If you are a 3D graphics designer or a game developer, you must have heard of OpenGL and Vulkan. Both the APIs are used widely for various applications.
However, it is important to know the key differences between the two APIs in terms of compatibility, features and performance so that you can make the right choice between the two. In this article, we’ll explain these differences in detail.
Here’s what we will cover:
- What is OpenGL?
- What is Vulkan?
- OpenGL vs Vulkan: Key differences
- OpenGL vs Vulkan: Which one should you choose?
What is OpenGL?
OpenGL, short for Open Graphics Library, was introduced in 1992 by Silicon Graphics Inc. It has become widely employed in the realms of game development, computer-aided design (CAD), and virtual reality applications.
Due to its status as a low-level API, developers are afforded direct access to the hardware, enabling them to fine-tune programming codes for specific hardware requirements. Consequently, OpenGL proves particularly well-suited for seasoned programmers and developers.
An additional noteworthy characteristic of OpenGL is its state-based nature. This implies that the API maintains a predetermined set of variables to facilitate graphic rendering. Nonetheless, developers retain the flexibility to modify these variables according to their specific needs, making OpenGL a preferred choice among experienced developers.
Moreover, OpenGL is compatible with various platforms such as Windows, Linux, macOS, Android, and iOS. It is important to note, however, that the API requires additional libraries to operate on these platforms. While this may result in minor compatibility issues, they are typically not of significant magnitude.
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What is Vulkan?
Despite its many advantages, OpenGL suffered from several shortcomings such as limited autonomy to the developers. To overcome these shortcomings, Khronos Group launched Vulkan in 2016 as a ‘next-generation OpenGL’ API.
Vulkan is also a low-level API and is based on a command buffer, which means that developers can submit commands to define the specific aspects of rendering such as draw calls, the pipeline state, and the memory barriers, among others.
Vulkan is comparable to Apple’s Metal API and Microsoft’s DirectX but it is a steep learning curve. As it gives more control to developers, it is favoured more than OpenGL. Moreover, it is more efficient than OpenGL and reduces the CPU load via the use of a technique known as batching.
Furthermore, Vulkan offers multi-thread CPU support that OpenGL lacks. It also features advanced technologies like Ray Tracing and hence is used for 2D and 3D rendering.
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OpenGL vs Vulkan: Key differences
Let us dive into the key differences between the two APIs based on several parameters:
Performance
As Vulkan is faster and more efficient than OpenGL, it allows for better parallelism and multithreading support. Furthermore, Vulcan offers better memory management support to the developers along with graphics synchronisation.
Design
OpenGL isn’t suited for normal desktop computers as it is designed for workstations. Also, it is not suitable for tablets and smartphones due to the parallel command inhibiting threading model.
On the other hand, Vulkan can run on almost all platforms including tablets and smartphones. It is designed to deliver exceptional performance, code validation and debugging on any platform.
Furthermore, Vulkan offers developers more control over GPU and relies on command buffers thereby lessening the time.
CPU utilisation
As Vulkan uses a command buffer, it efficiently utilises CPU cores and increases efficiency. On the other hand, OpenGL is not cached thus requiring frequent interactions with the kernel mode to change and validate the state of the graphics driver.
The second distinguishing factor lies in Vulkan’s capability for parallel buffer generation. This feature enables Vulkan to leverage the computational power of all available CPU cores, addressing a limitation that OpenGL encountered. OpenGL was designed in an era when processors typically had a single core, and the concept of multiple-core processors was unprecedented. In contrast, with contemporary processors commonly equipped with at least eight cores, Vulkan stands out as the sole API adept at effectively harnessing the potential offered by these multi-core architectures.
Shader compilers
In the context of OpenGL, the programming language employed is C++, a high-level language. Complementing this, a GLSL compiler operates at the driver level, producing shaders that serve as directives for the graphics card in rendering visual elements. Subsequently, during execution, the application runtime translates these shaders into machine code, facilitating their interpretation by the GPU for actual display.
In contrast, Vulkan streamlines this process through the utilisation of a standardised intermediate representation known as SPIR-V. Vulkan incorporates a compiler-source translator, extending support beyond GLSL to include HLSL and LLVM. This translator converts code from diverse high-level APIs into SPIR-V, which is then used directly by Vulkan in the shader stage. Noteworthy is Vulkan’s compatibility with various domain-specific languages, tools, frameworks, and even OpenGL C kernels, enhancing its versatility in graphics programming.
Predictability
In OpenGL, there’s a high level of abstraction, meaning that many things happen automatically without the programmer having to explicitly write code for each action. These behind-the-scenes operations involve managing resources (like memory), checking for errors and making sure everything is valid, preparing shaders in advance, and coordinating some tasks to work together smoothly.
While this design makes it convenient for developers by reducing the amount of code they need to write, it also introduces an element of unpredictability. You might not always know exactly how your code will behave until you see the results. Another thing to note is that the graphics driver, a special software that helps your computer’s hardware talk to the software, decides when to process certain tasks. This decision-making by the driver can sometimes cause interruptions in the rendering process, which is the creation of images on your screen.
