Can anyone tell me about how to color with pattern(Butterfly) like follwing link a link.
In addition to reading the entirety of the CGLayer reference you posted in your original question I strongly advise you to watch the 'Optimizing 2D Graphics and Animation Performance' session from the 2012 WWDC.
As you progress I think you'll find that it isn't particularly difficult to draw content to the screen using the likes of Quartz 2D and Core Animation but the real challenge will be doing so in a way that achieves an acceptable level of performance.
In the session they optimise a drawing app similar to the one you want to create. The fundamental principals they used to optimize their drawing app were:
Only ever update as little of the screen as you need to
Every so often create a flat composite image of what the user has drawn and re-use this image in proceeding drawing operations. This prevents having to draw everything the user has drawn to the canvas individually, making the application much more performant.
In addition to this they cover a collection of tricks to squeeze out every drop of performance.
I apologise that I have no code examples for you (I usually like my answers to include some) but your question was very broad. I suggest you watch the video I have suggested, continue your research and attempt to begin implementing the application yourself. Once you run into more specific problems you can return here for answers in the event you can't find them elsewhere.
Good luck!
Related
I need access to the coordinates of individual strokes of a PKDrawing in PencilKit. Is there any way I can get access to that? Currently, my only idea is to try and decode the opaque data representation we get from PKDrawing.
As Ben has said, there doesn't seem to be any way to access stroke-level data in PencilKit at this time. This seems like a pretty rudimentary feature so hopefully Apple will add it next WWDC. Fingers crossed.
LetsBuildThatApp's YouTube tutorial is a good starting point if you just want basic drawing capabilities and are not too concerned about drawing quality or latency. I ran into issues when I tried to add the ability to vary the stroke width with pen pressure. I was never able to get it to transition smoothly between stroke segments of different widths - it always 'jumped' jarringly from one width to the next. Maybe there's a way to fix that, but I wasn't able to.
I suspect that currently, the only way to draw low-latency high-quality images with Apple Pencil is to write a drawing engine from scratch in Metal or OpenCL. It's strange it has taken Apple so long since the release of Apple Pencil to get a comprehensive drawing framework out. Fingers crossed that changes at WWDC 2020.
Edit: Apple announced substantial updates to PencilKit at WWDC20, including access to stroke data and functions to programatically draw strokes.
I was was looking for the same thing and from this comment https://stackoverflow.com/a/57565661/8891611 and my own searching of the documentation, it seems what you're asking for doesn't exist. If you do discover a way to decode the opaque data please update this thread on how so.
If you aren't necessarily set on PencilKit, you could manually code your drawing functions which is easier than it sounds. In this tutorial: https://youtu.be/E2NTCmEsdSE?t=504 I have timestamped where he shows that he has access to all the points on the lines he is creating.
And another potential solution could be to use both, by have a mapping between your PencilKit drawing and the points found from the technique in this tutorial.
For the strokes, you can access the property .renderBounds that gives you the dimensions of the rectangle where the stroke is into.
ask a general question. There are few sprite resources and they are hardly liked by me. I would like to learn from the absolute scratch, such as how do I create a sprite from my idea.
Can I ask do I create it this way or what's the standard process?
1. draw it on white paper
2. scan it into a .png jpg etc
3. render it in photoshop
Thanks.
It's not quite right for Stack Overflow indeed, but I have a few suggestions anyway.
If you want to hand draw your art there are a few approaches. I started drawing the resources I needed on paper and scanning them, but this raises a couple of problems.
The first problem is that it can be hard to remove the white background properly leaving nasty bitty edges. This can be solved with time, practice and patience, and as far as I know there is no good way around this.
When using paper, it can be very hard to get clean areas of solid color. Pencils and the like leave and extremely distinctive paper texture, but approaches that give more solid colors using inks tend to go very blotchy.
The other problem is that if you want to animate these, or indeed reuse part of one sprite in another, you're left drawing bits of sprites - this lead me on to my currently favored methodology.
My recommendation would be to use ink onto acetate. You'll need to do some research into the best inks to use, but it means you can build the sprites in layers, much like animators used to do for film back in the day. You still have to solve the white background problem after scanning though, and if you pick the wrong ink it can be very easy to smudge your drawings - not ideal.
The other, more expensive alternative is to use a graphics tablet, and cut out the paper/acetate stage all together. This solves the white background problem, but some people find drawing with tablets oddly difficult - myself included.
Adobe software wise - I would personally use Illustrator while working with a graphics tablet, Photoshop for making adjustments to the resulting images, and Fireworks for building UI interface elements.
Hope this helps!
