I want to be able to select some area from this image, and change the color of the selected area.
To do this, I thought of using CALayer and UIBezierPath.
I've cleared the colored area from the image, then I took each area point and drew a UIBezierPath beneath the image.
I have 3 CALayers for each area, each CALayer has a UIBezierPath with predefined points.
When the user clicks on a layer, it will show the selected layer without filling the UIBezierPath, just to have a border around the UIBezierPath, the result look like this:
I added a UIView over the image with Opacity = 0.6f and
redrew all the CALayers on it.
All the layers are hidden in the new UIView
Every thing is working great, the next step is to merge the selected areas:
I took the points from the first area and added it to the points of
the second area
I created a new UIBezierPath with the new points
My problem is that the result is wrong:
How to merge a UIBezierPath with a correct points order?
Is there a better way to accomplish something like this without
using UIBezierPath?
from looking at the image above, the path is wrong because the sequence of points is not followed which pretty much screws up your path. I don't think a Bezier Path is the right tool to do this in the first place as you have rectangular or point to point connections. So you more have a Poligon than a Bezier Path object. However UIKit seems to bundle all this into a UIBezierPath object (non optimal naming if you ask me).
The tricky thing here is to find out where the two shapes really touch each other and to add the points in the sequence as before but then tear up the vertical lines in the middle and connect the path to the other structure.
Another alternative could be to use a bitmap and simply union the bitmaps and create a new shape. It largely depends on how your base data is represented and managed. You could also simply keep two shapes and just join them in a meta object to draw them concurrently.
Related
I am using a CAShapeLayer to display a path that is updated as the user traces his/her finger on the screen. I'd like to transform this path to a rectangle that just encloses the path. I can compute the rectangle just fine; the tricky part is animating the transformation.
The docs say this about animating the path property of CAShapeLayer:
If the two paths have a different number of control points or segments the results are undefined.
So how do I go about adding more control points to the rectangular CGPath? Or is there a better way to achieve this animation? Thanks. =)
I think you have to manually construct a series of lines in the form of a rectangle. Iterate over the elements in the path, compute where on the bounding rectangle you want that point to transform to, and add that segment to the new rectangular path. You may have to use the same kind of element (e.g. cubic or quadratic Bézier curve that happens to form a straight line) so that the number of control points matches.
After the animation completes, you can reset the path to a pure rectangle if you want.
I am making an app that allows the user to draw on the screen with his finger in different colors. The drawings are drawn with UIBezierPaths but I need an eraser. I did have an eraser that was just a path with the background image as the color but this method causes memory issues. I would like to delete the points from any path that is drawn on when eraser is selected.
Unfortunately UIBezierPath doesn't have a subtraction function so I want to make my own. So if eraser is selected, it will look at all the points that should be erased and see if any of the existing paths contain those points, then subdivide the path leaving a blank spot. But it should be able to see how many points in a row to delete not do it one at a time. In theory it makes sense but I'm having trouble getting started on the implementation.
Anyone have any guidance to set me on the right 'path'?
Upon first glance, it appears that you could do hit detection on a UIBezierPath by simply using containsPoint:. That works fine if you want to determine whether the point is contained in the fill of a UIBezierPath, but it does not work for determining whether only the stroke of the UIBezierPath intersects the point. Detecting whether or not a given point is in the stroke of a UIBezierPath can be done as described in the "Doing Hit-Detection on a Path" section at the bottom of this page. Actually, the code sample they give could be used either way. The basic idea is that you have to use the Core Graphics method CGContextPathContainsPoint.
Depending on how large the eraser brush is, you will probably want to check several different points on the edge of the brush circle to see if they intersect the curve, and you'll probably have to iterate through your UIBezierPaths until you get a hit. You should be able to optimize the search by using the bounds of the UIBezierPath.
After you detect that a point intersects a UIBezierPath, you must do the actual split of the path. There appears to be a good outline of the algorithm in this post. The main idea there is to use De Casteljau's algorithm to perform the subdivision of the curve. There are various implementations of the algorithm that you should be able to find with a quick search, including some in C++.
I've created a canvas within which I display an image that is clipped when it goes over the edges. I can do this fine with a square shaped frame, however the frame I want to use is the one below. Is there any way I can clip the image inside the frame without having to add a non transparent square border around the image, i.e. just using the black line that I've already drawn? (on iPad)
You'll need to use Core Graphics and Quartz to handle this sort of clipping/graphics manipulation.
http://developer.apple.com/library/ios/#documentation/GraphicsImaging/Conceptual/drawingwithquartz2d/Introduction/Introduction.html#//apple_ref/doc/uid/TP30001066
If you're using UIBezierPath, you may be able to achieve the clipping you're after using the following process
http://developer.apple.com/library/ios/#documentation/GraphicsImaging/Conceptual/drawingwithquartz2d/dq_paths/dq_paths.html#//apple_ref/doc/uid/TP30001066-CH211-TPXREF101
Convert your UIBezierPath to a CGPath
Get your image into a CGContext
Add your CGPath to the context via CGContextAddPath
Clip your context using CGContextClip
Alternatively, if you don't want to be messing with paths (and depending on whether this technique is suitable for your situation, your description of the issue makes it hard to tell), it might be worth using image masking to achieve the effect you're after. See the first link and look under "Bitmap Images and Image Masks".
I have been looking for the solution on the web for a long time. Most tutorials are fairly simple about adding shadow to a UIView. I also noticed that if we add a shadow to an UIImageView. The shadow shape could perfectly fit the shape of the content image if the image itself has alpha channel in it. Say for example, if the image is an animal with transparent background, the shadow shape is also the same as that animal (not a rectangle shadow as same as UIImageView frame).
