How SDL Accelerates Video Output under Linux.

What we might know about the Linux, X-server, is that it offers pure X-protocol to render such features efficiently to the display, as Text with Fonts, Simple GUI-elements, and small Bitmaps such as Icons… But then, when it’s needed to send moving pictures to the display, we need extensions, which serious Linux-users take for granted. One such extension is the Shared-Memory extension.

Its premise is that the X-server shares a region of RAM with the client application, into which the client-application can draw pixels, which the X-server then transfers to Graphics Memory.

For moving pictures, this offers one way in which they can also be ~accelerated~, because that memory-region stays mapped, even when the client-application redraws it many times.

But this extension does not make significant use of the GPU, only of the CPU.

And so there exists something called SDL, which stands for Simple Direct Media Layer. And one valid question we may ask ourselves about this protocol, is how it achieves a speed improvement, if it’s only installed on Linux systems as a set of user-space libraries, not drivers.

(Updated 10/06/2017 : )

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Understanding that The GPU Is Real

A type of graphics hardware which once existed, was an arrangement by which a region of memory was formatted to correspond directly to screen-pixels, and by which a primitive set of chips would rasterize that memory-region, sending the analog-equivalent of pixel-values to an output-device, such as a monitor, even while the CPU was writing changes to the same memory-region. This type of graphics arrangement is currently referred to as “A Framebuffer Device”. Since the late 1990s, these types of graphics have been replaced by graphics, that possess a ‘GPU’ – a Graphics Processing Unit. The acronym GPU follows similarly to how the acronym ‘CPU’ is formed, the latter of which stands for Central Processing Unit.

A GPU is essentially a kind of co-processor, which does a lot of the graphics-work that the CPU once needed to do, back in the days of framebuffer-devices. The GPU has been optimized, where present, to give real-time 2D, perspective-renderings of 3D scenes, that are fed to the GPU in a language that is either some version of DirectX, or in some version of OpenGL. But, modern GPUs are also capable of performing certain 2D tasks, such as to accelerate the playback of compressed video-streams at very high resolutions, and to do Desktop Compositing.

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What they do is called raster-based rendering, as opposed to ray-tracing, where ray-tracing cannot usually be accomplished in real-time.

And modern smart-phones and tablets, also typically have GPUs, that give them some of their smooth home-screen effects and animations, which would all be prohibitive to program under software-based graphics.

The fact that some phone or computer has been designed and built by Apple, does not mean that it has no GPU. Apple presently uses OpenGL as its main language to communicate 3D to its GPUs.

DirectX is totally owned by Microsoft.

The GPU of a general-purpose computing device often possesses additional protocols for accepting data from the CPU, other than DirectX or OpenGL. The accelerated, 2D decompressed video-streams would be an example of that, which are possible under Linux, if a graphics-driver supports ‘vdpau‘ …

Dirk