Interview with Zenny Chen: iOS developers should pay attention to Metal

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CocoaChina: How did you get involved in iOS development?

Zenny Chen: I registered CocoaChina in 2009. I felt that this forum was very professional in OS X and iOS development, so I joined it with great enthusiasm to discuss OS X and iOS development with everyone. I have previously worked on embedded device driver development and feature phone application development, so I am familiar with the underlying hardware. In November 2011, I officially entered the mobile Internet industry.

My relationship with iOS is bizarre. In 2008, I planned to make games and even wanted to start a business. But I didn’t have a clear goal. Which platform should I develop games for? I looked into Sony, Nintendo, etc. The licensing fees were quite scary, and small and micro enterprises simply couldn’t afford it. In addition, the review was quite strict, and the entry threshold was quite high. Later, I accidentally discovered the App Store. After learning a lot about it, I bought my first Mac in my life, a Mac Mini, in May 2009. I spent 4,988 yuan at the time, and then I started on the road of iOS development.

CocoaChina: You have given a lecture on Swift before. What do you think of this language? Do you need to start learning it now?

Zenny Chen: The Swift language seems to have been released in a hurry. A lot of things have changed since Beta 1. For example, the array type was type[] at the beginning, but now it is [type]. Of course, this cannot hide its advanced nature. Swift is one of the few compiled programming languages ​​I have seen that supports many dynamic features such as tuples and closures. The closure in Swift is different from Lambda in C++, Blocks in LLVM Clang C extension, and Lambda expressions in Java. Its expression is more concise and functional, very expressive! So when you use Swift, it feels like you are using a script like Python, and a functional programming language like Scheme, while also containing object-oriented features (of course, this is available in scripting languages ​​such as Python and JavaScript).

Swift is a very complex programming language, second only to C++ in complexity, and much more complex than C and Objective-C. However, because it can adopt multiple programming paradigms, the entry threshold for programmers is actually relatively low. The public lecture on Swift programming language that I will hold in mid-October will also invite some product managers, planners, and even artists who have little programming experience. And combined with the playground that comes with Xcode, learning is also vivid and interesting. And if you want to master it and know all its pitfalls, it will take a lot of time and energy, and you have to use it formally to do a few projects.

I think using Swift for development will become a general trend. As I described before, many companies are still focusing on the iOS platform, so artists often design based on the iPhone/iPad screen. If they can directly cut the image, put it in the storyboard, and then use Swift programming to see the actual running effect, then think about it, the pressure on application developers will be reduced a lot. In addition, in the past, after the artists cut the image, they had to measure the coordinates themselves and then tell the developers, which also had some additional costs in communication. If the artists can organize the basic interface themselves, it will not increase too much work pressure for them. On the contrary, it will feel more interesting and more fulfilling.

Therefore, I think the future scenario of iOS development will be that iOS professional developers can combine Swift and Objective-C to make the simplest interface for artists and product personnel, and then they can directly call these encapsulated library functions in the application to immediately see the interface effect, so that the overall work efficiency will be improved, especially when combined with playgrounds, it will truly achieve what you see is what you get~

CocoaChina: iOS 8 has opened up many new features and introduced many APIs. Which of its features are you most concerned about? What are the special features of these features?

Zenny Chen: What I find more interesting are App Extensions and Handoff. As for App Extension, the App Store already has the popular Sogou Input Method and Baidu Input Method. This is a very revolutionary feature of iOS, and it breaks Apple's previous conservative attitude. Handoff is also a very interesting feature, which allows you to seamlessly present the current activity on another device while using an app on one device. This is very interesting.

The more practical new features include PhotoKit, HealthKit, HomeKit and CloudKit. HealthKit combined with Apple Watch can create a lot of interesting things. HomeKit will be helpful in the field of smart home; CloudKit is a good thing for online data synchronization. CloudKit is a good tool especially for some small and micro enterprises. Some stand-alone applications can directly use CloudKit for data storage and transmission without having to build a server by themselves.

