Cubemap quality bug in IE11

[jinwoobot]

This article what i wrote on forum
https://forum.playcanvas.com/t/ie11-webgl1-cubemap-is-strange-engine/11683/3

Description

I’ve just tried setting on cubemap (engine code).
It works fine on chrome and Edge browsers but it doesn’t work as my expectation in IE 11.

• URL to a simple, reproducible test case.
  https://github.com/velbi/cubemap-test

• Screenshots

• Edge
  

• Chrome
  

• Internet Explorer 11
  

Steps to Reproduce

1. Clone https://github.com/velbi/cubemap-test
2. Add some server (I just use yarn add live-server)

[willeastcott]

I believe this is because your app has app.scene.skyboxMip set to 0. In this case, the skybox is rendered using the PNG cubemap faces (whereas if app.scene.skyboxMip is set to 1 or more, it uses the DDS image data). IE11 has a bug where it will premultiply the RGB data by A and then it is divided away when the texture is used and this causes precision loss and hence the banding. Hey, @slimbuck - did I get that right? Is it worth keeping this issue open (since it's not technically a PlayCanvas bug). Or do you hope we can devise a workaround to this where we no longer rely on PNG format for holding RGBM data?

[slimbuck]

That's exactly right @willeastcott. I think it's worth keeping this ticket around because it this this also still a problem on iOS and we should find a workaround.

[willeastcott]

The new RGBP format (introduced by @slimbuck) should resolve this. Also, the iOS issue @slimbuck references above is now resolved (see #1930). Plus, with the vanishingly small userbase of IE11 these days, I'm closing this.