【Twinmotion】How “SSGI” works?


Although I heard that Twinmotion 2020 adopted new SSGI method, what’s that? So I validated it comparing with ver. 2019.

What is GI?

GI / Global Illumination creates a indirect illumination effect in the scene.

Take a look these photos. When I get a cup noodle closer to a wall, it becomes not only dark by shadow but also a little red. Also, When a slowpoke pokemon, it becomes a little pink. This is the indirect illumination!

GI can calculate and express this phenomenon, and can improve reality and quality of generated images.

How was it in Twinmotion 2019?

I made a test scene.

I changed color of floor, wall at the end, and sofa. I did not change lighting. Please compare to the image above. Due to the influence of indirect illumination, right wall and ceiling became a little red. More to say, around the end wall became slightly green.

I turned off sun light and on room lights. Then I became not to be able to see the influence of indirect light. In this way, indirect light is calculated based on only sun light in Twinmotion 2019. It seems not good for interior rendering.

How is it in Twinmotion 2020.1?

Let’s check it using the same scene. Please take a look and compare two images below. You can see that expression of indirect light became more realistic than ver. 2019. And also you can see the wall around sofa became a little blue by more accurate lighting culculation.

How about room lights? It may be difficult to understand, but please look closely and compare two images below. Wall and ceiling became just a little bit red, around sofa blue, around the end wall green. Like this, indirect light is calculated not only based on sun light but also room lights in Twinmotion 2020.1.

What is SS?

So, what is “SS / Screen Space” of SSGI? It means that GI is calculated only in the range of viewport. This mothod contributes to fast rendering in Twinmotion.

Take a look this example. I tried to pan up camera so floor became invisible in viewport, then …

Redness by indirect light has disappeared. Thus, you can understand that SSGI method works only with objects in viewport.

Extend range of influence of SSGI

You can set Refinement from Export > More in lower right of Image > Refinement so to extend range of influence of SSGI wider than viewport. When I set it high, even if the floor is invisible in viewport, red indirect light has expressed.

Refinement is named Max reflection in Twinmotion 2019. Please see a previous article below.

【Twinmotion】How “Max reflection (Refinement)” works?

The point

SSGI is Screen Space Grobal Illumination, means a method to culculate indirect light only with objects in viewport.

That’s all, thank you!