Questions tagged [core-graphics]
Core Graphics is Apple's framework for low-level drawing operations on Mac OS X and iOS.
core-graphics
5,988
questions
358
votes
16
answers
258k
views
How do I draw a shadow under a UIView?
I'm trying to draw a shadow under the bottom edge of a UIView in Cocoa Touch. I understand that I should use CGContextSetShadow() to draw the shadow, but the Quartz 2D programming guide is a little ...
- 4,642
219
votes
26
answers
87k
views
invalid context 0x0 under iOS 7.0 and system degradation
I've read as many search results I could find on this dreaded problem, unfortunatelly, each one seems to focus on a specific function call.
My problem is that I get the same error from multiple ...
- 14.6k
205
votes
11
answers
151k
views
How to get pixel data from a UIImage (Cocoa Touch) or CGImage (Core Graphics)?
I have a UIImage (Cocoa Touch). From that, I'm happy to get a CGImage or anything else you'd like that's available. I'd like to write this function:
- (int)getRGBAFromImage:(UIImage *)image atX:(int)...
- 24.7k
190
votes
17
answers
124k
views
UIImage: Resize, then Crop
I've been bashing my face into this one for literally days now and even though I feel constantly that I am right on the edge of revelation, I simply cannot achieve my goal.
I thought, ahead of time ...
- 2,372
187
votes
18
answers
127k
views
CGContextDrawImage draws image upside down when passed UIImage.CGImage
Does anyone know why CGContextDrawImage would be drawing my image upside down? I am loading an image in from my application:
UIImage *image = [UIImage imageNamed:@"testImage.png"];
And then simply ...
- 45k
186
votes
8
answers
9k
views
Draw a perfect circle from user's touch
I have this practice project that allows the user to draw on the screen as they touch with their fingers. Very simple App I did as an exercise way back.
My little cousin took the liberty of drawing ...
- 16.2k
184
votes
19
answers
192k
views
How to Rotate a UIImage 90 degrees?
I have a UIImage that is UIImageOrientationUp (portrait) that I would like to rotate counter-clockwise by 90 degrees (to landscape). I don't want to use a CGAffineTransform. I want the pixels of the ...
- 14k
151
votes
19
answers
63k
views
Get Slightly Lighter and Darker Color from UIColor
I was looking to be able to turn any UIColor into a gradient. The way I am intending to do this is by using Core Graphics to draw a gradient. What I am trying to do is to get a color, lets say:
[...
- 2,227
143
votes
4
answers
19k
views
to drawRect or not to drawRect (when should one use drawRect/Core Graphics vs subviews/images and why?)
To clarify the purpose of this question: I know HOW to create complicated views with both subviews and using drawRect. I'm trying to fully understand the when's and why's to use one over the other.
I ...
- 17.8k
140
votes
8
answers
82k
views
How to control shadow spread and blur?
I have designed UI elements in sketch, and one of them has a shadow with blur 1 and spread 0. I looked at the doc for the views layer property and layer doesn't have anything named spread or blur, or ...
- 3,193
121
votes
6
answers
39k
views
How to create a colored 1x1 UIImage on the iPhone dynamically?
I would like to create a 1x1 UIImage dynamically based on a UIColor.
I suspect this can quickly be done with Quartz2d, and I'm poring over the documentation trying to get a grasp of the fundamentals. ...
- 10.8k
120
votes
15
answers
75k
views
How do I make UILabel display outlined text?
All I want is a one pixel black border around my white UILabel text.
I got as far as subclassing UILabel with the code below, which I clumsily cobbled together from a few tangentially related online ...
- 4,399
114
votes
4
answers
27k
views
How to store CGRect values in NSMutableArray?
How would I store CGRect objects in a NSMutableArray, and then later retrieve them?
113
votes
6
answers
66k
views
iOS 7 style Blur view
Does anybody know of any controls that will replicate the iOS7 style blur views.
I'm assumming there can be some kind of UIView subclass that will replicate the behavior.
I'm talking about these ...
- 3,872
102
votes
8
answers
135k
views
Where can I find a list of Mac virtual key codes?
I'm using CGEventCreateKeyboardEvent and need to know what CGKeyCode values to use.
Specifically, I am after the key code for the Command key. The docs give examples for other keys: z is 6, shift is ...
