Upsample

Unreal升采样策略

有两种策略

Prior to Unreal Engine 4 (UE4) version 4.19, you only had to change the screen percentage, but it has now been split into two types of scaling during the rendering pipeline: Primary and Secondary Spatial Upscaling.

• Primary Spatial Upscaling is the same screen percentage that has been used previously. It is based on the idea of rendering a frame at a lower resolution and then upscaling it before the user interface (UI) is drawn.

• Secondary Spatial Upscaling does a second and final spatial upscale pass, independently of the Primary upscaling pass.

Primary Spatial Upscaling

整体缩小比例渲染，在绘制UI之前upscale，，一般混在最后一个后期pass里一起做

The tonemapper integrates a simple bilinear color space spatial upscale that can be used for performance reasons when enabled using a value of 1. However, if a Post Process Material is inserted after the tonemapper, the tonemapper won’t do the upscale. It will fall back to using the primary spatial upscale as if it were disabled.

升采样质量级别

Primary Spatial Upscaling 的一种：TAA Upsample也叫 Temporal Upsampling

In addition to Primary Spatial Upscale, a second upscaling technique is also supported for the primary screen percentage: Temporal Upsample. Instead of performing temporal integration with the Temporal Anti-Aliasing (TAA) and then doing a primary spatial upscale, both happen at the same time in the Temporal Anti-Aliasing Upsample (TAAU) shader. It also allows them to converge to sharper images than what a spatial-only upscale could provide but comes at a higher cost since a larger number of post processes run at a higher resolution. It also allows for primary screen percentage changes to be hidden by dynamic resolution allowing it change more often to match the GPU budget as closely as possible.

As the primary screen percentage decreases, the convergence to a clean full-resolution output changes. Therefore, some existing TAA artifacts would be more noticeable. For example, aliasing can become an issue for very thin geometry increasing the probability to miss this geometric detail as the primary screen percentage is lowering.

Secondary Spatial Upscale

TAA升采样一次，最后一个pass再升采样一次

弄到Unity试了一下果然36Tap高斯的结果最好

Unity中动态分辨率升采样策略

https://forum.unity.com/threads/using-dynamic-resolution-change-with-screen-setresolution-destroys-my-default.510801/

Don’t use SetResolution to dynamically change the resolution for performance. Instead have your camera render to a render texture which you Blit() to the framebuffer (Blit to a null destination). Get a temporary render target each frame and adjust its size depending on the current framerate. Usually this is done for the “game” camera only and the UI camera is left at full res. This has been the standard practice for console games since the original Xbox era.

Game相机的CameraTarget用低分辨率(可以根据帧率动态改变分辨率)，在UICamera渲染之前用Upscample升到全分辨率

void OnPreCull ()
  {
      if (Globals.Configdata.DynamicFPS) {
          if (Globals.Configdata.resolutionWidth == 0 || Globals.Configdata.resolutionHeight == 0) {
              Globals.Configdata.resolutionWidth = Screen.currentResolution.width;
              Globals.Configdata.resolutionHeight = Screen.currentResolution.height;
          }
          cameraTarget = RenderTexture.GetTemporary (Globals.Configdata.resolutionWidth, Globals.Configdata.resolutionHeight, 24);
          Camera.main.targetTexture = cameraTarget;
          // this ensures that w/e the camera sees is rendered to the above RT
      }
  }

camera render to a render texture which you Blit() to the framebuffer (Blit to a null destination).

Graphics.Blit (cameraTarget, null as RenderTexture);

Blit null为画到frameBuffer上，，测试表明，PC上Deferred管线下，第二个相机是从FB中取参数的，必须画到frameBuffer上，，iphone

升采样实现

https://www.cs.toronto.edu/~guerzhoy/320/lec/upsampling.pdf

基本思想就是采样周围的点按照一定比例插值混合

不同类型升采样插值的结果

也可以用于resampling

双线性插值算法

参考:

https://docs.unrealengine.com/en-us/Engine/Rendering/ScreenPercentage

https://clouard.users.greyc.fr/Pantheon/experiments/rescaling/index-en.html

https://gis.stackexchange.com/questions/10931/what-is-lanczos-resampling-useful-for-in-a-spatial-context