I have a UIImageView displaing an image. This view's layer is masked with CAShapeLayer in order to create circular "hole" in the image. To create the hole I use UIBezierPath with .usesEvenOddFillRule = true.
It works fine when static. But I need that hole to move with user finger. To do that I create new UIBezierPath with even-odd rule each time user moves their finger. On smaller phones with smaller images it looks OK but on iPhone 6 Plus it is choppy.
Any ideas on how to make it smooth are very wellcome. I cannot just move the frame of masking CAShapeLayer - it would move the hole bot also hide some edges of the image. So the only way is to change its .path each time user moves finger and that is slow.
EDIT: matt's answer would work in some scenarios but not in my case: I am not displaying the whole image only a part of it defined by UIBezierPath. This part is most often oval (but can be rectangular or rounded rectangle) and it has "hole" cut in it. While the hole is mowing with users finger the displayed part/shape of the image does not change - it is static.
The ineficient solution that was in place so far wa:
Create UIBezierPath with boundary of displayed part of the image
Set 'even off fill rule' on it
Add UIBezierPath of the hole to it
Set it as path of CAShapeLayer with some opaque fill color
Use that CAShapeLayer as mask of the UIImageView
This procedure was repeated each time a user moved their finger. I cannot simply move the whole mask layer as that would also change the part of the image being displayed. I what it to stay static and move only the hole in it.
it would move the hole bot also hide some edges of the image
Well, I don't agree. Moving the mask is exactly the way to do this. I don't see why you think there's a problem with that. Perhaps the issue is merely that you have not made the mask layer big enough. It does not have to be the same size as the layer it is masking. In this case, it needs to be about 9 times the size of the masked layer (3 horizontal and 3 vertical), so that it will continue to cover the masked the layer no matter how far in any direction the user slides it.
Related
I'm working on a drawing app, where user should be able to both fill locked areas and simply draw lines on finger moves.
Locked areas are provided as SVGs (paths), so I'm using SVGKit library to render them on the screen (as CAShapeLayers within a view). Then basically use fillColor on proper layer to fill it on touch.
However, for lines drawing then Core Graphics comes into play (CGContextStrokePath), and lines are always drawn below everything contained within CALayers hierarchy. So basically below filled areas.
What I'm trying to reach is a system where last applied drawing is always on top. So that applying fill overrides any lines in the area, and next drawing a line shows it above filled zone.
Seems that CGLayer's z-index is less than CALayer's one, and I need some other approach for my goal...
CAShapeLayer is designed to hold CGPath instances and render them, so I'd add a CAShapeLayer at the point in your layer-hierarchy where you want it to appear, and modify the CGPath property on that.
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 am having some difficulty understanding on how layer masking works. Right now, I have a UIView with UILabels on it. I picture two layers - one with the UIView in the back and one for the labels on top. If I mask the UIView layer, the labels will be affected by the mask too.
The UILabels are children of the parent UIView, so I can understand a parent mask affecting the children as well.
However, when I look at it in terms of layers, it doesn't seem to make sense. Why does masking the deepest layer affect those on top?
Think of layers as sheets of paper. Think of the view's layer as a big sheet of white paper. As you figured out, the labels' layers are children of the view's layers. To relate, think of the labels' layers being strips of paper glued onto the big view's layer-sheet.
Let's say you wish to mask the layer with a circle. To translate that into our little analogy, you wish to cover the big view's layer-sheet with Harry Potter's invisibility cloak, with a circle shaped hole in it.
To do that, you'd cut the invisibility cloak to the same size as that of your view's layer-sheet.
cloakLayer.frame = bigViewLayer.frame;
Then, you'd carefully cut out a circle from it.
cloakLayer.path = [UIBezierPath bezierPathWithArcCenter:CGPointMake(0, 0) radius:15.0 startAngle:0.0 endAngle:2 * M_PI clockwise:YES];
cloakLayer.fillColor = [UIColor blackColor].CGColor; // the hole
Then, you'd paste this cloak-with-a-hole onto your big view's layer-sheet, carefully aligning the edges.
bigViewLayer.mask = cloakLayer;
What's gonna go invisible? Anything on the sheet (because the cloak was cut to the sheet's dimensions) that doesn't fall into the circle you removed from the cloak. That's the mask property.
