4D vector

In computer science, a 4D vector is a 4-component vector data type. Uses include homogeneous coordinates for 3-dimensional space in computer graphics, and red green blue alpha (RGBA) values for bitmap images with a color and alpha channel (as such they are widely used in computer graphics). They may also represent quaternions (useful for rotations) although the algebra they define is different.

Some microprocessors have hardware support for 4D vectors with instructions dealing with 4 lane single instruction, multiple data (SIMD) instructions, usually with a 128-bit data path and 32-bit floating point fields.

Specific instructions (e.g., 4 element dot product) may facilitate the use of one 128-bit register to represent a 4D vector. For example, in chronological order: Hitachi SH4, PowerPC VMX128 extension, and Intel x86 SSE4.

Some 4-element vector engines (e.g., the PS2 vector units) went further with the ability to broadcast components as multiply sources, and cross product support. Earlier generations of graphics processing unit (GPU) shader pipelines used very long instruction word (VLIW) instruction sets tailored for similar operations.

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