- 15.7k
95
votes
4
answers
76k
views
How can I set CG_CONTEXT_SHOW_BACKTRACE environmental variable?
I have three buttons in my view. After setting the cornerRadus in the viewDidLoad() : button.layer.cornerRadius = 20 I get the following error message in the log:
<Error>: CGContextSaveGState: ...
user5087998
93
votes
7
answers
44k
views
NSLog with CGPoint data
I have a CGPoint called point that is being assigned a touch:
UITouch *touch = [touches anyObject];
CGPoint point = [touch locationInView:self];
I want to get the x coordinate value into my console ...
- 4,990
92
votes
13
answers
38k
views
Get lighter and darker color variations for a given UIColor
How to get different lighter and darker variations of a given UIColor in Swift?
- 3,405
92
votes
17
answers
86k
views
Inner shadow effect on UIView layer?
I have the following CALayer:
CAGradientLayer *gradient = [CAGradientLayer layer];
gradient.frame = CGRectMake(8, 57, 296, 30);
gradient.cornerRadius = 3.0f;
gradient.colors = [NSArray ...
- 14.9k
91
votes
7
answers
58k
views
How to Convert UIView to PDF within iOS?
There are a lot of resources about how to display a PDF in an App's UIView. What I am working on now is to create a PDF from UIViews.
For example, I have a UIView, with subviews like Textviews, ...
- 3,527
80
votes
6
answers
59k
views
Extracting rgb from UIColor [duplicate]
Seen this asked before but my example does not seem to work.
const CGFloat *toCol = CGColorGetComponents([[UIColor greenColor] CGColor]);
The array is empty from looking at it with GDB. Any hints?
J T
80
votes
5
answers
39k
views
How to draw a smooth circle with CAShapeLayer and UIBezierPath?
I am attempting to draw a stroked circle by using a CAShapeLayer and setting a circular path on it. However, this method is consistently less accurate when rendered to the screen than using ...
- 7,170
79
votes
6
answers
35k
views
iOS: what's the fastest, most performant way to make a screenshot programmatically?
in my iPad app, I'd like to make a screenshot of a UIView taking a big part of the screen. Unfortunately, the subviews are pretty deeply nested, so it takes to long to make the screenshot and animate ...
- 16.9k
79
votes
3
answers
35k
views
What's the difference between Quartz Core, Core Graphics and Quartz 2D?
I wonder if someone can distinguish precisely between these?
For my understanding, Core Graphics is just a "Framework Package" which contains Quartz Core and Quartz 2D. But I'm not sure about if ...
- 40.4k
79
votes
4
answers
34k
views
NSAttributedString background color and rounded corners
I have a question regarding rounded corners and text background color for a custom UIView.
Basically, I need to achieve an effect like this (image attached - notice the rounded corners on one side) ...
- 5,164
77
votes
8
answers
71k
views
How to Convert UIImage to CIImage and vice versa
I'm trying to get CIImage from ImageView that display on the screen.
UIImage *image = myImageView.image;
convert image UIImage to CIImage.
CIImage *cImage = [....];
How to do this?
- 12.3k
77
votes
9
answers
68k
views
How to scale down a UIImage and make it crispy / sharp at the same time instead of blurry?
I need to scale down an image, but in a sharp way. In Photoshop for example there are the image size reduction options "Bicubic Smoother" (blurry) and "Bicubic Sharper".
Is this image downscaling ...
- 40.3k
75
votes
3
answers
34k
views
Draw segments from a circle or donut
I've been trying to figure out a way to draw segments as illustrated in the following image:
I'd like to:
draw the segment
include gradients
include shadows
animate the drawing from 0 to n angle
I'...
- 1,456
74
votes
3
answers
40k
views
Create and export an animated gif via iOS?
I have a series of user-customized images within an iOS app that are being animated in a simple, frame-by-frame flip book style.
My question is this: is there a way to allow users to export their ...
- 1,482
67
votes
2
answers
2k
views
Detecting CGAssociateMouseAndMouseCursorPosition
We're making a user-space device driver for OS X that moves the cursor using Quartz Events, and we ran into a problem when games — especially ones that run in a windowed mode — can't properly capture ...
- 2,365
66
votes
9
answers
84k
views
How to draw a rounded rectangle in Core Graphics / Quartz 2D?
