I am using CIContext method - (void)drawImage:(CIImage *)im inRect:(CGRect)dest fromRect:(CGRect)src to draw my image to screen. But I need to implement zoom-in/zoom-out method. How could I achieve it? I think zoom-in could be achieved increasing dest rect, because apple docs says:
The image is scaled to fill the destination rectangle.
But what about zoom-out? Because if dest rectangle is scaled down, then image is drawn in it's actual size, but only part of image is visible then (part that fits in dest rectangle).
What could you suggest?
You may try using this for image resizing (zooming). Hope this helps you.
Take a look at this little toy app I made
It's to demonstrate the NSImage version of your CIContext method:
- (void)drawInRect:(NSRect)dstRect
fromRect:(NSRect)srcRect
operation:(NSCompositingOperation)op
fraction:(CGFloat)delta
I did this to find out exactly how the rects relate to each other. It's interactive, you can play with the sliders and move/zoom the images. Not a solution, but it might help you work things out.
You can use CIFilter to resize your CIImage before drawing. Quartz Composer comes with a good example of using this filter. Just look up the description of the Image Resize filter in QC.
EDIT:
Another good filter for scaling is CILanczosScaleTransform. There is a snippet demonstrating basic usage.
Related
I am working on drag and drop activity for iPad. I have a rectangle PNG image (see the image named as obj2). When I drag obj1 only on the black portion of the rectangle then it should react.
if (CGRectIntersectsRect(obj1.frame, obj2.frame))
{
NSLog(#" hit test done!! ");
}
Right now, this piece of code takes hit test even on the transparent area. How to prevent that to happen?
For something as simple as your specific example (triangle and circle), the link that David Rönnqvist gives is very useful. You should definitely look at it to see some available tools. But for the general case, the best bet is clipping, drawing, and searching.
For some background, see Clipping a CGRRect to a CGPath.
First, create an alpha-only bitmap image. This is explained in the above link.
Next, clip your context to one of your images using CGContextClipToMask().
Now, draw your other image onto the context.
Finally, search the bitmap data for any colored pixels (see the above link for example code).
If any of the pixels colored, then there is some overlap.
Another, similar approach (which might actually be faster), is to draw each image into its own alpha-only CGBitmapContext. Then walk the pixels in each context and see if they ever are both >128 at the same time.
I have two CIImages. I'm trying to apply a CGAffineTransformation to the top image, and then pass it through along with the background image to the CIFilter for blending, but my resulting image seems to show the top image moving around (I just want it rotated on the spot).
I'm also having the same problem when scaling (the position of the top image seems to change).
What am I missing?
So after lots of digging, turns out my problem was due to the rotation point. This question/answer helped a lot.
CGContext rotation
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.
hi
i have a background pattern image (vertical lines) like:
llllllllllllllllllllllllll
the line is a pattern image:
bgimg.backgroundColor = [UIColor colorWithPatternImage:[UIImage imageNamed:#"pd_line2.png"]];
my problem:
i would like to reframe the bgimg - it should repeat the line on x-axis: but stretch the line on y-axis.
next problem: the pattern image also uses an alpha channel.
is this possible?
can someone please give me a hint?
thanks in advance
Well you can certainly scale the image in various ways via GCContext functions, but perhaps the easier way would be making your view transparent (clearColor background) and adding an extra UIImageView (with pd_line2.png in it) underneath.
UIImageView's built-in stretching options may be enough to achieve what you need without any coding.
I know similar questions have been asked before, so don't get snarky and link to previous answers. The reason I am repeating this is that none of the answers have worked.
I have a UIWebView, and I want to draw a pretty drop-shadow behind it. I have tried subclassing and using some CoreGraphics goodness in drawRect:, but to no avail. Can anyone point me in the right direction? Thanks.
You could place a UIImageView under the UIScrollView with a slight offset, and give the image view a shadowy-looking image.
In this case, it would be convenient to use the stretchableImageWithLeftCapWidth:topCapHeight: method of UIImage to get a shadow image that can have nicely blurred edges and corners without distorting if you alter its size.
I think the usual quartz shadows are hard to apply to a UIWebView since you don't really have access to the raw drawing code, which would be the best place to plug that in.
Addendum Here's a sample drop shadow image:
. It has 4 pixel cap size all around, for use with the above stretchableImage method, and an alpha of 80% (so it's 20% transparent in the middle, tapering out at the edges). Feel free to use it. They're easy to make with a selection + feathering in your favorite graphics app.