But these are not enough. What I need to do is to add some changes to the shadow so it may have some rotation angle and compressed (squeezed or shift) effect so that looks like the sunlight comes from a certain spot.
To demonstrate what I need, I upload 2 images below, which I captured from the Google Map App created by Apple. You can imagine the Annotation Pin is an image which has the Pin shape, so the shadow is also "pin shaped", but it is not simply "offset" with a CGSize, you can see the top of the shadow is shifted right about 35 degrees and slightly squeezed the height.
When we tap and hold and pin, the shadow is also animated away from the pin, so I believe that such shadow can be made programmably.
The best shadow tutorial I can found so far is http://nachbaur.com/blog/fun-shadow-effects-using-custom-calayer-shadowpaths But unfortunately, that cannot make this effect.
If anyone know the answer or know any better words to search for, please let me know. Thank you.
(Please note that the shape of the image is dynamic in the App, so using any tool like Photoshop to pre-render the shadow is not an option.)
In order to create dynamic effects like this, you have to use Core Graphics. It's incredibly powerful once you know how to use it. Basically you need to set a skew transform on the context, set up a shadow and draw the image. You will probably have to use transparency layers as well.
It doesn't sound like you can use CALayer shadows, since that is meant to solve a specific use-case. The approach Apple takes with the pin marks on the map is to have two separate images that are created ahead of time (e.g. in Photoshop) and they position them within the map relative to a reference point.
If you really do need to do this at run-time, it should still be possible by using either Core Graphics or ImageKit. To get a blurred shadow appearance, you can use the kCICategoryBlur CIFilter. You can then convert the image to grayscale. And to get that compressed look you just need to resize and skew the image.
Once you have two separate images, you can either take the CGImageRef for the shadow image and can set that as the content of another sublayer, or you can add it as a separate view.
If you know what all the shapes are, you could just render a shadow image in Photoshop or something.
i want to show a grapph/bar chart in iphone how do i do this without custom API;s
You may want to investigate the Core Plot project [code.google.com]. Core Plot was the subject of this year's scientific coding project at WWDC and is pretty useable for some cases already. From its inception, Core Plot was intended for both OS X and iPhone uses. The source distribution (there hasn't been a binary release yet) comes with both OS X and iPhone example applications and there's info on the project wiki for using it as a library in an iPhone app. Here's an example of it's current plotting capabilities.
(source: googlecode.com)
Write your own. It's not easy, I'm in the process of doing the same thing right now. Here's how I'm doing it:
First, ignore any desire you may have to try using a UIScrollView if you want to allow zooming. It's totally not worth it.
Second, create something like a GraphElement protocol. I have a hierarchy that looks something like this:
GraphElement
GraphPathElement
GraphDataElement
GraphDataSupplierElement
GraphElement contains the basic necessary methods for a graph element, including how to draw, a maximum width (for zooming in), whether a point is within that element (for touches) and the standard touchBegan, touchMoved, and touchEnded functions.
GraphPathElement contains a CGPath, a line color and width, a fill color and a drawing mode. Whenever it's prompted to draw, it simply adds the path to the context, sets the colors and line width, and draws the path with the given drawing mode.
GraphDataElement, as a subclass of GraphPathElement, takes in a set of data in x-y coordinates, a graph type (bar or line), a frame, and a bounds. The frame is the actual size of the created output CGPath. The bounds is the size of the data in input coordinates. Essentially, it lets you scale the data to the screen size.
It creates a graph by first calculating an affine transform to transform the bounds to the frame, then it loops through each point and adds it as data to a path, applying that transform to the point before adding it. How it adds data depends on the type.
If it's a bar graph, it creates a rectangle of width 0, origin at (x,frame.size.height-y), and height=y. Then it "insets" the graph by -3 pixels horizontally, and adds that to the path.
If it's a line graph, it's much simpler. It just moves to the first point, then for each other point, it adds a line to that point, adds a circle in a rect around that point, then moves back to that point to go on to the next point.
GraphDataSupplierElement is the interface to my database that actually contains all the data. It determines what kind of graph it should be, formats the data into the required type for GraphDataElement, and passes it on, with the color to use for that particular graph.
For me, the x-axis is time, and is represented as NSTimeIntervals. The GraphDataSupplierElement contains a minDate and maxDate so that a GraphDateElement can draw the x-axis labels as required.
Once all this is done, you need to create the actual graph. You can go about it several ways. One option is to keep all the elements in an NSArray and whenever drawRect: is called, loop through each element and draw it. Another option is to create a CALayer for each element, and use the GraphPathElement as the CALayer's delegate. Or you could make GraphPathElement extend from CALayer directly. It's up to you on this one. I haven't gotten as far as trying CALayers yet, I'm still stuck in the simple NSArray stage. I may move to CALayers at some point, once I'm satisfied with how everything looks.
So, all in all, the idea is that you create the graph as one or many CGPaths beforehand, and just draw that when you need to draw the graph, rather than trying to actually parse data whenever you get a drawRect: call.
Scaling can be done by keeping the source data in your GraphDataElement, and just change the frame so that the scaling of the bounds to the frame creates a CGPath wider than the screen, or whatever your needs are. I basically re-implemented my own pinch-zoom for my Graph UIView subclass that only scales horizontally, by changing its transform, then on completion, get the current frame, reset the transform to identity, set the frame to the saved value, and set the frame of all of the GraphElements to the new frame as well, to make them scale. Then just call [self setNeedsDisplay] to draw.
Anyway, that's a bit ramble-ish, but it's an outline of how I made it happen. If you have more specific questions, feel free to comment.