Android Texture Artifacts

[TokisanGames]

m4gr3d ran terrain3d on android (samsung galaxy tab) and it works fine, except the shader looks like it has terrible floating point precision.

https://chat.godotengine.org/channel/android?msg=Xo95Qcs52bv3BAF2X

Screen_Recording_20231116_153742_Terrain3D.mp4

terrain_3d_demo_godot_android_editor.mp4

@Calinou suggested

I guess you need a highp annotation in some places

[Calinou]

Be careful to only use highp where absolutely needed, or performance will suffer.

My guess is that you need to use highp for UV coordinates here.

[TokisanGames]

@Calinou according to the docs highp is the default (on desktop presumably) so adding it shouldn't affect performance at all, right?

According to the image above, it looks like maybe lowp is the default on android/mobile renderer? So changing the UV to highp or even mediump will only affect android performance.

@m4gr3d, did you use the mobile renderer? Do you want to help troubleshoot this? If you enable custom shader in the storage resource, it will give you an editable one and you could experiment with adding mediump and highp around the shader.

[Calinou]

According to the image above, it looks like maybe lowp is the default on android/mobile renderer? So changing the UV to highp or even mediump will only affect android performance.

Yes, this is exactly what's happening 🙂

I think desktop GPUs tend to ignore precision hints anyway. The hints are mostly needed for mobile GPUs. (This is not about the rendering method, but about the graphics driver.)

[m4gr3d]

@m4gr3d, did you use the mobile renderer? Do you want to help troubleshoot this? If you enable custom shader in the storage resource, it will give you an editable one and you could experiment with adding mediump and highp around the shader.

Yes, I used the mobile vulkan renderer. I can try modifying the custom shader to see if that improves things.
I'll also post a draft PR with a custom build of the Android editor with the functionality enabled to allow others to test as well.

[m4gr3d]

@TokisanGames I played around with adding highp to the custom shader, but that had no effect on the rendering artifacts.

[TokisanGames]

Ok. Another possibility is that DDS textures aren't supposed to work on android anyway. Since Godot doesn't import them, it isn't converting them. Perhaps the android sdk or OS is converting them poorly? What if PNG textures are used, imported with ETC2 enabled in the project settings and with vram compressed? That way Godot will convert to proper etc2 files. However this line might need to be changed to allow Image::FORMAT_ETC2_R11S (hopefully) and/or Image::FORMAT_RGBA8 (hopefully not).

[TokisanGames]

It was reported that the cause of this issue has been found:

https://discord.com/channels/691957978680786944/1065519581013229578/1192757400315363398

[m4gr3d]

It was reported that the cause of this issue has been found:

https://discord.com/channels/691957978680786944/1065519581013229578/1192757400315363398

I'm unable to access the discord link; can you paste the cause of the issue here?

[Calinou]

Perhaps the android sdk or OS is converting them poorly?

The Android OS/SDK does nothing special to DDS textures. These need to be decoded on the CPU by Godot (or transcoded to a compatible VRAM-compressed format) if S3TC support isn't available on the hardware.

We could choose to perform this automatically on unsupported formats, but it comes with a significant impact on memory usage (if decoding to lossless) or quality and binary size (if transcoding to ETC2). Both choices will impact loading times negatively too, but transcoding will be particularly bad on this aspect.

(Note: This assumes we are talking about an exported project or runtime DDS loading here, with no existing ETC2 textures available.)

[TokisanGames]

I think this artifact is due to or related to using DDS files since android doesn't have wide support for them. I think that using PNGs which get converted to etc2 would be fine, but I haven't confirmed that. I have replaced the demo textures with PNG so it can be a mobile demo as well.

@lfxu reported this, which I have not tested or implemented myself yet:

I found the cause, precision issue.


Of course this is incorrect, probably having a offset, but you get the idea.
interpolation of large UV value produce poor precision results at fragment shader input.

These are all the changes I did.
I think you want to check other varyings too.

[TokisanGames]

Fixed in #296. We can use more android testers to confirm. I heard everything with android should be working now. The github builds include android arm 32 & 64.