Both OpenGL and Vulkan are two of the most popular cross-platform graphics application programming interfaces or APIs out there. The two are also under the control of the Khronos Group. Both are used for rendering graphics via hardware acceleration. The main difference between the two is that the former is an older graphics API while the latter is positioned as the successor to the former. There are also more differences between OpenGL and Vulkan. These two have also been pitted because of the divergent graphics programming environment they each provide to software developers.
Understanding the OpenGL vs Vulkan Difference: A Comparison of Definitional Scope, Support and Compatibility, and Hardware Control
1. General Description and Historical Overview
Both are graphics APIs. This means that both act as a middleman between a software program or application and the discrete or integrated graphics processor of a computer. Software developers or graphics programmers use them to develop graphics-demanding programs or applications that can maximize the full potential of a graphics processor and lessen the workload on the central processing unit. Both also compete against platform-dependent and standard graphics APIs like Direct3D from Microsoft and of the Windows and Xbox platforms, and Metal from Apple and of the macOS, iOS and iPadOS, and tvOS platforms.
Silicon Graphics was the original author of OpenGL. It was first released in 1992. The control and further development were later transferred to the Khronos Group in 2006. Vulkan was co-developed by the Khronos Group together with AMD and EA Digital Illusions CE. It was first released to the public in 2016 as a successor to OpenGL. Take note that the Khronos Group has stopped providing support in OpenGL for new graphics technologies like ray tracing and deep learning. Other companies such as Apple deprecated support for OpenGL and did not bother supporting Vulkan in favor of its Metal graphics API.
2. Technical Details and Level of Abstraction
Another defining difference between OpenGL and Vulkan is that the former is used for rendering 2D and 3D graphics while the latter is used for rendering 3D graphics. Furthermore, although both are graphics APIs, Vulkan can also be considered both a graphics and compute API because it provides a unified set of tools for both graphics and compute tasks, and allows shaders to be used for graphics processing and general-purpose computation. To compare further, while OpenGL has a separate API for mobile called OpenGL ES, Vulkan has a unified API for both desktop or personal computer, mobile, and console platforms.
The level of abstraction is also a defining point in the OpenGL vs Vulkan debate. OpenGL has some low-level and high-level API aspects and Vulkan is specifically a low-level and low-overhead graphics API. A high-level API hides most of the internal workings of the system to focus on a user-friendly approach to development. It is easier to use but offers limited control. A low-level API exposes more of the intricate details and complexities of the system to allow more precise and ranula control over hardware features and functionalities. Hence, between the two, Vulkan has a steep learning curve but offers better optimization.
3. Platform Compatibility and Hardware Support
Remember that both graphics APIs are cross-platform. This means that they are supported in a variety of operating systems and devices, and are not platform-dependent, unlike Direct3D from Microsoft and Metal from Apple. OpenGL is compatible with Windows, Linux, and Android. It was once directly compatible with macOS and iOS but Apple deprecated support in favor of its Metal graphics API. Vulkan is compatible with Windows, Linux, BSD Unix, Android, Nintendo Switch, Raspberry Pi, Haiku, and Fuchsia. Both can still run on Apple platforms but would require using third-party porting layers that wrap over Metal.
Most manufacturers such as AMD, Intel, and Nvidia have drivers for both OpenGL and Vulkan. This is specifically true for most modern graphics processors roughly from 2012 and onwards. However, because the Khronos Group has dropped support for new graphics technologies in OpenGL, this graphics API might not be able to utilize the new features and capabilities of newer graphics processors. Vulkan is newer and has support for new graphics technologies, but older processors might not support it or its newer versions might not be supported even in newer hardware. It is also not backward compatible with OpenGL.
4. Graphics Processor and Central Processor Usage
The OpenGL vs Vulkan discussion also includes how the two differ in terms of CPU usage. Vulkan is considered more effective and efficient because it takes advantage of the multi-core and multi-threaded design of modern CPUs. OpenGL does not scale well with multi-core CPUs. Execute calls are also not cached and some aspects of the graphics pipeline are handled internally in OpenGL. These can put more strain on the CPU. Vulkan uses command buffers and enables developers to offload workload from the CPU to the GPU. These can result in better performance and improved responsiveness in CPU-bound scenarios.
Both use compute shaders to make the most out of the capabilities of graphics processors. However, when it comes to the utilization of these shaders, the two manage them differently. OpenGL uses the C++ programming language with its GLSL compiler. This compiler runs at the driver level and writes the shaders. The shaders would be translated into machine code by the application runtime. The code varies for each driver. Vulkan shortens this process and saves the GPU from using different translators. It uses a standard translator tool that can translate codes from other languages into a universal format called SPIR-V.
5. Developer Control Over Memory Management
Another difference between the two graphics APIs is how they handle memory management for graphics processing. OpenGL does not provide developers or programmers with control over system memory because the graphics driver takes care of memory management. This can be inefficient because a particular driver uses heuristics or has internal rules for deciding how to allocate memory. These rules can vary between graphics processors. The memory allocations might also be unsuitable for the particular needs of a program or app. This can result in underperformance when resources are moved in memory.
Vulkan allows developers or programmers to have fine-grained control over the system memory. A developer can see the different types of memory available on the system and choose the most ideal based on its needs. A prime example is choosing between fast memory with a smaller size and slower memory with a larger size for frequently used data versus less frequently used data. This level of control enables better software-hardware optimization of memory usage according to the theoretical demands of the program or app and allows better real-world performance. Remember that Vulkan is a low-level application programming interface.
Takeaways from the OpenGL vs Vulkan Discussion: Comparing the Performance and Specific Applications of the Two Graphics APIs
Nevertheless, based on the aforementioned difference between OpenGL and Vulkan, especially in terms of their general descriptions, technical details, level of abstraction, platform compatibility and hardware support, processor usage, and memory management, these two graphics APIs provide developers or programmers with different development environments. It is important to highlight that the OpenGL vs Vulkan discussion centers on the fact that the former has some low-level and high-level aspects while Vulkan is a low-level graphics API. This core distinction affects the time and effort needed to develop programs or apps.
It is easier to develop using OpenGL because it takes away some of the complexities that come from controlling hardware features and functions. Furthermore, because it handles some aspects of the graphics pipeline internally, debugging can be generally easier. Vulkan has a steeper learning curve and can cost developers or programmers more time and effort. Using this graphics API is tantamount to developing from scratch. It requires a deeper understanding of hardware constructs and implementing this understanding. This disadvantage comes from the fact that it enables a higher degree of fine-grained control over hardware resources.
The graphics performance difference between OpenGL and Vulkan is not definite. Vulkan is better than OpenGL in terms of raw performance potential because of the low-level abstraction that provides more hardware control, better utilization of multi-core and multi-threaded processor architecture, and a shorter process of translating and utilizing different shaders. However, because the performance gains are theoretical, performance is not guaranteed and is still dependent on the capabilities of the developers or programmers. A program developed using OpenGL can still perform better than a counterpart developed with Vulkan.
Both OpenGL and Vulkan are cross-platform graphics APIs and each has a respectable amount of community support and resources. The two also have third-party porting layers. Nevertheless, in consideration of the differences between the two, OpenGL can be considered a better choice for simpler projects or when ease of development is a priority. This graphics API is also ideal for beginners who want to learn graphics programming for the first time because it provides foundational concepts that can be applied to other graphics APIs. However, for projects that require maximizing the potential of hardware components, or for a general requirement that centers on future-proofing, Vulkan might be a more suitable choice.
