Mobile Lighting Artefacts / Device Rendering Issues
Note: This full project including source code has been sent via PM to Tim Hobson, in the hope that these issues can be looked into more directly. Please ask him for the files if you need them, they need to remain internal to Epic and kept private :)
I am experiencing some severe lighting and rendering issues on Mobile that have persisted since at least 4.9 and still occur in 4.10. None of the issue here occur when running the game in PIE or in a packaged Windows game - only Mobile or Mobile Preview mode.
The game relies on Dynamic Lighting from a single directional light that acts as the sun, with very mild ambient lighting from a skylight. The skylight itself seems to be behaving as expected, but the dynamic light is causing a tonne of rendering artefacts. The devices I'm testing on are an nVidia Shield and a Sony Xperia Z1 Compact (DXT and ATC respectively). I've been told that the phone uses a Snapdragon 800 GPU. The game has Mobile HDR enabled, and is using the standard ES2 renderer. I have tried ES3.1 AEP previously way back in 4.8, but the issues still persisted there.
Some of these issues are not visislbe in the Mobile Previewer in Editor and only occur when the game is deployed to the device. I have PM'd Tim Hobson with a private copy of the game and it's assets, in the hope that the issue can be resolved or at least confirmed on Epic's end.
The first issue is harsh shadowing artefacts from the Dynamic Light. I am fairly certain I have the shadow cascading setup correctly, and what's confusing is that this only seems to affect the Satellite in Mobile Preview, but affects all objects when deployed to the device. Any surfaces that are even slightly facing away from the sun are shadowed incredibly harshly, and there is no soft shadowing.
The first image below shows the game running in the mobile previewer in the editor. Notice the harsh shadow artifacts on the underside of the solar panels. The shadowed faces have normals that aren't perfectly flat, but they still shouldn't receive shadows as harsh as this. Non-mobile preview doesn't produce these artifacts. You can also see that the Earth object has a regular soft shadow, and does not have any harsh blending in Mobile Previewer.
When deployed to the device however, not only do the artifacts on the Satellite persist, the Earth also gets shadowed incredibly harshly:
Additionally, you can also see that the (very simple) Atmosphere shader of the Earth also doesn't draw correctly on the mobile device, even though it brings up no warnings or rendering errors in the Mobile Previewer. This is an incredibly simple material, the graph of which is posted below. If you have the source files, it's in Content->Earth->Materials->Mat_AtmosBlue. What would cause it to render completely solid? It's as if the Fresnel never get's calculated properly.
The final issue, is that the sun disk disappears from the Universe Sky-dome. This sky-dome uses the same method as the engines BP_SkySphere Blueprint to draw the disc, except that the light vector is already preset in the material. On mobile however, the sun disc disappears, as if the light has been removed entirely. Again, the material editor gives me no warnings about incompatible operations or nodes on ES2.
As you can see there are some very significant differences between the deployed results and those in the Mobile previewer, which makes this difficult if not impossible for me to fix - especially the Materials. If somebody with more knowledge of the mobile renderer could take a look at this (I've sent the full project inc. source code to Tim Hobson), I would be eternally grateful. If I'm trying to achieve the impossible, It would be nice to know sooner rather than later so I can think about workarounds :)
There does appear to be an issue we are looking into about precision on certain levels of Android devices. We are tracking this issue as UE-25532. I have updated teh report to include your additional information and links to this Answehub and your last forum post listed above. As always we will try to keep you informed here as we get new updates.
answered Jan 21 '16 at 05:31 PM
Lovecraft_K ♦♦ STAFF
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