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Directional Light with Default Material have large brightness differences between Mobile and Desktop

I have a very simple scene setup. A plane with a default material applied, with the plane facing the camera and a directional light aimed down towards the plane from the upper right corner. When I view the results in both Shader Model 5 vs Mobile Preview ( both High End and Low End Mobile ) I see a large lighting difference between Shader Model 5 and Mobile Preview. I verified that I am not making use of Auto Exposure and have it set to 0. I have no texture inputs, and the material is at it's default settings ( except for full precision for mobile, though this made no difference ). In my Project Settings I made sure to turn on Mobile HDR as well.

Visually this seems to be a difference in shading, seemingly in the specular response ( I zeroed out the specular and used a black color input to the base color and both Shader Model 5 and Mobile Preview gave the same result ( images below ) ). I am not making use of shadows currently ( they are on for the light, but turning them off also gave the same exact result ). Setting my light from Moveable to Stationary made no difference, and using Static isn't an option for this game.

I have looked through many questions on AnswerHub regarding visual differences between Mobile and Desktop, but nothing has so far helped me. I am really hoping I am missing something.

Shader Model 5 alt text

High End Mobile alt text

Low End Mobile alt text

Material Properties alt text alt text

Product Version: UE 4.15
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asked Mar 17 '17 at 07:34 PM in Rendering

avatar image

Institute Games
76 2 6 12

avatar image Institute Games Mar 17 '17 at 08:08 PM

Continued as I couldn't include enough images in the first part:

Directional Light Properties alt text alt text alt text


avatar image Institute Games Mar 17 '17 at 08:31 PM

I am surprised to see differences in the Detail Lighting, Lighting Only, and Unlit views between Shader Model 5 and High End Mobile. There shouldn't be visual changes especially in Unlit unless the default values are different between Shader Model 5 and Mobile shaders, though I doubt this is the case as I piped in a black color into the material and I still got the same results. Is it possible that sRGB isn't handled the same between Shader Model 5 and Mobile shaders?

Shader Model 5 Detail Lighting alt text

High End Mobile Detail Lighting alt text

avatar image Institute Games Mar 20 '17 at 11:01 PM

Unfortunately, as the Buffer Visualizer doesn't seem to work when in Mobile Preview mode, I couldn't see what default values looked like for Roughness or Specular like I could using Shader Model 5.

Shader Model 5 Lighting Only alt text

High End Mobile Lighting Only alt text

Shader Model 5 Unlit alt text

High End Mobile Unlit alt text

avatar image Institute Games Mar 20 '17 at 11:03 PM

I Zeroed out the Specular of the Material, and the results were the same as I show below. It seems that the specular handling between Shader Model 5 and Mobile is at fault. I am unsure why the difference is so large, especially when not using any texture inputs. Simply put, with a ZEROED Specular, I shouldn't see ANY specular response in the shader, yet I am in the Mobile shader. I am a bit of a loss on how to proceed.

Shader Model 5 Specular Zeroed alt text

High End Mobile Specular Zeroed alt text

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