Sunday, August 24, 2014

[Unreal Engine 4] Improving Screen Space Reflections

If you ever felt the need to adjust or improve the built-in screen space reflections of UE4 take a look at the ScreenSpaceReflections.usf shader file.
It's located in this directory: \Unreal Engine\4.x\Engine\Shaders\

In the SSR shader file search for this part of the code. The line number varies a bit with each engine version, but it should be somewhere around 340-350.
#if SSR_QUALITY == 1
const int NumSteps = 8;
const int NumRays = 1;
#elif SSR_QUALITY == 2
const int NumSteps = 16;
const int NumRays = 1;
#elif SSR_QUALITY == 3
const int NumSteps = 8;
const int NumRays = 4;
#else // SSR_QUALITY == 4
const int NumSteps = 12;
const int NumRays = 12;
There are 3 quality levels with 2 parameters which define the quality of reflections.

NumSteps - Number of steps. This defines the accuracy of reflections and causes a reasonable performance impact.
For any value above 32 you will hardly notice a difference
NumRays - Number of rays. Using more rays takes away the noise of reflections but is rather expensive.

The default settings are a bit strange since the number of steps drops from 16 back to 8 at quality level 3. My recommendation would be to set NumSteps to 16 for high quality. This comes at a little performance impact. You might also lower NumRays by 1 at the same time to gain back the lost FPS.

Here's a set of screenshots to demonstrate various value combinations as well as their impact on performance.

NumSteps=8 / NumRays=1

NumSteps=16 / NumRays=1

NumSteps=16 / NumRays=2

NumSteps=8 / NumRays=4

NumSteps=16 / NumRays=4

NumSteps=16 / NumRays=8

NumSteps=32 / NumRays=4

NumSteps=32 / NumRays=8

NumSteps=32 / NumRays=32


  1. Hey Oliver, thanks for posting this. Is it possible to get access to those variables via an ini file or in the console in the editor? Or is it only through the shader file...


    1. No, this is not possible. You can only change the SSR quality level via console command or in the post process volume settings, so that's 4 presets to test per run.

  2. I just want to say thank you!