This is not really a coding question. As far as I know stackoverflow is only for technical problems. That said, I would recommend Illustrator to get started. There are some great tutorials out there. :)
I'm a noob to this forum, but wanted to give it a try.
I'm currently learning Objective-C and Cocoa; trying to build my first iPhone app.
One thing I'm working on is allowing the user to cut his/her face from an image they have taken and paste it into another image. (The idea is cut from one image and paste into another image with a spot for a face to go.)
How can this be done? I am thinking I would allow the user to just touch and drag over their face, in the shape of a rectangle, and then allow them to copy.
Thanks for the help.
Ok, nevertheless your bit arrogant style of asking, here are some guidelines about how to start: generic obj-c/iOS development (start from hello world); UIImage class; camera API; image processing algorithms, face detection algorithms. Go on gradually and do not wish to resolve all problems at once. Write first an application that simple loads an arbitrary photo and shows it to the user. Then modify it that you can crop a specified rectangular area from the image and save it into the new file. Then write an app that switches on the camera that you can take an image and save it to the disk. Then unite what you wrote that you save only a cropped area of the captured image.
When you arrive to this point, you will know much more about software development image handling. AFTER THIS you can start looking for image processing algorithms. Start also here with something simple like a trivial blur filter or similar implemented by you. If you know already a bit of image processing, search for face detection algorithms on the net. It is even possible that you will find some ready framework that includes also these features, or at least you will understand the concepts. You can even come back here to stack overflow and ask for suggestions about a good face detection algorithms, however we still prefer if you have chosen already one and have some concrete issue with it.
I'm currently trying to write an app, that would be able to show the effects of glas, as seen through the iPhone Camera.
I'm not talking about simple, uniform glas but glass like this:
Now I already broke this into two problems:
1) Apply some Image Filter to the 2D-frames presented by the iPhone Camera. This has been done and seems possible, e.g. in the app: faceman
2) I need to get the individual lighting properties of a sheet of glas that my client supplies me with. Now basicly, there must be a way to read the information about how the glas distorts ands skews the image. I think It might be somehow possible to make a high-res picture of the plate of glasplate, laid on a checkerboard-image and somehow analyze this.
Now, I'm mostly searching for literature, weblinks on how you guys think I could start at 2. It doesn't need to be exact, in the end I just need something that looks approximately like the sheet of glass I want to show. And I'm don't even know where to search, Physics, Image Filtering or Comupational Photography books.
EDIT: I'm currently thinking, that one easy solution could be bump-mapping the texture on top of the camera-feed, I asked another question on this here.
You need to start with OpenGL. You want to effectively have a texture - similar to the one you've got above - displace the texture below it (the live camera view) to give the impression of depth and distortion. This is a 'non-trivial' problem, in that whilst it's a fairly standard problem in its field if you're coming from a background with no graphics or OpenGL experience you can expect a very steep learning curve.
So in short, the only way you can achieve this realistically on iOS is to use OpenGL, and that should be your starting point. Apple have a few guides on the matter, but you'll be better off looking elsewhere. There are some useful books such as the OpenGL ES 2.0 Programming Guide that can get you off on the right track, but where you start would depend on how comfortable you are with 3D graphics and C.
Just wanted to add that I solved this old answer using the refraction example in the Khronos OpenGl ES SDK.
Wrote a blog-entry with pictures about it :
simulating windows with refraction
I'm creating an interactive e-book for the iPad. This book will contain multiple pages that will consist of a lot of animations (frame and motion animations), transitions,... I was wondering what my development options are, should I use OpenGL, Quartz,...?
I've use UIImageView.animationImages before and found that it had really bad performance. What's the best way to draw frame based animations?
Does anybody have some good pointers to resources on this?
thanks in advance,
Thomas
I guess that depends a bit on what you'll be drawing. If you have a need for 3D, then OpenGL is the way to go, but it doesn't sound like it. I have a feeling Quartz2D is going to be just fine for your 2D drawing needs. I've done drawing with both and they have a very similar API. I think the downside of using all the raw power of OpenGL is that you have then signed up for doing most of the work yourself. I don't recommend attempting to using Core Animation high level APIs to manipulate OpenGL views.
If you do use Quartz2D and "normal" UIViews instead of OpenGL/EAGLView, then you can take advantage the many pre-canned animations Apple already build with Core Animation. This include the card flip left/right, resizing, moving (x/y translation), rotation and the ever popular e-book page curl.
The best example of iBook like custom page curl functionality I could find is this example code from High Caffeine Content. However, you don't have to bring that much math to the table if you just want to use the out of the box Core Animation stuff. The bad performance you may have encountered could have been due to anything, including older/slower hardware. They have revved the graphics chips on the new devices.