Of course, for a grassroots fanatic like me, what excites me the most is Metal, haha.

CocoaChina: Have you developed game apps before? Have you learned about SceneKit and SpriteKit? If so, can you analyze why Apple launched them?

Zenny Chen: I have made some small games and some simple game engines in my spare time. I have used SpriteKit before. At present, its functions are still much weaker than Cocos2D-X. Of course, its advantage is that it can be developed directly in Objective-C and Swift. It also has its own particle editor, which is more convenient to use, but there seems to be a lot of room for improvement in performance. SpriteKit has been available since iOS 7.0. SceneKit is a new addition in 8.0. SceneKit mainly provides an upper-level interface for describing 3D scenes, and provides some 3D model imports, materials, lighting, physical collisions, particle effects, etc. However, I haven't started to try it yet, so I don't know its runtime performance.

I think Apple is pushing them to attract developers to inject fresh blood into the App Store. You see, the tools provided by Android are very limited, so many applications or games are relatively difficult to develop, which also leads to many companies still considering iOS as the primary development target platform, and Android as a backup.

CocoaChina: What is the difference between the new iOS graphics processing framework Metal and OpenGL ES? Can it pose a threat to it?

Zenny Chen: Metal provides a lower-level graphics interface than OpenGL, and is now targeted at the GPU of Apple A7 or newer processors. Since the PowerVR 6 series, GPUs have real general-purpose computing capabilities, so Metal has introduced Compute Shader in this version, which is quite good. Compute Shader was not introduced in OpenGL ES until version 3.1. Precisely because it is tailored to the GPU of Apple A series processors, Metal will execute faster than the general OpenGL ES, and the library capacity is also smaller, that is, the library code is lighter.

In the introduction of Metal features this time, we also saw that Metal's optimization effect on the Draw operation function is very significant. Metal's API is more similar to OpenCL. Although it is encapsulated in Objective-C, it will be very convenient to encapsulate it in pure C language (which meets the GNU11 extension of LLVM Clang, including support for Blocks syntax). And after using the entire API, I feel that the logic is very clear and there is no redundancy. It is just the operation steps of the entire rendering pipeline, haha. And as long as you know a little about OpenGL, you can get started quickly.

As for the threat to OpenGL ES, Apple is not Microsoft after all, so it will still strongly support open standards. I think Metal will coexist with OpenGL ES on iOS in the future. And Apple is unlikely to introduce OpenCL on iOS. If you want to use the GPU to do high-density general-purpose computing on iOS, you can directly use Metal's Compute Shader. So, I personally think that the introduction of Metal has actually opened up a new path to the field of GPU general-purpose computing.

I have used DirectX (9-11), OpenGL (2.1-4.1), OpenGL ES (1.1-3.0) and Metal, and I feel that Metal is the most practical. However, in terms of API encapsulation, Objective-C really combines simplicity and power, which may be one of the reasons why I feel it is easy to use. Of course, if you are not used to using Shader to write vertex calculations and pixel calculations, you can still use OpenGL ES1.1. Metal does not provide a fixed pipeline function like OpenGL ES1.1. So in this regard, I also think that Apple will not abolish OpenGL ES.

CocoaChina: What open source projects have you used in the development process? What problems have you encountered during the use?

Zenny Chen: I use relatively few open source projects in my development process. The biggest one is FFmpeg, which is used for processing audio and video and is used on Mac. In iOS projects, I have used minizip for file compression and decompression, as well as the Cocos2D-X game engine. In fact, the main problem with using third-party open source software is that it is well known that iOS updates quickly, and many open source projects may not be maintained after 2 or 3 years of maintenance. Then, when iOS is upgraded, there are all kinds of bugs and crashes. Therefore, only the code you master is the most secure. My requirements for my subordinates are very simple. Try to avoid using third-party things. If you use them, you must also understand what each line of code is doing in it to facilitate later maintenance. Of course, projects like Cocos2D-X that are constantly maintained by large companies can be used with confidence.

