Is there an easy way of putting a mark (like a cross for example) on the anchor point of an UIImageView? I'm trying to line up several rotating images by their anchor point, and being able to see these points would make the job a lot easier.
Many thanks.
You are asking how to visualize the anchor point within a view but it seem to me that you are asking for it so that you can help align the anchor points. I'll try and answer both questions.
Visualizing the anchor point.
Every view on iOS have an underlying layer that has an anchor point. The anchor point is in unit coordinate space of the layer (x and y goes from 0 to 1). This means that you can multiply x by the width and y by the height to get the position of the anchor point inside the layer in the coordinate space of the view/layer. You can then place a subview/sublayer there to show the location of the anchor point.
In code you could do something like this to display a small black dot where the anchor point is.
CALayer *anchorPointLayer = [CALayer layer];
anchorPointLayer.backgroundColor = [UIColor blackColor].CGColor;
anchorPointLayer.bounds = CGRectMake(0, 0, 6, 6);
anchorPointLayer.cornerRadius = 3;
CGPoint anchor = viewWithVisibleAnchorPoint.layer.anchorPoint;
CGSize size = viewWithVisibleAnchorPoint.layer.bounds.size;
anchorPointLayer.position = CGPointMake(anchor.x * size.width,
anchor.y * size.height);
[viewWithVisibleAnchorPoint.layer addSublayer:anchorPointLayer];
You can see the result in the image below for four different rotations.
Aligning layers by their anchor point
That is cool and all but it's actually easier then that to align anchor points.
The key trick is that the position and the anchorPoint is always the same point, only in two different coordinate spaces. The position is specified in the coordinate space of the super layer. The anchor point is specified in the unit coordinate space of the layer.
The nice thing about this is that views that have their position property aligned will automatically have their anchorPoint aligned. Note that the content is drawn relative to the anchor point. Below is an example of a bunch of views that all have the same y component of their position, thus they are aligned in y.
There really isn't any special code to do this. Just make sure that the position properties are aligned.
Related
Say, I have an image on an HTML page.
I apply an affine transformation to the image using CSS3 matrix function.
It looks like:
img#myimage {
transform: matrix(a, b, c, d, tx, ty);
/* use -webkit-transform, -moz-transform etc. */
}
The origin of an HTML page is the top-left corner and the y-axis is inverted.
I'm trying to put the same image in an environment (cocos2d) where the origin is the bottom-left corner and the y-axis is upright.
To get the same result in the other environment, I need to transform the origin somehow and reflect that in the resulting CGAffineTransform.
It would be great if I can get some help with the matrix math that goes here. (I'm not so good with matrices.)
The following formula would work,
for converting the position from CSS3 to Cocos2d:
(screen Size - "y" position in CSS3 - height of object)
Explanation:
To make the origin for the Cocos environment same as for the CSS3 environment we would only have to add the screen size to the cocos2d's bodies y co-ordinate.
Eg. The screen size is (100,100) and the body is a point object if you place it at (0,0) in CSS3 it would be at the top left corner. If we add the screen size to the y co-ordinates for cocos2d the object would be placed at (0,100) which is the top-left corner for cocos2d as well
To make the co-ordinates same, since the Y axis is inverted, we have to subtract the "Y" co-ordinate given in CSS3 from the Screen Size for Cocos2d. Suppose we place the same point object in the previous example at (0,10) in CSS3 we would place it at (0, 100 - 10) in cocos2d which would be the same positions on the screen
Since our body would NOT always be a point object we have to take care of its anchor point as well. If suppose the body's height is 20 and we place it at (0,10) in CSS3 then it would be placed at the top-left position and would be coming down because the Y axis is inverted
Hence we would also have to subtract the body's total height from the screen size and "y" co-ordinate to place it at the same position which would be (0, 100 - 10 - 20) putting the body at the same place in cocos2d environment
I hope I am correct and clear :)
I have a UIBezierPath and I would like to:
Move to any coordinate on the UIView
Make bigger or smaller
I am drawing the UIBezierPath based off of a list of predefined coordinates. I implemented this code:
CGAffineTransform move = CGAffineTransformMakeTranslation(0, 0);
CGAffineTransform moveAndScale = CGAffineTransformScale(move, 1.0f, 1.0f);
[shape applyTransform:moveAndScale];
I have also tried scaling and then moving the shape, it seems to make little to no difference.