I need to draw an outline for a rounded rectangle. I know I can make lines and arcs, but maybe there is also a function for rounded rects?
- 45.8k
64
votes
6
answers
42k
views
iPhone smooth sketch drawing algorithm
I am working on a sketching app on the iPhone.
I got it working but not pretty as seen here
And I am looking for any suggestion to smooth the drawing
Basically, what I did is when user places a ...
- 1,301
61
votes
7
answers
48k
views
How to merge two UIImages?
I am trying to merge two different images and create a new one. This is the way I would like to do:
I have this image (A):
It's a PNG image and I would like to merge this one with another image (B) ...
- 1,235
59
votes
16
answers
36k
views
Getting a screenshot of a UIScrollView, including offscreen parts
I have a UIScrollView decendent that implements a takeScreenshot method that looks like this:
-(void)takeScreenshot {
CGRect contextRect = CGRectMake(0, 0, 768, 1004);
...
- 16.9k
57
votes
11
answers
53k
views
Rounded Corners only on Top of a UIView
Hi i am searching a clean solution without overwriting drawRect or stuff like that to create a UIView with Rounded corners on the Top of the View. My main problem here is to create variable solution ...
- 1,205
57
votes
1
answer
10k
views
What's the difference and compatibility of CGLayer and CALayer?
I'm confusing CGLayer and CALayer. They look similar, so why are there separate implementations? What's the difference between, and compatibility of, CGLayer and CALayer?
- 84.7k
57
votes
9
answers
40k
views
Problem setting exif data for an image
I'm using the new ImageIO framework in iOS 4.1. I successfully retrieve the exif metadata using the following:
CFDictionaryRef metadataDict = CMGetAttachment(sampleBuffer, ...
- 6,299
56
votes
5
answers
19k
views
How to detect where NaN is passing to CoreGraphics API on Mac OS X 10.9
I have very large graphic Mac app and now I receive a lot of the following messages in Console on 10.9 GM.
<Error>: Error: this application, or a library it uses, has passed an invalid numeric ...
- 930
55
votes
16
answers
72k
views
Create a rectangle with just two rounded corners in swift?
I need to create a rectangle that have just two rounded corners in swift (Objective C code also ok).
At the moment my code is creating two rectangles with
CGPathCreateWithRoundedRect(CGRectMake(0, ...
- 896
55
votes
12
answers
29k
views
Curve text on existing circle
For an application I am building I have drawn 2 circles. One a bit bigger than the other. I want to curve text between those lines, for a circular menu I am building.
I read most stuff about curving ...
- 5,958
55
votes
3
answers
23k
views
Get PDF hyperlinks on iOS with Quartz
I've spent all day trying to get hyperlinks metadata from PDFs in my iPad application.
The CGPDF* APIs are a true nightmare, and the only piece of information I've found on the net about all this is ...
- 10.2k
53
votes
4
answers
71k
views
How do I create a CGRect from a CGPoint and CGSize?
I need to create a frame for a UIImageView from a varying collection of CGSize and CGPoint, both values will always be different depending on user's choices. So how can I make a CGRect form a CGPoint ...
- 25k
53
votes
1
answer
13k
views
What does yellow tinting represent when using "color misaligned images" on iPhone/iOS
so--i switched on "color misaligned images" to improve drawing performance in our app. The documentation states:
Puts a magenta overlay over images
whose source pixels aren't aligned to
...
- 16k
53
votes
1
answer
2k
views
Weak performance of CGEventPost under GPU load
We've stumbled upon a performance problem with Quartz Events, more specifically CGEventPost: during heavy GPU load CGEventPost can block. We've created a small benchmark application to demonstrate the ...
- 2,365
51
votes
1
answer
6k
views
CABasicAnimation does not animate correctly when I update model layer
I'm currently implementing a CABasicAnimation that animates a CALayer transform property.
Now, although I'm new to Core Animation, I have been able to gather through various blogs and articles such as ...
- 565
49
votes
1
answer
3k
views
How to use kCGImagePropertyGIFImageColorMap or create a color table?
I'm trying to tinker with a couple GIF properties such as kCGImagePropertyGIFImageColorMap and kCGImagePropertyGIFHasGlobalColorMap (reference) in Core Graphics.
I'm creating animated GIFs and I'd ...
- 6,049