I have a requirement to draw a line on a UIView in IOS with OpenGL ES. But the line that is drawn could be able to move anywhere on the view when it is touched and dragged. Simply the user can re-position the line on the screen. I have no idea how this can be implemented. The line will be drawn with OpenGL ES.
I request all your helps and suggestions regarding this.
The solution is to use a second transparent view positioned over the OpenGL view, which acts as a proxy to your line.
Create a clear view (or a view with 0.0001 opacity) and add gesture recognizers to it. Initially place that view (say sized to 44 x 320), and centered over your line (I'm assuming its horizontal). When the user drags the clear view around, post the new position you want your line to appear in within the OpenGL view then tell it to refresh.
I seem to recall (but am unsure) if you can use gesture recognizers with completely clear views - you may need to make the view slightly opaque (but no visibly so) to get touches, but again just not sure.
Related
I'm trying add a crosshair in the middle of a GMSMapView. The crosshair will not move with the map as the user pans it. It will move with the camera.
I looked at the google maps guide but it doesn't seem to talk about the kind of overlays I'm interested in. What it says is just adding overlays and shapes that moves with the map.
Therefore, I tried to come up with something on my own. I tried to add an UIImageView on top of the map view he storyboard. (Note that both the image view and the map view is in the storyboard and they are both direct subviews of the view that the VC controls)
When I run the app, I did not see the crosshair anywhere on the map. I looked at the UI hierarchy and saw this:
The little view is the image view with the crosshair, and as you can see there are 3 more views in front of it. I think this is why the crosshair did not show. The three views are, from right to left: GMSVectorMapView, GMSUISettingsPaddingView and GMSUISettingsView.
I have not idea how to bring the image view to front. I tried bring it to front by calling bringSubview(toFront:). I tried to call this in both viewDidLoad and viewDidAppear but it did nothing in both times.
How can I make such an overlay work?
You can use zPosition to achieve this
YourView.layer.zPosition = 1
by doing this you will put your view's layer to the frontmost position, but not the view itself. So position of the view won't change.
self.view.bringSubview(toFront: YourView)
Should also work, it's probably juat a timing problem.
Here's the scenario I am trying to implement:
I already have a view that can let user draw doodles by touching inside the view directly (like a doodle canvas). This view implements touchesBegan, touchMoved, and touchEnded handlers to draw lines from touch event parameters.
Now instead of that, I want user to be able to drag and move another UIView on this canvas view and can still draw lines just like they touch directly. For example, user can drag a pen image view on the canvas view to draw pen-style lines.
In this case, how can I transfer the movement of this pen image view to the canvas so it recognize it? One more question: if I want this canvas view to only recognize movements of drag other views rather than touching directly, what I should do?
(Sorry that this question is little too general, just want to get some pointer of it)... Thanks!
A better way to look at the problem is
How can I transfer movement on the canvas into the location of a pen
image view?
That's easy. You already have all the code that keeps track of movement in the canvas (touchesBegan, touchesMoved, touchesEnded), so all you need to do is change to center property of the pen view to track the movement in the canvas. (Obviously, you'll need to apply small X and Y offsets to put the center of the pen view at the correct location).
The only non-obvious detail that you need to be aware of is that the pen view must have userInteractionEnabled set to NO. That way, the pen view won't interfere with touches reaching the canvas view.
Note that UIImageView has user interaction disabled by default, so you don't need to do anything if the pen view is a UIImageView. However, if you're using a generic UIView to display the pen, then you need to disable user interaction in storyboard under the Attributes inspector or disable it in code, e.g. in viewDidLoad.
I want to draw an animation over MKMapView. I want it to be something like a compass arrow, that follows (rotates) user's taps / swipes .
So the arrow goes from the center of the screen and is of a fixed length. I don't need the line to be coordinate-specific, but I need to keep the map interactions intact (i.e. still being able to pinch-zoom on the map).
I tried to do that via MKPolyline (creating and then destroying a line), but that does not work (and from the way I had to do that I feel like it won't work). I wonder what would be the best way to handle that? Quartz?
I would accept just an explanation (which kind of view overlay over what, which classes to use), no code is necessary (but if you have a working example that's so much better ))
I draw views like a map ruler not as subview from MkMapView. I put kMapView and my ruler view into a container view. This works for views which positions are fixed on screen, like on center of screen, and are not related to a geographical position.
I have a UIScrollView over an image at the bottom of my app that acts as a dock with icons that can be scrolled through horizontally. Instead of the harsh edges of the UIScrollView, I would like the icons to fade out for a more aesthetically pleasing look. Being new to iOS development, I don't know if either of these would be valid options:
Create a faded image to use as an overlay on the scrollview so the
icons only appear through the visible portion.
Actually change the
alpha of the images based on their distance from the center (or from
each edge).
I suspect the first idea would be the most simple, but I'd like to throw this out there for any other ideas.
Note: I did see this tutorial, however that technique assumes that the background is a solid color. If I were to do it programatically, I would probably need to fade the individual images.
You can definitely implement something along the lines of #2. It'd be something similar to what the tutorial describes. The alpha transition however won't be as smooth as using the gradient layer mentioned in the tutorial or using an image since the entire icon would have the same alpha. How much discernible the difference is depends on the size of your icons. Smaller icons, very few will be able to tell the difference. Larger icons the difference would be quite clear.
You'd have to implement the
(void)scrollViewDidScroll:(UIScrollView *)scrollView
method in your scroll view's delegate class. This method will get called every time the scroll view changes the location of its content. In this method you can call its subviews and adjust their alphas as required. To optimize it a bit instead of calling the alpha adjustments on all the elements you can just update the subviews which are still partially/completely visible.
EDIT: to figure out which views to adjust you'll use the contentOffset property of the scrollView that gets passed as a parameter in the above method.
I have some view controller, that uses my own view class and XIB interface, so the view initializes from coder. In that view controller, when I move the slider, it redraws rectangle, in initial state rectangle is on full screen and when I move the slider to the left, the size of rect become smaller proportionally (from full screen to 10x14 continuously with 4 pixel intervals).
The "slider did change a value" calls some method, that sets new rectangle size end sends "setNeedsDisplay" method. And if I change to "setNeedsDisplayInRect:" method, it not updates all what I need on screen, there is some artifacts. But with debugging it updates all like I want. Tried to send deferent rectangles to update, like:
redrawRect=CGRectUnion(oldRect, newRect);
[cView setNeedsDisplayInRect:redrawRect];
and some others, same story. My question is, which rectangle I need to send in "setNeedsDisplayInRect:" ?
And the second question, how can I accelerate/optimize all that story for smoother animation and less cost?
Already solved the problem 1. The "setNeedsDisplayInRect:" method uses points, and not pixels like I thought.