Using the information here: iPhone Landscape-Only Utility-Template Application I am able to launch, use and maintain my view as landscape only. However, I am confused about the axis.
The absolute axis behaves as expected, meaning (0,0) is the top left, (240,0) is the top center, (0,320) is the bottom left corner, etc. However, when I attempt to do calculations related to the view I am drawing on I find x,y to be oriented as if the portrait top left were the origin. So to draw something at the center-point in my view controller I need to do:
CGPoint center = CGPointMake(self.view.center.y, self.view.center.x);
I assume this due to the fact that the UIView referenced by my controllers self.view is giving it's values relative to it's enclosing frame, meaning the window which has it's axis origin on the top left in portrait mode.
Is there some simple way to account for this that I am missing?
Documentation suggests that the transform property is exactly what I am looking for, however, I experiencing further confusion here. There are 3 essential properties involved:
frame
bounds
center
If I do this in viewDidLoad:
// calculate new center point
CGFloat x = self.view.bounds.size.width / 2.0;
CGFloat y = self.view.bounds.size.height / 2.0;
CGPoint center = CGPointMake(y, x);
// set the new center point
self.view.center = center;
// Rotate the view 90 degrees counter clockwise around the new center point.
CGAffineTransform transform = self.view.transform;
transform = CGAffineTransformRotate(transform, -(M_PI / 2.0));
self.view.transform = transform;
Now according to the reference docs, if transform is not set to the identity transform self.view.frame is undefined. So I should work with bounds and center.
self.view.center is correct now, because I set it to what I wanted it to be.
self.view.bounds appears unchanged.
self.view.frame appears to be exactly what I want it to be, but as noted above, the reference claims it is invalid.
So while I can get what I believe to be the right numbers, I fear I am overlooking something critical that will become troublesome later.
Thanks.
With Quartz 2D, the coordinate system has its origin (0,0) at the lower-left corner of the graphic, not at the upper-left corner. Maybe that's what you are missing.
See: http://developer.apple.com/documentation/graphicsimaging/Conceptual/drawingwithquartz2d/dq_overview/dq_overview.html#//apple_ref/doc/uid/TP30001066-CH202-CJBBAEEC
Related
I want to ask a question about the perspective that is achieved through CATransform3D.
I know that if you have a view that is 320x480 and then apply this:
CATransform3D perspective = CATransform3DIdentity;
CGFloat zDistance = 1000;
perspective.m34 = 1.0 / -zDistance;
view.layer.sublayerTransform = perspective;
you create a perspective that makes it look like the observer is looking straight at the center of the screen and therefore the same transformation looks different, depending on where the subview that is being transformed is located on the screen. For example, tilting a view looks like this when the view is in the middle of the screen:
And it looks like this if it's in the lower left corner:
Now, my problem is that making the perspective relative to the screen only works if the view I'm transforming is a subview of another view that is 320x480px big. But what if the view I want to transform is a subview of a view that is only 100x100px? Is there a way to make the perspective relative to the whole screen if the superview isn't the size of the screen?
Thanks in advance
According to apple
"The anchorPoint property is a CGPoint that specifies a location within the bounds of a layer that corresponds with the position coordinate. The anchor point specifies how the bounds are positioned relative to the position property, as well as serving as the point that transforms are applied around."
Your perspective should not be relative to the center of the screen or even to the center of your layer by default, is that where you have your anchor point? Aside from that though, what you seem to be asking is how to make your perspective appear to be relative to a different point. The trick is that your perspective is created by multiplying by your perspective matrix. Setting m34 to a small number does nothing magic, you are multiplying by your projection matrix.
YourProjection = {1,0,0 ,0,
0,1,0 ,0,
0,0,1 ,0,
0,0,-1.0/zdistance,1};
Remember that you can combine successive transforms by multiplying them together. Just transform your layer to wherever you want, then apply your Projection matrix, then transform it back, presto, perspective from a different origin.
float x = your coordinates relative to the screen center;
float y = same thing
TranslationMatrix = {1,0,0,0,
0,1,0,0,
0,0,1,0,
x,y,0,1};
ReverseTranslationMatrix = {1,0,0,0,
0,1,0,0,
0,0,1,0,
-x,-y,0,1};
//now just multiply them all together
Final = ReverseTranslation*YourProjection*Translation;
You will need to do the matrix math yourself, hopefully you already have a generic 4x4 column major matrix class that can do multiplication for you, if not i suggest you make one. Also, if you are interested, you might consider reading. This for an explanation of how the matrix you are currently using works, or This for a different take on projection matrices.
