Question

our live wallpaper doesn’t work properly on Motorola Atrix phone. It has a stock ROM w/ Android 2.3.
It looks like discard command of fragment shader doesn’t work resulting image without transparent parts.
The problem doesn’t appear on Desire S w/ Android 2.3, Mototola Droid w/ CM9, ASUS Transformer w/ 4.0, Samsung Galaxy Note w/ 4.0. So the problem seems to be very specific to Motorola Atrix phone.
We use ETC1 compressed textures so alpha channel is passed to shader via separate texture sampler – sTexture is used for main diffuse texture and sAlpha has black-and-white alpha channel.

Here is code for fragment and vertex shaders:

private final String mVertexShader = "uniform highp mat4 uMVPMatrix;\n" +
        "attribute highp vec4 aPosition;\n" +
        "attribute highp vec2 aTextureCoord;\n" +
        "varying mediump vec2 vTextureCoord;\n" +
        "void main() {\n" +
        "  gl_Position = uMVPMatrix * aPosition;\n" +
        "  vTextureCoord = aTextureCoord;\n" +
        "}\n";

private final String mAlphaFragmentShader = "precision mediump float;\n" +
        "varying mediump vec2 vTextureCoord;\n" +
        "uniform sampler2D sTexture;\n" +
        "uniform sampler2D sAlpha;\n" +
        "void main() {\n" +
        " vec4 base = texture2D(sTexture, vTextureCoord);\n" +
        " gl_FragColor = base;\n" +
        " if(texture2D(sAlpha, vTextureCoord).r < 0.5){ discard; }\n" +
        "}"; 

Answer 1

OK so I’ve fixed this. Many thanks to @Tim for willing to run test apps on device and providing me screenshots.
I’ve modified fragment shader the following way:

private final String mAlphaFragmentShader = "precision mediump float;\n" +
        "varying mediump vec2 vTextureCoord;\n" +
        "uniform sampler2D sTexture;\n" +
        "uniform sampler2D sAlpha;\n" +
        "void main() {\n" +
        " vec4 base = texture2D(sTexture, vTextureCoord);\n" +
        " vec4 mask = texture2D(sAlpha, vTextureCoord);\n" +
        " gl_FragColor = base;\n" +
        " if(mask.g < 0.5){ discard; }\n" +
        "}";

It seems that Motorola Atrix OpenGL drivers treat compressed textures in wrong way and sample R channel as A channel which is always 1.0 in case of ETC1 compressed textures. It looks like internal format of texture is treated as ARGB instead of RGBA. Since my mask texture is black-and-white I can fetch any other colour. Green works just fine.