7.1.2. Functional overview

PowerVR technology is implemented as a display list renderer. Groups of polygons are batched together into a display list before being processed by the 3D rendering hardware. This is fundamentally different to the approach used by conventional systems, because it enables a scene to be partitioned into small tiles or regions, each of which is rendered independently. This has the following benefits:

Performance

Because the region is only a small subset of the whole scene, the ARM MBX HR-S can implement key operations on-chip without frequent access to external memory. Hidden Surface Removal (HSR), or Z-buffering, is done with an on-chip Z-buffer and display pixel processing and blending also uses an on chip frame buffer tile as a local storage. This means that the majority of external memory accesses normally performed by a conventional 3D system are eliminated. All the on-chip processing is performed at high depth and pixel accuracy at full clock rate, without having to wait for Z-buffer or frame buffer memory accesses that slow down conventional 3D systems.

Deferred texturing

In PowerVR systems, the HSR is completed in the first phase of the pipeline before texturing and shading. Because of this, only visible pixels to be finally drawn in the display memory are textured and shaded. This eliminates both the redundant work performed and, most importantly, the redundant texture fetches from memory required by conventional 3D systems.

Accuracy and image quality

Z-buffering and pixel blending are done entirely on-chip, so they can be performed at high precision with no performance degradation or increase in memory bandwidth requirements. In PowerVR all pixel blend operations are performed with true color precision, irrespective of the number of translucent layers or the bit-depth of the frame buffer (Internal True Color). This results in high image quality without performance loss

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