display:高通display overview

ViG     pipe –For video and graphics
RGB   pipe –For graphics
DMA   pipe –For graphics and rotation

这些pipe会在sdm对图像做出决策后对应不同的image。

高通的display overview原文档部分贴出

什么是overlay

1. Overlay（覆盖）是一种数字视频的显示技术，它允许数字信号不经过显示芯片(GPU)处理，而直接通过显存输出到显示器屏幕上。Overlay显示模式最大的用途在于优化视频播放。

2. A hardware overlay is a dedicated area of video memory that can be overlayed on the primary surface. No copy is performed when the overlay is displayed. The overlay operation is performed in hardware, without modifying the data in the primary surface.
   一个hardware overlay是一个专门的视频内存区域，可以覆盖在primary surface之上。显示overlay图时不执行复制。overlay操作由硬件执行，不修改在primary surface的数据。
   
   The use of hardware overlays for video playback was common in earlier versions of Windows, because overlays are efficient for video content with a high frame rate. Starting in Windows 7, Direct3D 9 supports hardware overlays. This support is intended primarily for video playback, and differs in some respects from earlier DirectDraw APIs:
   在早期的Windows版本中，使用硬件覆盖[overlay]进行视频回放是很常见的，因为覆盖[overlay]对于高帧率的视频内容非常有效。从Windows 7开始，Direct3D 9支持硬件覆盖[overlay]。这种支持主要用于视频回放，在某些方面与之前的DirectDraw api有所不同:
   
   The overlay cannot be shrunk, mirrored, or deinterlaced.
   Source color keys and alpha blending are not supported.
   Overlays can be stretched if the overlay hardware supports it. Otherwise, stretching is not supported. In practice, not all graphics drivers support stretching.
   Each device supports at most one overlay.
   Overlay is performed using a destination color key, but the Direct3D runtime automatically selects the color and draws the destination rectangle. Direct3D automatically tracks the position of the window and updates the overlay position whenever the PresentEx is called.

 primary surface，在weston的合成逻辑里面，这个就是GPU需要合成的那些surface

 特定名词

1.5 Acronyms, abbreviations, and terms
Table 1-1 provides definitions for the acronym