Challenges of the X Render Extension
Keith Packard
XFree86 Core Team
keithp@keithp.com
2001-10-17

The X Render Extension provides an entirely new graphics architecture for the X Window System. In the process of developing the new rendering primitives, several interesting issues were uncovered. The first was in completing the image compositing algebra used as the underlying pixel manipulation mechanism. Next, an exact specification was required for anti-aliased polygons. Finally, the ubiquity of sub-pixel addressable displays suggested that the extension incorporate operations that could take full advantage of them.
X Render Extension为XWindow系统提供了一个全新的图形架构。在开发新一代渲染图元(rendering primitives)的过程中，出现了多个有趣的问题。首先是把图形合成计算(image compositing algebra)作为底层像素的处理机制。其次是，反走样多边形(anti-aliased polygons)需要制定一个更精确的规范。最后，扩展混合运算(extension incorporate operations)应该好好利用随处可见的次像素可寻址显示技术(sub-pixel addressable displays)。

一些建议(plt):
(several interesting issues were uncovered.) 翻译为: 一些有趣的问题被发现。
Finally, the ubiquity of sub-pixel addressable displays suggested
that the extension incorporate operations that could take full advantage
of them.
翻译为：最后，子像素可寻址显示技术的广泛使用表明扩展混合运算可以充分的利用这一技术。


The underlying rasterization system in Render is an extension of that found in the Plan-9 window system. That system provides only for the Porter/Duff "over" operator. Render starts with the complete Porter/Duff operator set and extends it further. The full set of Render compositing primitives is presented along with justification and some examples.
渲染器的底层光栅化系统是Plan-9系统渲染器的一个插件。这一系统只提供通过操作符的Porter/Duff(???看门人和水果补丁???)。渲染器一开始就拥有完整的Porter/Duff操作而且扩展了它。用来混合图元的一系列渲染器与其说明和范例一同发布。

一些建议(plt):
渲染器底层的光栅化系统是Plan-9窗口系统中光栅化系统的一个扩展。
原来的系统只提供了对操作符的Porter/Duff。
渲染器从一开始就支持完整的Porter/Duff操作并对其作了进一步的扩展。
完整的渲染器混合图元集与其说明和范例一同发布。


Over the last fifteen years, numerous X applications have demonstrated that X clients must be able to accurately predict and emulate the rasterization operations performed within the server -- largely to supplant server-side rendering with client-side operations when the X protocol proves insufficient. The geometric primitives in Render are exactly specified, however the original specification was shown to require an inordinate amount of computation. Requirements for any solution are justified and a simplified specification which meets these requirements is presented.
在最近的15年内，众多的X应用软件已经证明，X客户端必须能准确地预测和模拟服务端内的光栅操作，当X协议被证明是低效率时，就要用客户端渲染来替代服务端渲染。渲染器内的几何图元(geometric primitives)是被准确规定的，但是从原先的规范看来，需要大量多余的计算。任何解决方案都要有合乎情理的计算量。符合这一要求的简化版规范已经出现。

Finally, the compositing infrastructure was extended to provide for separate rendering control of the red, green and blue components of each pixel. This is used by the Xft library to rasterize glyphs that improve appearance of text on sub-pixel addressable displays such as digital LCD panels. A description of this operation is presented along with the algorithms used to rasterize glyphs.
最后，底层的混合结构被扩展成可以对一个像素的RGB分别渲染，Xft使用它来光栅化方字形，来改善次像素可寻址显示文字的效果，比如LCD显示器。对这一操作的说明以及用来对方字形光栅计算的算法一起发布了。


一些修正建议(plt):
来改善在次像素可寻址显示器上文字显示的效果。

本文档为幻灯片：
原文：
http://keithp.com/~keithp/talks/renderproblems/renderproblems/render-title.html
译文：
http://www.fly19.net/applepie/render/render-title.html

翻译人员：applepie