Anti aliasing 抗锯齿 后期处理系列5

Anti aliasing 抗锯齿

本文档主要是对Unity官方手册的个人理解与总结（其实以翻译记录为主：>）
仅作为个人学习使用，不得作为商业用途，欢迎转载，并请注明出处。
文章中涉及到的操作都是基于Unity2018.3版本
参考链接：https://github.com/Unity-Technologies/PostProcessing/wiki/Anti-aliasing

The Anti-aliasing effect offers a set of algorithms designed to prevent aliasing and give a smoother appearance to graphics. Aliasing is an effect where lines appear jagged or have a “staircase” appearance (as displayed in the left-hand image below). This can happen if the graphics output device does not have a high enough resolution to display a straight line.
抗锯齿效果提供了一套算法，旨在防止锯齿，并给图形一个更平滑的外观。锯齿是线条呈现锯齿状或有“楼梯”外观的效果(如下面的左图所示)。如果图形输出设备没有足够高的分辨率来显示直线，就会发生这种情况。

Anti-aliasing reduces the prominence of these jagged lines by surrounding them with intermediate shades of color. Although this reduces the jagged appearance of the lines, it also makes them blurrier.
抗锯齿通过在锯齿线周围添加中间色调来降低锯齿线的突出度。虽然减少了线条的锯齿状外观，但也使它们更加模糊。

The Anti-aliasing algorithms are image-based. This is very useful when traditional multisampling (as used in the Editor’s Quality settings) is not properly supported or when working with specular-heavy PBR materials.
抗锯齿算法是基于图像的。当传统的多采样(如在编辑器的质量设置中使用的)没有得到适当的支持，或者在处理大量高光的PBR材质时，这是非常有用的。

The algorithms supplied in the post-processing stack are:
后处理栈中提供的算法为:

• Fast Approximate Anti-aliasing (FXAA) 快速近似抗锯齿
• Subpixel Morphological Anti-aliasing (SMAA) 次像素形态抗锯齿
• Temporal Anti-aliasing (TAA) 随机采样抗锯齿

They are set per-camera on the Post-process Layer component.
它们是在后期处理层组件上按相机设置的。

Fast Approximate Anti-aliasing 快速近似抗锯齿(FXAA)

FXAA is the cheapest technique and is recommended for mobile and other platforms that don’t support motion vectors, which are required for TAA.
FXAA是最便宜的技术，推荐用于移动平台和其他不支持运动矢量的平台，这是TAA所必需的平台。

Property	Function
Fast Mode	A slightly lower quality but faster variant of FXAA. Highly recommended on mobile platforms.
快速模式	一种稍低质量但更快的FXAA变种。强烈推荐在移动平台。
Keep Alpha	Toggle this on if you need to keep the alpha channel untouched by post-processing. Else it will use this channel to store internal data used to speed up and improve visual quality.
保留Alpha	如果您需要保持alpha通道不受后处理的影响，请开启此选项。否则，它将使用这个通道来存储内部数据，用于加快和提高效果质量。

Performances

Fast Mode should be enabled on mobile & Nintendo Switch as it gives a substantial performance boost compared to the regular mode on these platforms. PS4 and Xbox One slightly benefit from it as well but on desktop GPUs it makes no difference and the regular mode should be used for added visual quality.
快速模式应该在移动和任天堂Switch上启用，因为与这些平台上的常规模式相比，它提供了显著的性能提升。PS4和Xbox One也可从中获得了些许好处，但在桌面GPUs上，并没有什么不同，应该用常规模式增加效果质量。

Requirements

• Shader Model 3

Subpixel Morphological Anti-aliasing 次像素形态抗锯齿

SMAA is a higher quality anti-aliasing effect than FXAA but it’s also slower. Depending on the art-style of your game it can work as well as TAA while avoiding some of the shortcomings of this technique.
SMAA比FXAA有更高质量的抗锯齿效果，但是速度也慢。根据游戏的美术风格，它可以像TAA一样工作，同时避免这种技术的一些缺点。

• Quality The overall quality of the anti-aliasing filter. 抗锯齿过滤的整体质量。

Performances
Lowering the Quality setting will make the effect run faster. Using SMAA on mobile platforms isn’t recommended.
降低质量设置将使效果运行得更快。不建议在移动平台上使用SMAA。

Known issues and limitations 已知问题和限制

• SMAA doesn’t support AR/VR.

Requirements

• Shader Model 3

Temporal Anti-aliasing 随机采样抗锯齿

TAA is a more advanced anti-aliasing technique where frames are accumulated over time in a history buffer to be used to smooth edges more effectively. It is substantially better at smoothing edges in motion but requires motion vectors and is more expensive than FXAA. Due to this it is recommended for desktop and console platforms.
TAA是一种更高级的抗锯齿技术，它将帧累积在历史缓冲区中，以便更有效地平滑边缘。它在平滑运动中的边缘方面做得更好，但需要运动矢量，而且比FXAA更昂贵。因此，建议将其用于桌面和主机平台。

Property	Function
Jitter Spread	The diameter (in texels) inside which jitter samples are spread. Smaller values result in crisper but more aliased output, whilst larger values result in more stable but blurrier output.
抖动扩大	抖动采样扩大的直径(以texels为单位)。较小的值会产生更清晰但更锯齿化的输出，而较大的值会产生更稳定但更模糊的输出。
Stationary Blending	The blend coefficient for stationary fragments. Controls the percentage of history sample blended into final color for fragments with minimal active motion.
静止融合	静止碎片的混合系数。控制具有最小活动的片段的历史采样融合成最终颜色的百分比。
Motion Blending	The blending coefficient for moving fragments. Controls the percentage of history sample blended into the final color for fragments with significant active motion.
运动融合	运动碎片的混合系数。控制具有显著活动运动的片段的历史采样融合成最终颜色的百分比。
Sharpness	TAA can induce a slight loss of details in high frequency regions. Sharpening alleviates this issue.
锐利	在高频区域，TAA会引起轻微的细节丢失。锐化可以缓解这个问题。

Known issues and limitations 已知问题和限制

• Not supported on GLES2 platforms.

Requirements

• Motion vectors
• Depth texture
• Shader Model 3