I've got few pixels wide circle (circle is UIBezierPath based). I have to put an arc (which is basically UIView subclass with custom drawing) on the circle so the arc covers circle. I know how to calculate rotation of arc and position but something is not right. I mean I know the reason - it's beacause center property which is assigned to center of UIView, if it was center of the arc, everything would be great. But it's not.
I also know how to solve that. I have to calculate smaller radius where I will put arcs on. But how to do that. Basically it seems easy but because of the arc is in rectangular UIView it gets a bit harder. I'll show you some images so you can see the problem.
The easiest way to do this is to change the anchor point of each arc view's layer. You can read about the anchor point here if you don't already know about it.
You will need to add the QuartzCore framework to your build target and add #import <QuartzCore/QuartzCore.h>.
CGRect circleBounds = circleView.bounds;
topArcView.layer.anchorPoint = CGPointMake(.5, 0);
topArcView.layer.position = CGPointMake(CGRectGetMidX(circleBounds), 0);
bottomArcView.layer.anchorPoint = CGPointMake(.5, 1);
bottomArcView.layer.position = CGPointMake(CGRectGetMidX(circleBounds), CGRectGetMaxY(circleBounds));
leftArcView.layer.anchorPoint = CGPointMake(0, .5);
leftArcView.layer.position = CGPointMake(circleBounds.origin.x, CGRectGetMidY(circleBounds));
rightArcView.layer.anchorPoint = CGPointMake(1, .5);
rightArcView.layer.position = CGPointMake(CGRectGetMaxX(circleBounds), CGRectGetMidY(circleBounds));
Perhaps you could make the UIView subclass the same size and center point as the circle's rect. Then draw the arc in the correct location.
I find this pretty confusing. When you want to rotate a view, it's going to be rotated by it's center point. But that's not always good. So if you need to rotate by an specified origin in your view, you would have to set the anchorPoint property of the view's layer.
Now, the problem is, that this anchorPoint property takes pretty confusing values for the average-intelligent programmer ;)
They're from 0 to 1, as far as I know. Also, the coordinate system is flipped to the view's coordinate system, where I think that 0 is the smallest value in the view's coordinate system, and 1 the largest.
myView.layer.anchorPoint = CGPointMake(0.5, 0.5);
would set the anchorPoint in the middle of the view.
What can I do, if I only know:
- my view is 100 x 150 units big
- I want the anchorPoint to be at x=100 and y=20, in my view coordinate system
Any idea how to achieve that?
Sounds like you would use
myView.layer.anchorPoint = CGPointMake(1.0, 0.133);
They are just percentage values, no? 100/100 = 1 and 150/20 = 0.133.
There are methods to transfer a CGPoint from one UIView to another and from one CALayer to another. I cannot find a way to change a CGPoint from a UIView's coordinate system to a CALayer's coordinate system.
Does a layer and it's host view have the same coordinate system? Do I need to transform points between them?
Thanks,
Corey
[EDIT]
Thanks for the answer! It is hard to find information on the differences/similarities between CA on the iPhone and Mac. I am surprised I couldn't find this issue addressed directly in any Apple Documentation.
I was pursuing this answer to help with a bug I am troubleshooting, and this was so far my best guess, but I suppose I am barking up the wrong tree. If the coordinate systems are the same, then I have another issue...
The actual issue I am having can be found here on Stack Overflow:
layer hit test only returning layer when bottom half of layer is touched
The documentation for hitTest says:
/* Returns the farthest descendant of the layer containing point 'p'.
* Siblings are searched in top-to-bottom order. 'p' is in the
* coordinate system of the receiver's superlayer. */
So you need to do (something like this):
CGPoint thePoint = [touch locationInView:self];
thePoint = [self.layer convertPoint:thePoint toLayer:self.layer.superlayer];
CALayer *theLayer = [self.layer hitTest:thePoint];
In terms of Apple documentation, I found an "iPhone OS Note" in the Layer Coordinate System section of the Core Animation Programming Guide (2008-11-13).
The default root layer of a UIView instance uses a flipped coordinate system that matches the default coordinate system of a UIView instance–the origin is in the top-left and values increase down and to the right. Layers created by instantiating CALayer directly use the standard Core Animation coordinate system.