CocoaChina: How does learning about low-level technologies such as CPU and GPU help optimize iOS applications? In terms of improving performance, what optimization techniques are there for iOS applications?

Zenny Chen: Actually, for ordinary applications, performance tuning of the underlying technologies of CPU and GPU is not very helpful. As I mentioned when I talked about Metal, the performance tuning of the underlying technologies of CPU and GPU is mainly aimed at high-density computing, such as large-scale matrix multiplication (such as 1024x1024), image processing (filters, edge detection, smoothing, etc.), machine vision, video encoding and decoding (such as MPEG-4, H264, H265, VP8, etc.), in addition to some scientific computing, such as the DNN that we are currently hyping, DNA analysis in biological sciences, and molecular dynamics.

As for some games, they mostly rely on game engines, so there is not much room for optimization. For the optimization of most applications, the main means at present is to improve computing performance through multi-core and multi-threaded parallelism. In addition, network communication can be put into the user thread to avoid too much interference with the main thread used to process the UI.

CocoaChina: How should iOS developers plan their career development path? In addition to iOS, do they need to learn other technologies?

Zenny Chen: This is a very good question. I have been working for almost 10 years. I have only been working as an iOS professional developer for 3 years, haha. In fact, I think if you want to develop in the technical direction, then the first thing to do is to lay a good foundation. After laying a good foundation, you can cope with various new programming languages, various processors, and various operating system platforms. So I suggest that you consolidate the subjects you learned in traditional universities in your spare time, such as operating systems, data structures, mathematical logic, computer architecture, assembly language, C language, network communications, and databases. In addition, you can also familiarize yourself with HTML5 related technologies. After all, most of what iOS involves is in the field of mobile Internet, so it would be better if you have some knowledge of HTML5. If you feel that you have not learned C language well, you can consolidate it. C language is the mathematics in the field of computer programming. It is the ancestor language of all C-like programming languages, and you can see from the TIOBE ranking that it has always been ranked first. In addition, Objective-C is most seamlessly compatible with C language. From this point of view, C language is still very important.

The relationship between C, Objective-C and Swift is: Swift is a wrapper of Objective-C, although the wrapper has been changed so much that you really can't tell it is still a C-like language; while Objective-C is a wrapper of C language, adding object-oriented and reflection dynamic features on the basis of C language. Therefore, learning C well is very helpful for iOS development.

The above mainly talks about how iOS professional technical developers can further improve their technical capabilities. In fact, in the final analysis, it is to lay a good foundation, and then try to specialize in a more professional field, such as communications, 3D graphics, image recognition, etc. Because most people who do iOS are basically tinkering with the application layer. To be honest, the application layer can be basically mastered in one or two years, and continuing to do so will not improve the technology much.

Some iOS developers want to improve their status in the company. I think it depends largely on their understanding of the core business of the company. For small and medium-sized enterprises, product designers and planners cannot describe the product in detail. There are many places where developers need to expand their thinking on the design intent. If you have a good grasp of your company's corporate culture, work processes, and core business logic, you can make products that exceed expectations. In addition, if you handle interpersonal relationships well, it will not be difficult to improve your status.

Of course, I often meet young developers who are confused about the future and don’t know what path to take. So, I think it is important for those developers to calm down first, lay a good foundation, and then think about their future technical direction. After all, iOS development will be a popular technical position for a long time.

In order to move up to a higher position, in addition to technical skills, I think you also need to have control over products and even a sense of new market trends. Since you are already in this industry, you must learn how to keep learning and quickly respond to new market trends. Currently, app development is at the center of the rapidly developing and changing mobile Internet. Developers have the opportunity to create works that are trendy and even change the world. These experiences are valuable assets in themselves. As long as you lay a solid foundation, make adequate preparations, and seize opportunities, the future will definitely be bright.

Link to this article: http://www.cocoachina.com/programmer/20141010/9870.html