I'm currently drawing a line using Core Graphics. It's really bare bones and simple.
- (void)drawRect:(CGRect)rect {
CGContextRef c = UIGraphicsGetCurrentContext();
CGFloat red[4] = {1.0f, 0.0f, 0.0f, 1.0f};
CGContextSetStrokeColor(c, red);
CGContextBeginPath(c);
CGContextMoveToPoint(c, 5.0f, 5.0f);
CGContextAddLineToPoint(c, 300.0f, 600.0f);
CGContextSetLineWidth(c, 25);
CGContextSetLineCap(c, kCGLineCapRound);
CGContextStrokePath(c);
}
This works well. Let's say that we wanted to draw a custom style line. Say we wanted to imitate the style of a crayon for example. And that the designer handed your crayon style images: http://imgur.com/a/N40ig
To do accomplish this effect I think I need to do something like this:
Create a special colored versions of crayonImage1-crayonImage4
Every time you add a line to line you use one of the crayonImages
You alternate the crayonImages every time you draw a point.
Step 1 makes sense. I can use the following method:
- (UIImage *)image:(UIImage *)img withColor:(UIColor *)color {
// begin a new image context, to draw our colored image onto
UIGraphicsBeginImageContext(img.size);
// get a reference to that context we created
CGContextRef context = UIGraphicsGetCurrentContext();
// set the fill color
[color setFill];
// translate/flip the graphics context (for transforming from CG* coords to UI* coords
CGContextTranslateCTM(context, 0, img.size.height);
CGContextScaleCTM(context, 1.0, -1.0);
// set the blend mode to color burn, and the original image
CGContextSetBlendMode(context, kCGBlendModeColorBurn);
CGRect rect = CGRectMake(0, 0, img.size.width, img.size.height);
CGContextDrawImage(context, rect, img.CGImage);
// set a mask that matches the shape of the image, then draw (color burn) a colored rectangle
CGContextClipToMask(context, rect, img.CGImage);
CGContextAddRect(context, rect);
CGContextDrawPath(context,kCGPathFill);
// generate a new UIImage from the graphics context we drew onto
UIImage *coloredImg = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
//return the color-burned image
return coloredImg;
}
I'm unsure how I can complete steps 2 and 3. Is there an API in CoreGraphics for setting an image as the point of line? If so what is it and how can I use it?
Thanks in advance,
-David
Start with the following example: http://www.ifans.com/forums/showthread.php?t=132024
But for brushes, don't draw a line. Simply draw the brush image using CGContextDrawImage.
Basically, you simply draw an image for every touch.
The above is a UITableViewCell containing two UILabels. The cell has a transparent background using [UIColor clearColor] and the background pattern (you may need to look closely to see it) is set on the UITableView using UIColor's initWithPatternImage.
What I'd like to be able to do is blend the text with the background pattern so that the text has the texture coming through. The only thing is I'm not sure of is the best way of achieving this.
I know I can use NSString instead of UILabels and draw the text directly into an image, but can this then be blended with the background even though it's not being drawn in the same drawRect (i.e. the text image would be drawn in a subclass of UITableViewCell where as the background is being drawn by the UITableView instance)?
The other way is to create an image mask from the text, have another image which is already textured (with the top half white and the bottom half dark grey) and then use that to draw the text, as outlined in this Cocoa with Love tutorial.
Whilst I can obviously use the tutorial to achieve the second implementation, I'm more inclined to explore the first as it'd use no external images and may be more efficient.
Your thoughts, links and code examples will be greatly appreciated.
Please Note: Setting a low alpha value on the UILabels does not achieve the desired effect
If you set the labels as non opaque and an alpha value less than 1.0 it should work. These can be set in either Interface Builder or as code like this:
[theIncidentLabel setOpaque:NO];
[theIncidentLabel setAlpha:0.5];
You can even just set the text color to a color with an alpha value less than 1.0.
[theIncidentLabel setTextColor:[UIColor colorWithRed:1.0 green:1.0 blue:1.0 alpha:0.5]];
Using these settings I do see the background texture through labels in a project I'm working on. In my project the list UITableView is also transparent, and the background texture comes from an image loaded in a UIImageView behind the UITableView.
This is simple alpha blending. We figured out through a discussion in comments that this is inadequate for your needs. Instead you can use the alpha masking as explained in the tutorial mentioned.
