Pvrtc compressed ktx textures displaying incorrectly on iOS

[br-matt]

Hello, been trying to use device specific textures for performance and memory reasons. It’s going well on other platforms except iOS. Here is what this PG ( https://www.babylonjs-playground.com/#5I4TDH#14 ) looks like on iOS.

( pvrtc ktx on left, ktx2 on right )

This is what the diffuse maps look like in PVRTexTool
(pvrtc ktx)

(ktx2)

Any help much appreciated : )

[Deltakosh]

I think @bghgary was investigating something similar recently

[bghgary]

What version of iOS are you running?

[br-matt]

Its on 15.4

[bghgary]

It looks like only specific PVRTC formats are supported on the web.

WebGL WEBGL_compressed_texture_pvrtc Extension Specification (khronos.org)

    const GLenum COMPRESSED_RGB_PVRTC_4BPPV1_IMG      = 0x8C00;
    const GLenum COMPRESSED_RGB_PVRTC_2BPPV1_IMG      = 0x8C01;
    const GLenum COMPRESSED_RGBA_PVRTC_4BPPV1_IMG     = 0x8C02;
    const GLenum COMPRESSED_RGBA_PVRTC_2BPPV1_IMG     = 0x8C03;

The format in the ktx is 35415 (0x8A57) which apparently is GL_COMPRESSED_SRGB_ALPHA_PVRTC_4BPPV1_EXT.

[br-matt]

Thank you @bghgary ! I guess sRGB not supported. ASTC seems to work fine instead as a workaround on device