I am developing an iPhone application in which I want set the shadow for the path that I am drawing on UIView's context.
Following is the code snippet:
CGSize shadowSize = CGSizeMake(-4, -4);
CGContextSetShadowWithColor(drawContext, shadowSize, blurRadius,
shadowColor.CGColor);
//Stroke the bezier path
Since I am drawing an UIImage in the same context of UIView, I need to flip the context. All the drawing is fine except that shadow is shown in the bottom and right-side (my expectation was top and right sides).
When I tried this drawing in a context that I created (not the UIView context and hence not flipped), the shadow is appeared properly.
What is the problem here? How do I solve this?
From Apple docs (Drawing and Printing Guide for iOS):
"Flipping the CTM to align an object with the default coordinate system of UIKit does not affect the object’s shadow, and so a shadow does not correctly track its object. To get it to track correctly, you must modify the offset values appropriately for the current coordinate system."
Related
I've used the CGContext based routine to fill a rectangle, but this time I actually want to fill all of a rectangle EXCEPT one part of it. I know this is possible in other drawing systems for other platofrm but can it be done with core graphics on iOS?
Both borderWidth and cornerRadius are animatable properties. So you could just animate them directly (using CABasicAnimation). In that rendering, you'd go from no border and no corners to having a border and corners in an animated way.
If you want to animate the rectangular tracing of the border, you'd need to use a CAShapeLayer (because the end of its path is animatable) and provide the illusion that way.
I have an image view that starts out cropping it's image with clipsToBounds and content mode set as "scale aspect fill", and I want it to "enlarge" the image to the whole image. If clipsToBounds=NO was an animatable property, that would be exactly what I want, which it does not seem to be. Is there a way to animate that?
If not, another way would be resizing the view so it is the same width-height ratio as the image's size, while keeping it no smaller than the image view was to begin with (i.e. minimal increate to height or width, no decrease to either). I'm not sure the best approach to doing this, considering the image could be much bigger or smaller than the image view, and the image's width-height ratio could be just about anything (but it will usually be an iOS device camera photo).
UPDATE 1: It seems like layer.masksToBounds would work, the documentation says that it is animatable, but my code does not seem to work:
CABasicAnimation *layerAnim = [CABasicAnimation animationWithKeyPath:#"masksToBounds"];
layerAnim.fromValue = #(YES);
layerAnim.toValue = #(NO);
layerAnim.removedOnCompletion = YES;
layerAnim.duration = 1.0;
[_imageView.layer addAnimation:layerAnim forKey:#"masksToBounds"];
I am running this layer animation at the same time as a UIView block animation that is changing the frame and transform of the image view, if that matters.
UPDATE 2: I did not have this core animation in the UIView animation block, which according to the documentation, it should be. I have moved the above code into the animation block, but it is still not animating (change happens instantly). I'm beginning to think that "animatable" simply means it can be placed in an animation, not that it will actively animate over time.
So you don't want your image to grow, but you want it to be clipped at first, and then the outer pixels are exposed?
You can do that using Core Animation and a layer mask.
Here's what you do:
Set the image view's clipsToBounds to FALSE, so the image would fully display if you let it.
Create a CAShapeLayer that's the size of the whole image. Create a rectangular bezier path that's the size of the initial image. Install that bezier path's CGPath as the path of the shape layer.
Set the shape layer's fill color to an opaque color
Then install the shape layer as the mask of your image view's layer. That will cause the image to be clipped to the shape of the shape layer.
Now, if you change the path that's installed in the shape layer to a rectangle that's the full size of the image, the system will animate the change for you.
As of March 21st 2019, it seems like the masksToBounds documentation is just wrong. masksToBounds does not seem to be animatable. I have tried animating masksToBounds with CABasicAnimation and CAKeyframeAnimations and it doesn't seem to work.
I have two UIViews. My aim is to draw the smallest rectangle which contains both these UIViews. I thought to draw a rectangle using the frame which I'll get out of
CGRectUnion(view1.frame, view2.frame);
But when I move any of the two UIViews, I need to update the frame of the outlining rectangle.
I thought I could do this by :
1) Resizing the previously drawn rectangle.
(or)
2) Deleting the previously drawn rectangle and drawing a new one.
The problem is that, I don't know how to get the instance of the previously drawn rectangle. So, I don't know how to update or delete it..
Can any of you guys help?
Is there any other solution to this problem?
Perhaps you can declare the following in your .h file:
CGRect *transformingRect;
Doing so should retain the rectangle and its properties so long as whatever view controller this is in is visible and loaded. This way you can have a method that resizes the same drawn rect. You would simply call this whenever you need to resize it.
-(void)resizeRect {
transformingRect = CGRectUnion(view1.frame, view2.frame);
}
In CALayer's API, 'position' is used for setting the position of the layer.
By my own testing, setting bounds.origin does not do anything. Am I missing something?
The bounds.origin controls where the origin of the layer's coordinate system is, relative to the layer's frame in its superlayer. Changing it has two visible effects:
The position of sublayers of the layer. For example, when you scroll a UIScrollView, the scroll view doesn't change its subview's frames. It simply changes its bounds.origin. I suggest setting up a toy app with a scroll view and doing NSLog("scroll view bounds = %#", NSStringFromCGRect(scrollView.bounds)); from a timer or some other trigger to get a sense of what's happening.
The origin of the graphics context coordinate system in drawInContext:. Mostly commonly you would see this effect in a view's drawRect: method. Your CGContext inside drawRect: will have been translated by the self.bounds.origin.
You may find it helpful to read about “View Geometry and Coordinate Systems” in the View Programming Guide for iOS and “Layer Objects Define Their Own Geometry” in the Core Animation Programming Guide, although really neither of them have a good discussion of the bounds origin.
Changing the bounds rectangle changes the position and size of the content in the coordinate system of the layer itself. Changing the frame (or position) changes the position of the layer in the coordinate system of its super layer. Usually you only want to change the frame, not the bounds.
I'm working on a educational app involving complex scripts in which I paint parts of different 'letters' different colours. UILabel is out of the question, so I've drilled down into Core Text and am having a surprisingly successful go of painting glyphs in CALayers.
What I haven't managed to do is animate the size of my custom drawn text. Basically I have text on 'tiles' (CALayers) that move around the screen. The moving around is okay, but now I want to zoom in on the ones that users press.
My idea is to try to cache a 'full resolution' tile and then draw it to scale during an animation of an image bounds. So far I've tried to draw and cache and then redraw such a tile in the following way:
UIGraphicsBeginImageContext(CGSizeMake(50, 50));
CGContextRef context = UIGraphicsGetCurrentContext();
//do some drawing...
myTextImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
Then in [CALayer drawInContext:(CGContextRef)context],
I call [myTextImage drawAtPoint:CGPointZero].
When I run the app, the console shows <Error>: CGContextDrawImage: invalid context 0x0. Meanwhile I can perfectly while just continue to draw text in context in the same method even after that error is logged.
So I have two questions: (1) Why isn't this working? Should I be using CGBitmap instead?
And more important: (2) Is there a smarter way of solving the overall problem? Maybe storing my text as paths and then somehow getting CAAnimation to draw it at different scales as the bounds of the enclosing CALayer change?
Okay, this is much easier than I thought. Simply draw the text in the drawInContext: of a CALayer inside of a UIView. Then animate the view using the transform property, and the text will shrink or expand as you like.
Just pay attention to scaling so that the text doesn't get blocky. The easiest way to do that is to make sure the transform scale factors do not go above 1. In other words, make the 'default' 1:1 size of your UIView the largest size you ever want to display it.