PFColorLiteSlider.m

#import "PFColorLiteSlider.h"
#import "UIColor+PFColor.h"

@interface PFColorSliderBackgroundView : UIView
@property (nonatomic, retain) UIColor *color;
@property (nonatomic, assign) CGFloat hue;
@property (assign) PFSliderBackgroundStyle style;
- (id)initWithFrame:(CGRect)frame
              color:(UIColor *)color
              style:(PFSliderBackgroundStyle)style;
@end

@implementation PFColorSliderBackgroundView

- (id)initWithFrame:(CGRect)frame
              color:(UIColor *)color
              style:(PFSliderBackgroundStyle)style {
    self = [super initWithFrame:frame];
    self.color = color;
    self.style = style;
    self.backgroundColor = [UIColor clearColor];

    return self;
}

- (void)setColor:(UIColor *)color {
    _color = color;
    self.hue = color.hue;
}

- (void)drawRect:(CGRect)rect {
    CGContextRef context = UIGraphicsGetCurrentContext();

    for (int x = 0; x < rect.size.width; x++) {
        float percent = 100 - (rect.size.width - x) / rect.size.width * 100.f;

        if (self.style == PFSliderBackgroundStyleSaturation)
            [[UIColor colorWithHue:self.hue
                        saturation:(percent / 100)
                        brightness:1 
                             alpha:1] setFill];
        else if (self.style == PFSliderBackgroundStyleBrightness)
            [[UIColor colorWithHue:self.hue
                        saturation:1
                        brightness:(percent / 100)
                             alpha:1] setFill];
        else if (self.style == PFSliderBackgroundStyleAlpha)
            [[UIColor colorWithHue:self.hue
                        saturation:self.color.saturation
                        brightness:self.color.brightness 
                             alpha:(percent / 100)] setFill];

        CGContextFillRect(context, CGRectMake(x, 0, 1, rect.size.height));
    }
}

@end


@interface UISlider (Private)
- (UIView *)_minTrackView;
- (UIView *)_maxTrackView;
@end

@interface PFSlider : UISlider
@end

@implementation PFSlider

- (void)layoutSubviews {
    [super layoutSubviews];

    [self _minTrackView].hidden = YES;
    [self _maxTrackView].hidden = YES;
}

@end


@interface PFColorLiteSlider ()
@property (nonatomic, retain) PFColorSliderBackgroundView *backgroundView;
@property (assign) PFSliderBackgroundStyle style;
@end

@implementation PFColorLiteSlider {
    UIColor *_tintColor;
}

- (id)initWithFrame:(CGRect)frame
              color:(UIColor *)color
          tintColor:(UIColor *)tintColor
              style:(PFSliderBackgroundStyle)style {
    self = [super initWithFrame:frame];

    self.style = style;
    _tintColor = tintColor;

    CGRect internalFrame = CGRectMake(0, 0, frame.size.width, frame.size.height);
    self.slider = [[PFSlider alloc] initWithFrame:internalFrame];
    self.slider.minimumValue = 0.0000001f;
    self.slider.maximumValue = 1.0;

    internalFrame.size.height = 10; // Set to ten because we want a thin BG
    internalFrame.origin.y = (frame.size.height - 10) / 2;
    self.backgroundView = [[PFColorSliderBackgroundView alloc] initWithFrame:internalFrame
                                                                       color:color
                                                                       style:style];
    self.backgroundView.layer.cornerRadius = 5;
    self.backgroundView.layer.masksToBounds = YES;

    [self addSubview:self.backgroundView];
    [self addSubview:self.slider];

    [self updateGraphicsWithColor:color];

    return self;
}

- (void)updateGraphicsWithColor:(UIColor *)color {
    [self updateGraphicsWithColor:color hue:color.hue];
}

- (void)updateGraphicsWithColor:(UIColor *)color hue:(CGFloat)hue {
    /* The hue parameter is used since UIColor
       defaults the hue to 0 if there is no saturation. */
    UIColor *modifiedColor;
    if (self.style == PFSliderBackgroundStyleSaturation)
        modifiedColor = [UIColor colorWithHue:hue
                                   saturation:color.saturation
                                   brightness:1
                                        alpha:1];
    else if (self.style == PFSliderBackgroundStyleBrightness)
        modifiedColor = [UIColor colorWithHue:hue
                                   saturation:1
                                   brightness:color.brightness
                                        alpha:1];
    else // PFSliderBackgroundStyleAlpha
        modifiedColor = [UIColor colorWithHue:hue
                                   saturation:color.saturation
                                   brightness:color.brightness
                                        alpha:color.alpha];
    [self.slider setThumbImage:[self thumbImageWithColor:modifiedColor]
                      forState:UIControlStateNormal];

    self.slider.maximumTrackTintColor = [UIColor clearColor];
    self.slider.minimumTrackTintColor = [UIColor clearColor];

    self.backgroundView.color = color;
    self.backgroundView.hue = hue;
    [self.backgroundView setNeedsDisplay];

    if (self.style == PFSliderBackgroundStyleSaturation)
        self.slider.value = color.saturation;
    else if (self.style == PFSliderBackgroundStyleBrightness)
        self.slider.value = color.brightness;
    else if (self.style == PFSliderBackgroundStyleAlpha)
        self.slider.value = color.alpha;
}

- (UIImage *)thumbImageWithColor:(UIColor *)color {
    CGFloat size = 36.0f;
    CGRect rect = CGRectMake(0.0f, 0.0f, size, size);
    UIGraphicsBeginImageContextWithOptions(rect.size, NO, [UIScreen mainScreen].scale);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetLineWidth(context, 3.5);

    CGFloat red, green, blue;
    [_tintColor getRed:&red green:&green blue:&blue alpha:nil];
    CGContextSetRGBStrokeColor(context, red, green, blue, 0.4f);

    CGContextAddArc(context, rect.size.width / 2, rect.size.height / 2, rect.size.width / 3, 0, 2 * M_PI, 1);
    CGContextDrawPath(context, kCGPathStroke);

    CGContextAddArc(context, rect.size.width / 2, rect.size.height / 2, rect.size.width / 3 - 1, 0, 2 * M_PI, 1);
    CGContextSetFillColorWithColor(context, color.CGColor);
    CGContextDrawPath(context, kCGPathEOFill);

    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return image;
}

@end