Glowing.m

//
//  UIView+UIView_glow.m
//  Hab It!
//
//  Created by orkenstein on 30.09.14.
//  Copyright (c) 2014 savefon.mobi. All rights reserved.
//

#import "UIView+glow.h"
#import <DProperty/DPPPropertyAttribute.h>

@interface GlowLayer : CALayer

@property (nonatomic, assign) CGFloat glowSize;
@property (nonatomic, strong) UIColor *glowColor;
@property (nonatomic, assign) CGFloat innerGlowSize;
@property (nonatomic, strong) UIColor *innerGlowColor;
@property (nonatomic, assign) UIView *parentView;

@end

@interface UIView (glow_private)
@property (nonatomic, strong) GlowLayer *glowLayer;
@property (nonatomic, assign) BOOL glowHiddenPrivate;

@end

@implementation UIView (glow_private)

@dynamic glowHiddenPrivate;
@dynamic glowLayer;

@end

@implementation UIView (glow)

@dynamic glowSize;
@dynamic glowColor;
@dynamic innerGlowSize;
@dynamic innerGlowColor;

- (void)setGlowHidden:(BOOL)glowHidden {
  self.layer.masksToBounds = glowHidden;
  self.clipsToBounds = glowHidden;
  if (self.glowLayer == nil) {
    self.glowLayer = [GlowLayer layer];
    self.glowLayer.frame = self.layer.bounds;
    self.glowLayer.parentView = self;
    self.glowLayer.masksToBounds = NO;
    self.glowLayer.contentsGravity = kCAGravityCenter;
    [self.layer addSublayer:self.glowLayer];
  }
  self.glowLayer.glowSize = self.glowSize;
  self.glowLayer.glowColor = self.glowColor;
  self.glowLayer.innerGlowSize = self.innerGlowSize;
  self.glowLayer.innerGlowColor = self.innerGlowColor;
  self.glowLayer.hidden = glowHidden;
  self.glowHiddenPrivate = glowHidden;
  [self.glowLayer setNeedsDisplay];
  [self.glowLayer performSelector:@selector(setNeedsDisplay) withObject:nil afterDelay:0.0];
}

- (BOOL)glowHidden {
  return self.glowHiddenPrivate;
}

@end

@implementation GlowLayer

+ (instancetype)layer {
  GlowLayer *layer = [super layer];
  layer.contentsScale = [[UIScreen mainScreen] scale];

  return layer;
}

- (void)drawInContext:(CGContextRef)ctx {
  CGFloat delta = MAX(self.glowSize, self.innerGlowSize);
  CGRect drawingRect = CGRectMake(-delta, -delta, CGRectGetWidth(self.parentView.frame) + 2 * delta,
                                  CGRectGetHeight(self.parentView.frame) + 2 * delta);
  CGPoint offsetPoint = CGPointMake(-drawingRect.origin.x, -drawingRect.origin.y);
  self.frame = drawingRect;
  [self setNeedsLayout];
  [self layoutIfNeeded];

  UIGraphicsBeginImageContextWithOptions(drawingRect.size, NO, 0.0f);

//  [self.parentView drawViewHierarchyInRect:rect afterScreenUpdates:YES];
  [self.parentView.layer renderInContext:UIGraphicsGetCurrentContext()];
  UIImage *textImage = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();

  UIGraphicsPushContext(ctx);
  CGContextSaveGState(ctx);
  if (_glowSize > 0) {
    CGContextSetShadow(ctx, CGSizeZero, _glowSize);
    CGContextSetShadowWithColor(ctx, CGSizeZero, _glowSize, _glowColor.CGColor);
  }
  [textImage drawAtPoint:offsetPoint];

  CGContextRestoreGState(ctx);

  if (_innerGlowSize > 0) {
    UIGraphicsBeginImageContextWithOptions(drawingRect.size, NO, 0.0f);
    CGContextRef ctx2 = UIGraphicsGetCurrentContext();
    CGContextSaveGState(ctx2);
    CGContextSetFillColorWithColor(ctx2, [UIColor blackColor].CGColor);
    CGContextFillRect(ctx2, drawingRect);
    CGContextTranslateCTM(ctx2, 0.0, drawingRect.size.height);
    CGContextScaleCTM(ctx2, 1.0, -1.0);
    CGContextClipToMask(ctx2, drawingRect, textImage.CGImage);
    CGContextClearRect(ctx2, drawingRect);
    CGContextRestoreGState(ctx2);

    UIImage *inverted = UIGraphicsGetImageFromCurrentImageContext();
    CGContextClearRect(ctx2, drawingRect);

    CGContextSaveGState(ctx2);
    CGContextSetFillColorWithColor(ctx2, _innerGlowColor.CGColor);
    CGContextSetShadowWithColor(ctx2, CGSizeZero, _innerGlowSize, _innerGlowColor.CGColor);
    [inverted drawAtPoint:CGPointZero];
    CGContextTranslateCTM(ctx2, 0.0, drawingRect.size.height);
    CGContextScaleCTM(ctx2, 1.0, -1.0);
    CGContextClipToMask(ctx2, drawingRect, inverted.CGImage);
    CGContextClearRect(ctx2, drawingRect);
    CGContextRestoreGState(ctx2);

    UIImage *innerShadow = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();
    [innerShadow drawAtPoint:offsetPoint];
  }

//  textImage = UIGraphicsGetImageFromCurrentImageContext();
//  self.contents = (id)textImage.CGImage;
}

@end