Editing PowerVR (section)

== Technology ==
The PowerVR chipset uses a method of 3D rendering known as ''[[tile-based deferred rendering]]'' (often abbreviated as TBDR) which is tile-based rendering combined with PowerVR's proprietary method of Hidden Surface Removal (HSR) and Hierarchical Scheduling Technology (HST). As the polygon generating program feeds triangles to the PowerVR (driver), it stores them in memory in a [[triangle strip]] or an indexed format. Unlike other architectures, polygon rendering is (usually) not performed until all polygon information has been collated for the current [[Video frame|frame]]. Furthermore, the expensive operations of texturing and shading of pixels (or fragments) is delayed, whenever possible, until the visible surface at a pixel is determined — hence rendering is deferred.

In order to render, the display is split into rectangular sections in a grid pattern. Each section is known as a tile. Associated with each tile is a list of the triangles that visibly overlap that tile. Each tile is rendered in turn to produce the final image.

Tiles are rendered using a process similar to [[ray-casting]]. Rays are numerically simulated as if cast onto the triangles associated with the tile and a pixel is rendered from the triangle closest to the camera. The PowerVR hardware typically calculates the depths associated with each polygon for one tile row in 1 cycle.{{dubious|date=April 2013}}

This method has the advantage that, unlike a more traditional early Z rejection based hierarchical systems, no calculations need to be made to determine what a polygon looks like in an area where it is obscured by other geometry. It also allows for correct rendering of partially transparent polygons, independent of the order in which they are processed by the polygon producing application. (This capability was only implemented in Series 2 including Dreamcast and one MBX variant. It is generally not included for lack of API support and cost reasons.)
More importantly, as the rendering is limited to one tile at a time, the whole tile can be in fast on-chip memory, which is flushed to video memory before processing the next tile. Under normal circumstances, each tile is visited just once per frame.

PowerVR is a pioneer of tile based deferred rendering. Microsoft also conceptualized the idea with their abandoned [[Microsoft Talisman|Talisman]] project. Gigapixel, a company that developed IP for tile-based 3D graphics, was purchased by [[3dfx]], which in turn was subsequently purchased by [[Nvidia]]. Nvidia has now been shown to use tile rendering in the Maxwell and Pascal microarchitectures for a limited amount of geometry.<ref>{{Cite web|url=https://www.anandtech.com/show/10536/nvidia-maxwell-tile-rasterization-analysis|title=Hidden Secrets: Investigation Shows That NVIDIA GPUs Implement Tile Based Rasterization for Greater Efficiency|first=Ryan|last=Smith|website=www.anandtech.com}}</ref>

[[ARM Holdings|ARM]] began developing another major tile based architecture known as [[Mali (GPU)|Mali]] after their acquisition of [[Falanx]].

Intel uses a similar concept in their integrated graphics products. However, its method, called zone rendering, does not perform full [[hidden surface removal]] (HSR) and deferred texturing, therefore wasting fillrate and texture bandwidth on pixels that are not visible in the final image.

Recent advances in hierarchical Z-buffering have effectively incorporated ideas previously only used in deferred rendering, including the idea of being able to split a scene into tiles and of potentially being able to accept or reject tile sized pieces of polygon.

Today, the PowerVR software and hardware suite has ASICs for [[video encoding]], [[video decoding|decoding]] and associated [[image processing]]. It also has virtualisation, and [[DirectX]], [[OpenGL ES]], [[OpenVG]], and [[OpenCL]] acceleration.<ref>[https://www.engadget.com/2011/06/02/texas-instruments-announces-multi-core-1-8ghz-omap4470-arm-proc/ Texas Instruments announces multi-core, 1.8GHz OMAP4470 ARM processor for Windows 8], By Amar Toor, June 2, 2011, Engadget</ref>
Newest PowerVR Wizard GPUs have [[graphics pipeline|fixed-function]] [[Ray-tracing hardware|Ray Tracing]] Unit (RTU) hardware and support hybrid rendering.<ref>{{Cite web|url=https://www.imaginationtech.com/graphics-processors/|title=PowerVR - embedded graphics processors powering iconic products|website=Imagination}}</ref>