Alternatively, you could forgo alpha masks and just draw the text to a CGImage, then draw that image on your background pattern with a different blend mode, maybe kCGBlendModeScreen. Here's the drawRect method from the above mentioned tutorial rewritten with this technique:
- (void)drawRect:(CGRect)rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
// Draw a black background
[[UIColor blackColor] setFill];
CGContextFillRect(context, rect);
// Draw the text upside-down
CGContextSaveGState(context);
CGContextTranslateCTM(context, 0, rect.size.height);
CGContextScaleCTM(context, 1.0, -1.0);
[[UIColor lightGrayColor] setFill];
[text drawInRect:rect withFont:[UIFont fontWithName:#"HelveticaNeue-Bold" size:40.0]];
// Draw it again in a darker color.
[[UIColor darkGrayColor] setFill];
CGContextTranslateCTM(context, 0, 50.0);
[text drawInRect:rect withFont:[UIFont fontWithName:#"HelveticaNeue-Bold" size:40.0]];
CGContextRestoreGState(context);
// Create an text image from what we've drawn so far
CGImageRef textImage = CGBitmapContextCreateImage(context);
// Draw a white background (overwriting the previous work)
[[UIColor whiteColor] setFill];
CGContextFillRect(context, rect);
// Draw the background image
CGContextSaveGState(context);
[[UIImage imageNamed:#"shuttle.jpg"] drawInRect:rect];
// Set the blend mode. Try different options to meet your tastes.
CGContextSetBlendMode(context, kCGBlendModeScreen);
// Draw the text.
CGContextDrawImage(context, rect, textImage);
// Clean up.
CGContextRestoreGState(context);
CGImageRelease(textImage);
}
I know it's possible to tint a rectangular image by drawing a CGContextFillRect over it and setting the blend mode. However, I can't figure out how to do a tint on a transparent image such as an icon. It must be possible since the SDK does it itself on tab-bars in such. Would anyone be able to provide a snippet?
UPDATE:
Lots of great suggestions have been given for this problem since I originally asked. Be sure to read through all the answers to figure out what suits you best.
UPDATE (Apr 30, 2015):
With iOS 7.0, I can now just do the following, which would satisfy the needs of my original question. But if you have more complicated cases, check out all the answers.
UIImage *iconImage = [[UIImage imageNamed:#"myImageName"] imageWithRenderingMode:UIImageRenderingModeAlwaysTemplate];
UIImageView *icon = [[UIImageView alloc] initWithImage:iconImage];
icon.tintColor = [UIColor redColor];
Update: Here is a Gist for a Swift UIColor extension using the code below.
If you have a greyscale image and want white become the tinting color, kCGBlendModeMultiply is the way to go. With this method, you cannot have highlights lighter than your tinting color.
On the contrary, if you have either a non-greyscale image, OR you have highlights and shadows that should be preserved, the blend mode kCGBlendModeColor is the way to go. White will stay white and black will stay black as the lightness of the image is preserved. This mode is just made for tinting - it is the same as Photoshop's Color layer blend mode (disclaimer: slightly differing results may happen).
Note that tinting alpha-pixels does not work correctly neither in iOS nor in Photoshop - half-transparent black pixels would not stay black. I updated the answer below to work around that issue, it took quite a long time to find out.
You can also use one of the blend modes kCGBlendModeSourceIn/DestinationIn instead of CGContextClipToMask.