Let's talk about the masksToBounds property.
Let's say while pasting the strips of label layer-sheets onto the big view's layer-sheet, you decided to place only half of the strip on the sheet, and made the rest hang off the edge(s).
Let's say you set masksToBounds to YES. What the gods of decoupage would do now is neatly cut off the parts of your labels' strips that are not within the edges of the big view's layer-sheet. That's the masksToBounds property.
Let's talk about borders. This is simple. Just pick a sharpie of borderColor whose nib is borderWidth points wide, and carefully draw on the edges of the view's layer-sheet. That's it.
I hope you get things now and can make your own analogies for other properties of the wonderful CALayer.
As you said, the UIView is the parent, and the UILabels are the children. When it comes time to update the screen, the UIView starts with a blank canvas. It draws itself into the canvas, and then has the children draw themselves into the canvas. When the children are drawing, they are subject to constraints imposed by the parent, e.g. clipping and masking.
iOS CALayer.mask
[CALayer]
[iOS CALayer.masksToBounds]
CALayer has a mask property which is CALayer, which applies mask's alpha channel to mask parent's layer.
layer + mask = masked layer
I have an UIImageview that contains a circle (The obstacle) and then another UIImageview that contains another image (my character). When my circle hits my character the game ends.
My problem occurs when the game ends on the character touching the UIImageview box that my circle is within, rather than the circle inside the UIImageview box.
The solutions I can think of are:
Make the UIImageview rounded to fit my circle.
Somehow detect a collision between my characters pixels and the circles pixels rather than the UIImageviews.
Help and ideas would be really appreciated. I am a beginner with xcode.
Thanks!
Couple of different techniques:
1)UIView#layer.cornerRadius - Super simple to implement, just set that one property. But really bad for scrolling elements like table views.
2)UIImageView as a mask - Also easy to implement. Basically make a square image with a transparent circle in the middle and slap it on top of your view with a new UIImageView. If your circle design has some reflections or styling, this might make your life easier.
3)Custom drawing - Make a UIView subclass and override drawRect to draw your image and clip it to a circular path.
Hope that helps!
EDIT:
You can read this answers.
1)Fill an UIBezierPath with a UIImage
2)iOS: Inverse UIBezierPath (bezierPathWithOvalInRect)
3)How to mask a square image into an image with round corners in the iPhone SDK?
I'm drawing a few circles, each filled with an image. When the user pans I'd like to scale/resize the circles. So I called drawRect again and again, redrawing every GCRect until the gesture was completed - of course the animation was very choppy. In my case a UIScrollView doesn't fit the needs, because I don't want to scroll, but to scale the circles while the user is panning.
Is there any way except using OpenGL ES to implement this functionality?
Do you really need custom drawing for this? You can easily clip an image to a circle without drawRect.
Without -drawRect:
Using Core Animation you can set the corner radius of a layer. If all you want is to show an image inside a circle then you can put the image in an image view with a square frame and set the corner radius of the image views layer to half the width of the frame.
Now each time the user drags you can change the bounds and the corner radius of the image views layer. This will make it look like the circle becomes bigger/smaller.
If you require custom drawing
Maybe you are doing some custom shadows or blending that can only be done with Core Graphics. If so, you could apply a scale transform and stretch the image while the user is dragging their finger and only redraw once the finger lifts from the screen. That will be much, much cheaper and is also very easy to implement. Just create a scale transform (CGAffineTransformMakeScale(xScale, yScale);) and set it as the transform on the view with the circle (this will only work if each circle is its own view).
Note: You can still use the same trick (scaling while dragging and then redrawing) if you use the corner radius approach if you require the extra performance.