SAMCubicSpline
I found this math somewhere and tweaked it some to work the way I needed it. A cubic spline is great for drawing the curve in a tone curve filter.
Installation
Simply add the following to your Podfile:
pod 'SAMCubicSpline'If you're not using CocoaPods, simply add the source files in the SAMCubicSpline directory to your project. There are no dependencies and it works on Mac and iOS.
Example
A quick sample to draw a spline into an already setup CGContextRef and assumes you'll finish drawing the line at the end.
#import "SAMCubicSpline.h"
// Setup a spline with some control points
#if TARGET_OS_IOS
SAMCubicSpline *spline = [[SAMCubicSpline alloc] initWithPoints:@[
[NSValue valueWithCGPoint:CGPointMake(0.0f, 0.039f)],
[NSValue valueWithCGPoint:CGPointMake(0.588f, 0.525f)],
[NSValue valueWithCGPoint:CGPointMake(1.0f, 1.0f)],
]];
#else
SAMCubicSpline *spline = [[SAMCubicSpline alloc] initWithPoints:@[
[NSValue valueWithPoint:CGPointMake(0.0f, 0.039f)],
[NSValue valueWithPoint:CGPointMake(0.588f, 0.525f)],
[NSValue valueWithPoint:CGPointMake(1.0f, 1.0f)],
]];
#endif
// Iterate over the X values in the area we want to draw
CGSize graphSize = CGSizeMake(100.0f, 100.0f);
for (CGFloat x = 0.0f; x < size.width; x++) {
// Get the Y value of our point
CGFloat y = [spline interpolate:x / size.width] * size.height;
// Add the point to the context's path
if (x == 0.0f) {
CGContextMoveToPoint(context, x, y);
} else {
CGContextAddLineToPoint(context, x, y);
}
}Thanks
This was abstracted from Footage. Thanks to Drew Wilson for allowing me to open source this!