You can set the transform property of CALayers to the appropriate transform if you want to flip their coordinate system, but note that this will probably flip their drawing of the contents as well (I have not tested that, but it makes sense that this would be true). My assertion that the CALayer associated with a UIView shares the same coordinate system could in fact be entirely erroneous. It could also be that CALayers use the same coordinate system as UIViews (i.e. they're never flipped vertically), but I thought they were since CoreGraphics uses a flipped coordinate system relative to UIKit.
A simple way to test would be to add a screen-sized CALayer as the sublayer of a view's layer, then add another small CALayer as a sublayer of that. You could set it to show up at (0, 0, 320, 100) and see if it shows up on the top or the bottom of the iPhone's screen. This will tell you in which direction the Y axis goes for CoreAnimation.
- (void)viewDidLoad {
[super viewDidLoad];
CALayer *rootLayer = [CALayer layer];
rootLayer.frame = self.view.layer.bounds;
CALayer *smallLayer = [CALayer layer];
smallLayer.frame = CGRectMake(0, 0, rootLayer.bounds.size.width, 50);
smallLayer.backgroundColor = [UIColor blueColor].CGColor;
[rootLayer addSublayer:smallLayer];
[self.view.layer addSublayer:rootLayer];
}
I just performed this test myself, and it appears CALayers actually use the same coordinate system as UIViews, so my assertion that CALayer's flip the Y axis is definitely wrong. However, if you do drawing with CoreGraphics directly, be aware that CoreGraphics does use a flipped Y axis (though when drawing in a UIView subclass or, I assume, a CALayer delegate, the CoreGraphics context has already been flipped to match the UIView's (or CALayer's) coordinate system).
So the short answer, if you made it this far, is the coordinate system for CALayer should match the coordinate system for its corresponding UIView.
From my tests I've found out that sublayers share the same coordinate system as it's parent layer and therefore if you are adding sublayer to a UIView layer then they will share the same coordinate system.
In case you still want to flip the coordinate system so that it's origin is in the upper left corner you should use this transformation that flips the y axis.
(x,y,1) = (x', y', 1) * [1 0 0],[0 -1 0],[0 heigth 1]
which translated to code is:
[your_layer setAffineTransform:CGAffineTransformMake(1,0,0,-1,0,heigth)];
I believe the coordinate system of a UIView and its associated layer should be the same. However, if you create layers yourself, the coordinate system is flipped vertically.
Methods that fixing frames and points
- (CGRect) fixRect:(CGRect)rect inRect:(CGRect)container
{
CGRect frame = rect;
frame.origin.y = container.size.height - frame.origin.y - frame.size.height;
return frame;
}
- (CGPoint) fixPoint:(CGPoint)point fromPoint:(CGSize)containerSize
{
CGPoint frame = point;
frame.y = size.height - frame.y;
return frame;
}
How can I rotate a layer using Core Animation around an arbitrary point? ( In my case a point that is not inside the layer I want to rotate )
I prefer doing this without changing the anchor point, because unless I get something wrong every time I change the anchor point it also changes the position of the layer.
I tried something like that but it didn't work:
[UIImageView beginAnimations:nil context:nil];
CATransform3D rotationTransform = CATransform3DIdentity;
rotationTransform = CATransform3DTranslate(rotationTransform, 0.0, -100.0, 0.0);
rotationTransform = CATransform3DRotate(rotationTransform, DegreesToRadians(180),
0.0, 0.0, 1.0);
rotationTransform = CATransform3DTranslate(rotationTransform, 0.0, 100.0, 0.0)
shape1.layer.transform = rotationTransform;
[UIImageView commitAnimations];
It looks like the rotation axis is moving during the rotate.
Your solution is fine but the 'expected way' is to use the anchor point.
It is moving around when you set the anchor point because the position is attached to the anchor point, i.e. setting the position sets where the anchorPoint is in the superlayer's coord system.
Probably not worth changing since you have something working, but just something to add to the grey matter for next time.
Good luck!
You can do this by appending multiple transformations:
translate the layer by (-rotCenterX, rotCenterY)
rotate the layer
translate the layer by (rotCenterX, rotCenterY)
Your initial solution is not fine as the translation is animated just like the rotation is. So the "custom-center" of your rotation is moving during the rotation. What you actually want is a translation without animation and the rotation with the animation based on that non-animated translation.
Thing is, I currently have the exact same problem and couldnt come up with a solution yet. I am looking at CATransaction at the moment, hoping that could be the key...
I finaly did it by creating a new bigger layer with it's center at my rotation axis and setting the layer i want to rotate as it's sub layer.
Then I rotate the bigger layer instead of the sub layer