If you want to create a UIImage, each of the following code sections can be surrounded by the following code:
UIGraphicsBeginImageContextWithOptions (myIconImage.size, NO, myIconImage.scale); // for correct resolution on retina, thanks #MobileVet
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextTranslateCTM(context, 0, myIconImage.size.height);
CGContextScaleCTM(context, 1.0, -1.0);
CGRect rect = CGRectMake(0, 0, myIconImage.size.width, myIconImage.size.height);
// image drawing code here
UIImage *coloredImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
So here's the code for tinting a transparent image with kCGBlendModeColor:
// draw black background to preserve color of transparent pixels
CGContextSetBlendMode(context, kCGBlendModeNormal);
[[UIColor blackColor] setFill];
CGContextFillRect(context, rect);
// draw original image
CGContextSetBlendMode(context, kCGBlendModeNormal);
CGContextDrawImage(context, rect, myIconImage.CGImage);
// tint image (loosing alpha) - the luminosity of the original image is preserved
CGContextSetBlendMode(context, kCGBlendModeColor);
[tintColor setFill];
CGContextFillRect(context, rect);
// mask by alpha values of original image
CGContextSetBlendMode(context, kCGBlendModeDestinationIn);
CGContextDrawImage(context, rect, myIconImage.CGImage);
If your image has no half-transparent pixels, you could also do it the other way around with kCGBlendModeLuminosity:
// draw tint color
CGContextSetBlendMode(context, kCGBlendModeNormal);
[tintColor setFill];
CGContextFillRect(context, rect);
// replace luminosity of background (ignoring alpha)
CGContextSetBlendMode(context, kCGBlendModeLuminosity);
CGContextDrawImage(context, rect, myIconImage.CGImage);
// mask by alpha values of original image
CGContextSetBlendMode(context, kCGBlendModeDestinationIn);
CGContextDrawImage(context, rect, myIconImage.CGImage);
If you don't care for luminosity, as you just have got an image with an alpha channel that should be tinted with a color, you can do it in a more efficient way:
// draw tint color
CGContextSetBlendMode(context, kCGBlendModeNormal);
[tintColor setFill];
CGContextFillRect(context, rect);
// mask by alpha values of original image
CGContextSetBlendMode(context, kCGBlendModeDestinationIn);
CGContextDrawImage(context, rect, myIconImage.CGImage);
or the other way around:
// draw alpha-mask
CGContextSetBlendMode(context, kCGBlendModeNormal);
CGContextDrawImage(context, rect, myIconImage.CGImage);
// draw tint color, preserving alpha values of original image
CGContextSetBlendMode(context, kCGBlendModeSourceIn);
[tintColor setFill];
CGContextFillRect(context, rect);
Have fun!
I had most success with this method, because the others I tried caused distorted colors for semi-transparent pixels for certain color-combinations. This should also be a bit better on the performance side.
+ (UIImage *) imageNamed:(NSString *) name withTintColor: (UIColor *) tintColor {
UIImage *baseImage = [UIImage imageNamed:name];
CGRect drawRect = CGRectMake(0, 0, baseImage.size.width, baseImage.size.height);
UIGraphicsBeginImageContextWithOptions(baseImage.size, NO, 0);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextTranslateCTM(context, 0, baseImage.size.height);
CGContextScaleCTM(context, 1.0, -1.0);
// draw original image
CGContextSetBlendMode(context, kCGBlendModeNormal);
CGContextDrawImage(context, drawRect, baseImage.CGImage);
// draw color atop
CGContextSetFillColorWithColor(context, tintColor.CGColor);
CGContextSetBlendMode(context, kCGBlendModeSourceAtop);
CGContextFillRect(context, drawRect);
UIImage *tintedImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return tintedImage;
}
After searching around, the best solution I've come to thus far is to use a combination of blend mode and the clipping mask to achieve colorizing/tinting a transparent PNG:
CGContextSetBlendMode (context, kCGBlendModeMultiply);
CGContextDrawImage(context, rect, myIconImage.CGImage);
CGContextClipToMask(context, rect, myIconImage.CGImage);
CGContextSetFillColorWithColor(context, tintColor);
CGContextFillRect(context, rect);
I can get results very close to the tint in the Apple navigation bar by using kCGBlendModeOverlay. Taking excelent #fabb answer and combining #omz approach in this post https://stackoverflow.com/a/4684876/229019 I came with this solution that helds the results I was expecting:
- (UIImage *)tintedImageUsingColor:(UIColor *)tintColor;
{
UIGraphicsBeginImageContextWithOptions (self.size, NO, [[UIScreen mainScreen] scale]);
CGContextRef context = UIGraphicsGetCurrentContext();
CGRect rect = CGRectMake(0, 0, self.size.width, self.size.height);
// draw original image
[self drawInRect:rect blendMode:kCGBlendModeNormal alpha:1.0f];
// tint image (loosing alpha).
