iOS smooth gradient using CGShading

SmoothGradientView.m

- (void)drawRect:(CGRect)rect {
	// Draw the gradient background
	CGContextRef context = UIGraphicsGetCurrentContext();
	CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();
 
	// Define the shading callbacks
	CGFunctionCallbacks callbacks = {0, blackShade, NULL};
 
	// As input to our function we want 1 value in the range [0.0, 1.0].
	// This is our position within the 'gradient'.
	size_t domainDimension = 1;
	CGFloat domain[2] = {0.0f, 1.0f};
 
	// The output of our function is 2 values, each in the range [0.0, 1.0].
	// This is our selected color for the input position.
	// The 2 values are the white and alpha components.
	size_t rangeDimension = 2;
	CGFloat range[8] = {0.0f, 1.0f, 0.0f, 1.0f};
 
	// Create the shading finction
	CGFunctionRef function = CGFunctionCreate(NULL, domainDimension, domain, rangeDimension, range, &callbacks);
 
	// Create the shading object
	CGShadingRef shading = CGShadingCreateAxial(colorSpace, CGPointMake(1, rect.size.height), CGPointMake(1, rect.size.height*0.75f), function, YES, YES);
 
	// Draw the shading
	CGContextDrawShading(context, shading);
 
	// Clean up
	CGFunctionRelease(function);
	CGShadingRelease(shading);
	CGColorSpaceRelease(colorSpace);
}
 
// This is the callback of our shading function.
static void blackShade(void *info, const CGFloat *inData, CGFloat *outData) {
	float p = inData[0];
	outData[0] = 0.0f;
	outData[1] = (1.0f-slope(p, 2.0f)) * 0.5f;
}
 
// ristributes values on a slope (ease-in ease-out)
static float slope(float x, float A) {
	float p = powf(x, A);
	return p/(p + powf(1.0f-x, A));
}

Hello Jernej,
I tried to reach you out on Twitter but I guess that talking here is more appropriate. I've been looking for a smooth gradient solution for days and then I found your article just about a few hours ago but, being a junior developer, and your code is pretty complicated for me to understand! I needed to create a smooth gradient that goes from a transparent color to whatever color I need. I tried editing your code (tried using CGColorSpaceCreateDeviceRGB()) without success. Could you help me out? I would appreciate that so much.

Luca