Using this code:
[shape moveToPoint:CGPointMake(0, 0)];
I start drawing the shape at (0, 0), but this is what happens. I assume this is because a line is being drawn from 0, 0 to the next point in the list.
When I set the move transformation to (0, 0) this is where it draws. Here, moveToPoint is set to the first coordinate pair in the list. As you can see, it is not at 0, 0.
Finally, increasing the 1.0f moves the shape off the screen completely, no matter where the I tell the shape to move.
Can someone help me understand why the shape is not drawing at 0, 0 and why it moves off the screen when I scale it.
(As requested by the OP in a comment above)
I might be wrong on this one, but doesn't this code
CGAffineTransformMakeTranslation(0, 0);
just say that something should be moved 0 pixels along the x-axis and 0 pixels along the y-axis? (reference) It won't actually move anything to origo (0, 0), as it seems you are trying to do.
Also, it seems like you have slightly misunderstood how to properly use moveToPoint:.. Think of it as a way to move your cursor, but without actually drawing anything. It is just a way to say 'I want to start drawing at this point'. The drawing itself can be performed by other methods. If you wanted to e.g. draw a square with sides of length L, then you could do something like this..
// 'shape' is a UIBezierPath
NSInteger L = 100;
CGPoint origin = CGPointMake(50, 50);
[shape moveToPoint:origin]; // Initial point to draw from
[shape addLineToPoint:CGPointMake(origin.x+L, origin.y)]; // Draw from origin to the right
[shape addLineToPoint:CGPointMake(origin.x+L, origin.y+L)]; // Draw a vertical line
[shape addLineToPoint:CGPointMake(origin.x, origin.y+L)]; // Draw bottom line
[shape addLineToPoint:origin]; // Draw vertical line back to origin
Note that this code is not tested at all, but it should give you the idea of how to use moveToPoint: and addLineToPoint:.
You need to be careful of the order you apply the transforms in and you should think about concatenating the transforms together and applying them in one go.
The order is important as each transform affects all x,y positions in the path. So, the translation is affected by the scale. Reverse the order and the path will be scaled and then moved.
Also, the coordinate system is important, particularly if you are scaling. Ensure you draw around 0,0 and then scale and then translate. This is easiest if you normalise the points. Normalising for lat/long values means dividing latitude by 90 and longitude by 180 (this will actually give you a range -1..1). When doing this you should first scale the path, then translate it to the centre of the view, then apply your desired translation.
I'd like to display multiple small UIViews as Subviews relative to the screen estate. This should work across different screen sizes (iPad, iPhone)/portrait/landscape modes.
Each subview to display has two NSNumber objects with an unsigned int ranging from -100 (min) to 100 (max) which needs to be mapped to the correct x and y coordinates for positioning.
What's the best way to translate those values (-100...100) to use them for positioning UIViews on the screen?
How do I position them in a relative rather then an absolute way, so that the code works across screen rotation and screen sizes?
Ok, so if I understand correctly you want a -100 in the x direction to map to the left most point on the screen, 100 in the x to map to the right most point on the screen, -100 in the y direction to map to the lowest point on the screen, and 100 in the y to map to the highest point on screen (or maybe you want the y inverted from what I have so that it agrees with the screen coordinate system in which y becomes bigger the lower on the screen you get?).
And we also want to account for rotation.
As far as I understand it, asking UIScreen for its height and width:
CGFloat width = [UIScreen mainScreen].bounds.size.width;
CGFloat height = [UIScreen mainScreen].bounds.size.height;
but this does not account for rotation. The only other way I am aware of that is pretty straightforward would be to ask a UIView covering the screen for its width and height (most simply, you could make your viewcontroller's view cover the whole screen).
If you had a UIView that perfectly covered the whole screen (let's call it myView), you could try:
CGFloat width = myView.frame.size.width;
CGFloat height = myView.frame.size.height;
these should adjust for orientation by themselves (from my experience, it should definitely work if you get the height and width in viewDidAppear:animated: or anything after. also the UIView needs to either be the UIViewControllers view property or a subview of this view. if not, you'll have to implement didRotateFromInterfaceOrientation: or find some other way to tell your view about any rotations). Once we have the 'width' and 'height' of the screen, we can convert from your int's to screen position. Try something like:
(CGPoint)convertX:(NSNumber *)x andY:(NSNumber *)y intoPoint
{
pointX = ([x intValue] + 100.0)*width/200.0;
pointY = (-[y intValue] + 100.0)*height/200.0; // remove the - sign at the front of the expression for y to grow as you move down the screen
return CGPointMake(pointX, pointY);
}
to convert from -100 to 100 in x and y to their respective points on the screen.