On the other hand, Vulkan does things a bit differently. It’s what we call an explicit API, which means that, unlike OpenGL, it doesn’t have the graphics driver keeping track of resources or deciding how they’re related. Instead, this responsibility falls on the application, and the developer needs to write code for each step of the process.
The benefit of this approach is that tasks, or ‘jobs,’ are sent in advance for execution. This makes the processing of tasks in Vulkan more predictable and efficient. As a result, when you’re creating images or graphics in Vulkan, you don’t experience the delays and interruptions that can sometimes happen in OpenGL. It’s like Vulkan is a well-organised manager, getting all the work lined up beforehand, so things run smoothly without unexpected pauses or hitches in the visual experience.
Driver and application layer
In OpenGL, which is an implicit API, the responsibility for managing resources like memory and keeping track of the current state of graphics operations is handled by the driver layer of the computer. This means that the part of the software directly controlled by the application—the application layer—doesn’t have to do much. However, because of this setup, rendering images or graphics can take longer than it might if more of the resource management tasks were done by the application itself.
On the other hand, Vulkan is designed to be as close to the actual graphics hardware of your computer as possible. To achieve this, it puts the responsibility of managing resources, logic, and states into the hands of the applications or software that developers create.
By letting the application layer handle resource allocation, Vulkan gives the developers full control over the computer’s resources. This direct control allows the software to communicate with the graphics processor (GPU) more efficiently, making the GPU render images as quickly as possible. Ultimately, this design in Vulkan can lead to improved graphics performance and overall processor efficiency.
Applications developer control
In OpenGL, developers have limited control over the computer’s memory, as the drivers decide how to allocate resources, leading to potential inefficiencies.
In contrast, Vulkan provides more control by allowing developers to directly manage memory types, extensions, command buffer queues, and physical devices. This flexibility allows developers to optimise Vulkan’s behavior for their specific application needs, without interference from the driver.
Multithread scalability
OpenGL, the older graphics technology, struggles with utilising the full processing power of modern CPUs because it doesn’t handle multiple tasks well at the same time. This limitation results in high CPU overhead, meaning the CPU has to work extra hard to handle graphics-related tasks efficiently.
On the flip side, Vulkan, the newer technology, is designed to work well with the modern capabilities of CPUs. It takes full advantage of a computer’s ability to handle multiple tasks simultaneously, a concept known as multithreading. Vulkan intentionally organises and controls tasks so they can be done concurrently in different threads, from their creation to their execution. This explicit approach allows Vulkan to make better use of the processing power of modern CPUs, providing more efficient and smoother performance.
Cross-platform game porting
In OpenGL, game porting between desktop and mobile platforms is difficult due to separate APIs for each platform.
Vulkan, in contrast, offers a unified API for both desktop and mobile, making game development and porting more seamless. Vulkan also provides better tools and prioritises mobile platforms, making it a more flexible and efficient choice for game developers.
Error checking
In OpenGL, the system automatically checks for errors as part of its normal functioning. However, this constant checking can slow down applications, even when they are running smoothly. The PC might be burdened with excessive and random error checks, impacting its performance.
In Vulkan, error checking works differently. It’s like an optional extra feature that developers can turn on or off as needed. During the development phase, when programmers are working on the game or application, they can enable these error checks to help find and fix problems (debugging). But when the game is finished and ready to be used by others, these checks can be turned off to ensure the application runs at its best without unnecessary slowdowns caused by constant error monitoring.
| Aspect | OpenGL | Vulkan |
|---|---|---|
| Performance | Slower, less efficient | Faster, better parallelism and multithreading |
| Design | Suited for workstations, not tablets/smartphones | Unified API for all platforms, including tablets/smartphones |
| CPU utilisation | Less efficient, not cached | Efficient use of CPU cores, explicit multithreading |
| Shader compilers | GLSL compiler at the driver level | SPIR-V intermediate representation, more versatile |
| Predictability | High abstraction level, unpredictable | Explicit API, more predictable and efficient |
| Driver and app layer | Driver-managed resources | App layer manages resources, more control |
| Developer control | Limited control over memory allocation | Full control over memory, extensions, and devices |
| Multithread scalability | Poor multithreading capacity | Designed for efficient multithreading, better CPU utilisation |
| Game porting | Separate APIs for desktop and mobile | Unified API, better tools, prioritises mobile |
| Error checking | Automatic and constant checking | Optional, can be turned on/off for debugging |
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OpenGL vs Vulkan: Which one should you choose?
Both OpenGL and Vulkan are powerful APIs and depending on your project you can choose any one of these. Keep in mind the hardware and platform as OpenGL works best on Windows and Linux.
Also, keep in mind your expertise level as to use Vulkan, you need a steep learning curve. Also, Vulkan allows more control over resources and provides more efficiency.
We hope that this article has helped you in understanding the differences between OpenGL and Vulkan.
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