glTF 2.0 model lose light on Andoird

[alx696]

• Ubuntu 18.04 Chrome 71.0.3578.80
• Android 8.0 Chrome 70.0.3538.80 Samsung S8
• Cesium 1.52

Problem:

1. Aplha lost;
2. Model dark on Android;
3. Below is whiter than above;
4. White Color yellowing(1.43 right, 1.45 little yellowing, 1.52 much yellowing).

Blender file:
https://github.com/alx696/share/raw/master/gltf/box.zip

glTF2.0 file:
https://github.com/alx696/share/raw/master/gltf/box.gltf

Disable shadows of gltf not work:

      let model = viewer.scene.primitives.add(Cesium.Model.fromGltf({
        url: `gltf/box.gltf`,
        modelMatrix: transforms,
        shadows: Cesium.ShadowMode.DISABLED,
        minimumPixelSize: 128,
        maximumScale: 20000
      }));

Android WebGL Report: #6622 (comment)

Model render:

Ubuntu 18.04 Chrome 71.0.3578.80:

Android 8.0 Chrome 70.0.3538.80 Samsung S8:

Just now, i found a old phone(GPU Mali-T720). The model show well. But new phones are dark.

Old Phone WebGL Report:

• WebGL1: https://github.com/alx696/share/blob/master/image/20181212_112615.jpg
• WebGL2: https://github.com/alx696/share/blob/master/image/20181212_112632.jpg

[alx696]

Other phone same problem:

Phone Info: https://www.gsmarena.com/xiaomi_mi_4c-7512.php

https://github.com/alx696/share/raw/master/image/gltf-box%E6%89%8B%E6%9C%BA%E4%B8%8A%E6%95%88%E6%9E%9C-%E5%B0%8F%E7%B1%B3.png

[likangning93]

I'm actually able to get the same effect on Adreno 308:

@alx696 thanks for the model, for anyone else testing here's the scene on cesiumjs.

[alx696]

Cesium 1.43 looks better, But still dark on no sun area:

PC:
https://github.com/alx696/share/blob/master/image/glTF%E5%A4%AA%E9%98%B3%E5%85%89%E9%98%B4%E5%BD%B11-%E7%94%B5%E8%84%91.png

https://github.com/alx696/share/blob/master/image/glTF%E5%A4%AA%E9%98%B3%E5%85%89%E9%98%B4%E5%BD%B12-%E7%94%B5%E8%84%91.png

Android:
https://github.com/alx696/share/blob/master/image/glTF%E5%A4%AA%E9%98%B3%E5%85%89%E9%98%B4%E5%BD%B11-%E6%89%8B%E6%9C%BA.jpg

https://github.com/alx696/share/blob/master/image/glTF%E5%A4%AA%E9%98%B3%E5%85%89%E9%98%B4%E5%BD%B12-%E6%89%8B%E6%9C%BA.jpg

[OmarShehata]

This should be fixed with #7944, and will be out with CesiumJS 1.59 coming out next week.