If you're working with a range of +/-100, then you may want to use the underlying CALayers to position your views. The nice part about CALayers, is that their anchor points are mapped to a device-agnostic grid that ranges from 0.0 to +1.0 on a Cartesian plane.
I have a UIView, which I'm drawing manually in the 'drawRect'-Function.
It is basically a coordinate system, which has 'Values' on the Y-Axis and 'Time' on the 'X-Axis'.
Due to space issues, I want the Timestamps to be vertical, instead of horizontal.
For this purpose, I use:
CGContextSaveGState(ctx); //Saves the current graphic context state
CGContextRotateCTM(ctx, M_PI_2); //Rotates the context by 90° clockwise
strPos = CGContextConvertPointToUserSpace(ctx, strPos); //SHOULD convert to Usercoordinates
[str drawAtPoint:strPos withFont:fnt]; //Draws the text to the rotated CTM
CGContextRestoreGState(ctx); //Restores the CTM to the previous state.
ctx (CGContextRef), strPos (CGPoint) and str (NSString) are variables, that have been initialized properly and correctly for 'horizontal text', with a width of the text height.
While this code works flawlessly on the iPhone 3, it gives me a complete mess on the iPhone 4 (Retina), because the CGContextConvertPointToUserSpace function produces completely different results, even though the coordinate system of the iPhone is supposed to remain the same.
I also tried using CGAffineTransform, but only with the same results.
To summarize my question: How do I draw a text to a calculated position in the parent coordinate system (0, 0 being top left)?
After studying the Apple docs regarding Quartz 2D once more, I came to realize, that the rotation by Pi/2 moves all my writing off screen to the left.
I can make the writing appear in a vertical line by translating the CTM by +height.
I'll keep trying, but would still be happy to get an answer.
Edit: Thanks to lawicko's heads-up I was able to fix the problem. See Answer for details.
I would like to thank lawicko for pointing this out.
During my tests I made two mistakes...but he is of course correct. Using CGContextShowTextAtPoint is the most simple solution, since it doesn't require the rotation of the entire CTM.
Again, THANK you.
Now, for the actual answer to my question.
To draw a rotated text at position x/y, the following code works for me.
CGAffineTransform rot = CGAffineTransformMakeRotation(M_PI_2); //Creates the rotation
CGContextSelectFont(ctx, "TrebuchetMS", 10, kCGEncodingMacRoman); //Selects the font
CGContextSetTextMatrix(ctx, CGAffineTransformScale(rot, 1, -1)); //Mirrors the rotated text, so it will be displayed correctly.
CGContextShowTextAtPoint(ctx, strPos.x, strPos.y, TS, 5); //Draws the text
ctx is the CGContext, strPos the desired position in the parent coordinate system, TS a char array.
Again, thank you lawicko.
I probably would've searched forever if not for your suggestion.
Maybe this answer will help someone else, who comes across the same problem.
I already tried reading this: http://www.qcmat.com/understanding-anchorpoint-in-cocos2d/
But I got lost in the second example. (how does an anchor point of ccp(-1,-1) mean “Place the anchor 1 * myWidth to the left and 1 * myHeight under the sprite”?) Can somebody explain how anchor points work to me?
Thanks!
An anchor point is defined relative to the sprite. E.g., if the anchor point is (0,0), then it is at the left-bottom corner; if (1,1), at the right-top corner; if (0.5, 0.5), at the center.
So, an anchor point at (-1, -1), means that it lays outside of the sprite, at the coordinates that you mention in your question. This is the opposite to the right-top corner respect to the let-bottom corner (trace a diagonal from the right-top corner to the left-bottom corner, extend it beyond the latter point and take the symmetric to the right-top corner).
If you think that scaling and rotation (and other properties) are defined relative to the anchor point, then if you set the anchor point at (-1, -1) and rotate the sprite, you will see the sprite describe a circle (this is rotating plus translating).
See this link for an interactive demo what anchors are: http://sibirjak.com/osflash/projects/as3commons-ui/layers/examples/placementdemo/ Should you tell more than long narrative descriptions.