. I know angle can be defined using startPoint and endPoint. I can compute these points for some standard angles like 0, 90, 180, 360 etc. But I want formulate these points for arbitrary angle. I have tried computing it using some trigonometry, but didn't get any success. Can anyone give me any directions on how to compute these points for arbitrary angles?

Answer 1

Here's a method that creates a view that allows 360 degree rotation of its two-colour gradient based upon input from a slider (or anything). The incoming slider value ("x" variable below) is between 0.0 and 1.0.

At 0.0 the gradient is horizontal (with colour A on top, and colour B below), rotating through 360 degrees to value 1.0 (identical to value 0.0 - or a full rotation).

E.g. when x = 0.25, colour A is left and colour B is right. At 0.5, colour A is below and colour B is above, 0.75 colour A is right and colour B is left. It rotates anti-clockwise from right to left.

It takes four arguments: frame, colourA, colourB and the input value (0-1).

-(UIView *)gradientViewWithFrame:(CGRect)frame colourA:(UIColor *)A colourB:(UIColor *)B rotation:(float)x {

//x is between 0 and 1, eg. from a slider, representing 0 - 360 degrees
//colour A starts on top, with colour B below
//rotations move anti-clockwise

//1. create the colour view
UIView * colourView = [UIView new];
colourView.frame = frame;

//2. create the gradient layer
CAGradientLayer *gradient = [CAGradientLayer layer];
gradient.frame = colourView.bounds;
gradient.colors = [NSArray arrayWithObjects:(id)[A CGColor], (id)[B CGColor], nil];
[colourView.layer insertSublayer:gradient atIndex:0];

//3. create coordinates
float a = pow(sinf((2*M_PI*((x+0.75)/2))),2);
float b = pow(sinf((2*M_PI*((x+0.0)/2))),2);
float c = pow(sinf((2*M_PI*((x+0.25)/2))),2);
float d = pow(sinf((2*M_PI*((x+0.5)/2))),2);

//4. set the gradient direction
[gradient setStartPoint:CGPointMake(a, b)];
[gradient setEndPoint:CGPointMake(c, d)];

return colourView;
}

Answer 2

Swift 3

static func setGradient(view: UIView!,viewRadius: CGFloat!, color1: UIColor!, color2: UIColor!, angle: Double!, alphaValue: CGFloat!){
    let gradient = CAGradientLayer()
    
    gradient.frame =  CGRect(origin: CGPoint.zero, size: view.frame.size)
    
    gradient.colors = [color1.withAlphaComponent(alphaValue).cgColor, color2.withAlphaComponent(alphaValue).cgColor]
    let x: Double! = angle / 360.0
    let a = pow(sinf(Float(2.0 * M_PI * ((x + 0.75) / 2.0))),2.0);
    let b = pow(sinf(Float(2*M_PI*((x+0.0)/2))),2);
    let c = pow(sinf(Float(2*M_PI*((x+0.25)/2))),2);
    let d = pow(sinf(Float(2*M_PI*((x+0.5)/2))),2);
    
    gradient.endPoint = CGPoint(x: CGFloat(c),y: CGFloat(d))
    gradient.startPoint = CGPoint(x: CGFloat(a),y:CGFloat(b))
    
    view.roundCorners([.topLeft, .bottomLeft], radius: viewRadius)
    view.layer.insertSublayer(gradient, at: 0)
    
    
}

Answer 3

This is heavily based on Sarthak Sharma's solution. I made an extension of UIView and I figured the readability and type conversions could be improved a bit:

extension UIView {

    func setGradient(colors: [CGColor], angle: Float = 0) {
        let gradientLayerView: UIView = UIView(frame: CGRect(x:0, y: 0, width: bounds.width, height: bounds.height))
        let gradient: CAGradientLayer = CAGradientLayer()
        gradient.frame = gradientLayerView.bounds
        gradient.colors = colors

        let alpha: Float = angle / 360
        let startPointX = powf(
            sinf(2 * Float.pi * ((alpha + 0.75) / 2)),
            2
        )
        let startPointY = powf(
            sinf(2 * Float.pi * ((alpha + 0) / 2)),
            2
        )
        let endPointX = powf(
            sinf(2 * Float.pi * ((alpha + 0.25) / 2)),
            2
        )
        let endPointY = powf(
            sinf(2 * Float.pi * ((alpha + 0.5) / 2)),
            2
        )

        gradient.endPoint = CGPoint(x: CGFloat(endPointX),y: CGFloat(endPointY))
        gradient.startPoint = CGPoint(x: CGFloat(startPointX), y: CGFloat(startPointY))

        gradientLayerView.layer.insertSublayer(gradient, at: 0)
        layer.insertSublayer(gradientLayerView.layer, at: 0)
    }

}

Add this to a new or a related Swift file and all you have to do is call either myView.setGradient(colors: gradientColorsArray) or myView.setGradient(colors: gradientColorsArray, angle: 90).