less_retarded_wiki/sw_rendering.md

# Software Rendering

Sofware (SW) rendering refers to [rendering](rendering.md) [computer graphics](graphics.md) without the help of [graphics card](gpu.md) (GPU), i.e. computing images only with [CPU](cpu.md). This mostly means rendering [3D](3d.md) graphics but can also refer to other kinds of graphics such as drawing [fonts](font.md) or [video](video.md). Before GPUs were invented, all rendering was done in software, of course -- games such as [Quake](quake.md) were designed with SW rendering and only added possible GPU acceleration later. SW rendering for traditional 3D graphics is also called software [rasterization](rasterization.md).

SW rendering has advantages and disadvantages. Firstly it is **much slower** -- GPUs are designed to perform graphics-specific operations very quickly and, more importantly, they can compute many pixels in [parallel](parallelism.md), while a CPU has to compute pixels sequentially one by one and that in addition to all other computations it is otherwise performing. This causes a much lower [FPS](fps.md). For this reasons SW rendering is also normally of **lower quality** (lower resolution, [nearest neighbour](nn.md) interpolation, ...) to allow at least somewhat workable FPS.

On the other hand SW rendering is more [portable](portability.md) (as it can be written in a portable language such as [C](c.md)), less [bloated](bloat.md) and **eliminates the [dependency](dependency.md) on GPU** so it will be supported almost anywhere as every computer has a CPU, while not all computers (such as [embedded](embedded.md) devices) have a GPU (or, if they have it, it may not be sufficient, supported or have a required [driver](driver.md)). SW rendering may also be implemented in a simpler way and it may be easier to deal with as there is e.g. no need to write [shaders](shader.md) in a special language, manage transfer of data between CPU and GPU or deal with parallel programming. It is the [KISS](kiss.md) approach.

A lot of software and rendering frameworks offer both options: accelerated rendering using GPU and SW rendering as a [fallback](fallback.md) (in case the first option is not possible). Sometimes there exists a rendering [API](api.md) that has both an accelerated and software implementation (e.g. [TinyGL](tinygl.md) for [OpenGL](opengl.md)).

For simpler and even somewhat more complex graphics **purely software rendering is a lot of times the best choice**. [LRS](lrs.md) suggests you prefer this kind of rendering for its simplicity and portability, at least as one possible option. On devices with lower resolution not many pixels need to be computed so SW rendering can actually be pretty fast despite low specs, and on "big" computers there is nowadays usually an extremely fast CPU available that can handle comfortable FPS at higher resolutions. There is a LRS software renderer you can use: [small3dlib](s3l.md).

Note that SW rendering doesn't mean we are not using [GPU](gpu.md) at all, in fact most personal computers nowadays **require** some kind of GPU to even display anything. SW rendering only means that computation of the image to be displayed doesn't use any hardware specialized for this purpose.

Some SW renderers make use of specialized CPU instructions such as [MMX](mmx.md) which can make SW rendering faster thanks to handling multiple data in a single step. This is kind of a mid way: it is not using a GPU per se but only a mild form of hardware acceleration. The speed won't reach that of a GPU but will outperform a "pure" SW renderer. However the disadvantage of a hardware dependency is still present: the CPU has to support the MMX instruction set. Good renderers only use these instructions optionally and fall back to general implementation in case MMX is not supported.