// kCGBlendModeOverlay is the closest I was able to match the
// actual process used by apple in navigation bar
CGContextSetBlendMode(context, kCGBlendModeOverlay);
[tintColor setFill];
CGContextFillRect(context, rect);
// mask by alpha values of original image
[self drawInRect:rect blendMode:kCGBlendModeDestinationIn alpha:1.0f];
UIImage *tintedImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return tintedImage;
}
Here's an example tinting several grayscale images with transparency:
:
The first line is the apple toolbar tinted [UIColor orangeColor].
The second line is the same gradient tinted in several colors starting with clear color (= the actual gradient) and ending with the same orange.
The third is a simple circle with transparency (the linen is the background color)
The forth line is a complex dark noisy texture
You could create an UIImage category and do it like this:
- (instancetype)tintedImageWithColor:(UIColor *)tintColor {
UIGraphicsBeginImageContextWithOptions(self.size, NO, 0.0);
CGContextRef context = UIGraphicsGetCurrentContext();
CGRect rect = (CGRect){ CGPointZero, self.size };
CGContextSetBlendMode(context, kCGBlendModeNormal);
[self drawInRect:rect];
CGContextSetBlendMode(context, kCGBlendModeSourceIn);
[tintColor setFill];
CGContextFillRect(context, rect);
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;
}
In iOS7, they've introduced tintColor property on UIImageView and renderingMode on UIImage. See my example at https://stackoverflow.com/a/19125120/1570970
With iOS 7.0, you can also just do this to tint a basic UIImageView:
UIImage *iconImage = [[UIImage imageNamed:#"myImageName"] imageWithRenderingMode:UIImageRenderingModeAlwaysTemplate];
UIImageView *icon = [[UIImageView alloc] initWithImage:iconImage];
icon.tintColor = [UIColor redColor];
Note that in the accepted answer by fabb, the "surrounding" code for making a UIImage gave me the wrong resolution of images on retina screen. To fix, change:
UIGraphicsBeginImageContext(myIconImage.size);
to:
UIGraphicsBeginImageContextWithOptions(myIconImage.size, NO, 0.0);
The last parameter which is set to 0.0 is scale, and according to Apple documentation:
"If you specify a value of 0.0, the scale factor is set to the scale
factor of the device’s main screen".
Dont have the permission to comment, and editing seems a bit rude, so I mention this in an answer.
Just in case someone encounters this same problem.
UIImageView (or any view for that matter) has a background color which is RGBA. The alpha in the color may do what you need without inventing something new.
Not my work, but i've successfully used this approach:
http://coffeeshopped.com/2010/09/iphone-how-to-dynamically-color-a-uiimage
I wanted to shade my image views in my custom UIButton subclass and the other solutions didn't do what I wanted. I needed to darken "tint" the image color. Here's how to change the brightness using CoreImage.
Make sure you add CoreImage.framework to your project's libraries. (Link Binary with Libraries)
UIImage shade method
- (UIImage *)shadeImage:(UIImage *)image {
CIImage *inputImage = [CIImage imageWithCGImage:image.CGImage];
CIContext *context = [CIContext contextWithOptions:nil];
CIFilter *filter = [CIFilter filterWithName:#"CIColorControls"
keysAndValues:kCIInputImageKey, inputImage,
#"inputBrightness", [NSNumber numberWithFloat:-.5], nil];
CIImage *outputImage = [filter outputImage];
CGImageRef cgImage = [context createCGImage:outputImage fromRect:[outputImage extent]];
UIImage *newImage = [UIImage imageWithCGImage:cgImage scale:image.scale orientation:image.imageOrientation];
CGImageRelease(cgImage);
return newImage;
}
You'll want to store a copy of the context as an ivar, rather than recreate it.
