Texture mapping unit

A texture mapping unit (TMU) is a component in modern graphics processing units (GPUs). Historically it was a separate physical processor. A TMU is able to rotate, resize, and distort a bitmap image (performing texture sampling), to be placed onto an arbitrary plane of a given 3D model as a texture. This process is called texture mapping. In modern graphics cards it is implemented as a discrete stage in a graphics pipeline, whereas when first introduced it was implemented as a separate processor, e.g. as seen on the Voodoo2 graphics card. A texture mapping unit (TMU) is a component in modern graphics processing units (GPUs). Historically it was a separate physical processor. A TMU is able to rotate, resize, and distort a bitmap image (performing texture sampling), to be placed onto an arbitrary plane of a given 3D model as a texture. This process is called texture mapping. In modern graphics cards it is implemented as a discrete stage in a graphics pipeline, whereas when first introduced it was implemented as a separate processor, e.g. as seen on the Voodoo2 graphics card. The TMU came about due to the compute demands of sampling and transforming a flat image (as the texture map) to the correct angle and perspective it would need to be in 3D space. The compute operation is a large matrix multiply, which CPUs of the time (early Pentiums) could not cope with at acceptable performance. Today (2013), TMUs are part of the shader pipeline and decoupled from the Render Output Pipelines (ROPs). For example, in AMD's Cypress GPU, each shader pipeline (of which there are 20) has four TMUs, giving the GPU 80 TMUs. This is done by chip designers to closely couple shaders and the texture engines they will be working with. 3D scenes are generally composed of two things: 3D geometry, and the textures that cover that geometry. Texture units in a video card take a texture and 'map' it to a piece of geometry. That is, they wrap the texture around the geometry and produce textured pixels which can then be written to the screen.Textures can be an actual image, a lightmap, or even normal maps for advanced surface lighting effects. To render a 3D scene, textures are mapped over the top of polygon meshes. This is called texture mapping and is accomplished by texture mapping units (TMUs) on the videocard. Texture fill rate is a measure of the speed with which a particular card can perform texture mapping. Though pixel shader processing is becoming more important, this number still holds some weight. Best example of this is the X1600 XT. This card has a 3 to 1 ratio of pixel shader processors/texture mapping units. As a result, the X1600 XT achieves lower performance when compared to other GPUs of the same era and class (such as nVidia's 7600GT). In the mid range, texture mapping can still very much be a bottleneck.However, at the high end, the X1900 XTX has this same 3 to 1 ratio, but does just fine because screen resolutions top out and it has more than enough texture mapping power to handle any display. Textures need to be addressed and filtered. This job is done by TMUs that work in conjunction with pixel and vertex shader units. It is the TMU's job to apply texture operations to pixels. The number of texture units in a graphics processor is used when comparing two different cards for texturing performance. It is reasonable to assume that the card with more TMUs will be faster at processing texture information.In modern GPUs TMUs contain Texture Address Units(TA) and Texture Filtering Units(TF). Texture Address Units map texels to pixels and can perform texture addressing modes. Texture Filtering Units optionally perform hardware based texture filtering.