No answers will help me on stack overflow: our designers draw UI elements with various forms, various alpha values (and "alpha-holes"). In most cases, this is 32-Bit PNG file with alpha channel, which comprises black & white pixels (of all possible intensities). After tinting such a picture I had to get this tinted result: white pixels - tinted over more, and dark pixels - less. And all this in view of alpha channel. And i wrote this method for my UIImage category. Maybe it not high efficient, but it work as clock:) Here it is:
- (UIImage *)imageTintedWithColor:(UIColor *)color {
UIGraphicsBeginImageContextWithOptions(self.size, NO, self.scale);
CGContextRef context = UIGraphicsGetCurrentContext();
CGRect rect = CGRectMake(0, 0, self.size.width, self.size.height);
CGContextSetBlendMode(context, kCGBlendModeCopy);
[color setFill];
CGContextFillRect(context, rect);
[self drawInRect:rect blendMode:kCGBlendModeXOR alpha:1.0];
CGContextSetBlendMode(context, kCGBlendModeXOR);
CGContextFillRect(context, rect);
[self drawInRect:rect blendMode:kCGBlendModeMultiply alpha:1.0];
UIImage *coloredImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return coloredImage;
}
First I want to thank fabb for his exceptional solution which has helped me to accomplish my task to tint half transparent Icons. Because I needed a solution for C# (Monotouch) I had to translate his code. Here is what I came up with. Just copy paste this into your code and add your half transparent Image and your done.
So again all credits go to fabb. This is just to kick start C# users :)
//TINT COLOR IMAGE
UIImageView iImage = new UIImageView(new RectangleF(12, 14, 24,24));
iImage.ContentMode = UIViewContentMode.ScaleAspectFit;
iImage.Image = _dataItem.Image[0] as UIImage;
UIGraphics.BeginImageContextWithOptions(iImage.Bounds.Size, false, UIScreen.MainScreen.Scale);
CGContext context = UIGraphics.GetCurrentContext();
context.TranslateCTM(0, iImage.Bounds.Size.Height);
context.ScaleCTM(1.0f, -1.0f);
RectangleF rect = new RectangleF(0,0, iImage.Bounds.Width, iImage.Bounds.Height);
// draw black background to preserve color of transparent pixels
context.SetBlendMode(CGBlendMode.Normal);
UIColor.Black.SetFill();
context.FillRect(rect);
// draw original image
context.SetBlendMode(CGBlendMode.Normal);
context.DrawImage(rect, iImage.Image.CGImage);
// tint image (loosing alpha) - the luminosity of the original image is preserved
context.SetBlendMode(CGBlendMode.Color);
UIColor.Orange.SetFill();
context.FillRect(rect);
// mask by alpha values of original image
context.SetBlendMode(CGBlendMode.DestinationIn);
context.DrawImage(rect, iImage.Image.CGImage);
UIImage coloredImage = UIGraphics.GetImageFromCurrentImageContext();
UIGraphics.EndImageContext();
iImage = new UIImageView(coloredImage);
iImage.Frame = new RectangleF(12, 14, 24,24);
//END TINT COLOR IMAGE
cell.Add(iImage);
I'm using a CAShapeLayer with a path. Now I want it to throw a smooth shadow with about 10 units of thickness.
First: Yeah, I could create just 11 CAShapeLayer objects and each time increase the outline of the path by 1 unit with an different color and some more alpha on every iteration. But this way I blow up my memory footprint since the thing is half screen size and this would mean to have 11x a bitmap of half screen size in memory.
So since iPhone OS 3.2 I could probably use those nifty shadow properties on CALayer. But I want to stick to OS 3.0. So what options do I have, other than the nasty one above?
You could create the shadow using Core Graphics. The building blocks you'll need are described in QuartzDemo sample. In particular have a look at class QuartzMaskingView in QuartzClipping.m.
Capture the content of the shape layer into image
Set the shadow to your liking
Begin transparency layer
Clip to the image of layers content - you'll be drawing outside of it
Draw your image again
This results in shadow being painted outside of your masked area.
CGSize size = CGSizeMake(300, 100);
UIGraphicsBeginImageContextWithOptions(size,NO, 0.0);
[shapeLayer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
CGRect flippedImageRect =
CGRectMake(0, 0, image.size.width, -image.size.height);
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextSaveGState(ctx);
CGContextSetShadowWithColor(ctx, CGSizeMake(4, 4), 2,
[[UIColor colorWithWhite:0 alpha:0.4] CGColor]);
CGContextBeginTransparencyLayer(ctx, NULL);
CGContextScaleCTM(ctx, 1.0, -1.0);
CGContextClipToMask(ctx, flippedImageRect, [image CGImage]);
CGContextSetFillColorWithColor(ctx, [[UIColor redColor] CGColor]);
CGContextDrawImage(ctx, flippedImageRect, [image CGImage]);
CGContextEndTransparencyLayer(ctx);
CGContextRestoreGState(ctx);