Issues with HALF_FLOAT on Mali GPUs

I have reports from my users about issues with rendering of half-floats data on certain devices with Mali GPUs (Huawei Honor 9 and Samsung Galaxy S10+ w/ Mali G71 and G76 respectively).

It results in garbled rendering on these devices while works correctly on Adreno and PowerVR GPUs.

I've double checked code and it seems to be correct:

...
     if (model.hasHalfFloats()) {
         GLES20.glVertexAttribPointer(shaderOutline.getRm_Vertex(), 3, GLES20.GL_FLOAT, false, 18, 0);
         GLES20.glVertexAttribPointer(shaderOutline.getRm_Normal(), 3, getGL_HALF_FLOAT(), false, 18, 12);
     } else {
         GLES20.glVertexAttribPointer(shaderOutline.getRm_Vertex(), 3, GLES20.GL_FLOAT, false, 24, 0);
         GLES20.glVertexAttribPointer(shaderOutline.getRm_Normal(), 3, GLES20.GL_FLOAT, false, 24, 12);
     }
...

/**
 * Returns either OES extension for GL 16-bit floats (if used in ES 2.0) or ES 3.0 constant.
 */
protected int getGL_HALF_FLOAT() {
    if(isES3()) {
        return GLES30.GL_HALF_FLOAT;
    } else {
        return GL_HALF_FLOAT_OES;
    }
}

Code seems to correctly detect OpenGL ES 3 and use GLES30.GL_HALF_FLOAT value in getGL_HALF_FLOAT().

Sample shader code:

    vertexShaderCode = "attribute vec4 rm_Vertex;\r\n" + 
            "attribute mediump vec3 rm_Normal;\r\n" +
            "uniform mat4 view_proj_matrix;\r\n" + 
            "uniform float uThickness1;\r\n" + 
            "void main( void )\r\n" + 
            "{\r\n" + 
            "   vec4 pos = vec4(rm_Vertex.xyz, 1.0);\r\n" + 
            "   float dist = (view_proj_matrix * pos).w;\r\n" + 
            "   vec4 normal = vec4(rm_Normal, 0.0);\r\n" + 
            "   pos += normal * uThickness1 * dist;\r\n" + 
            "   gl_Position = view_proj_matrix * pos;\r\n" + 
            "}";

    fragmentShaderCode = "precision mediump float;\r\n" + 
            "uniform vec4 uColor;\r\n" + 
            "void main( void )\r\n" + 
            "{\r\n" + 
            "    gl_FragColor = uColor;\r\n" + 
            "}";

Solution

I think you have an alignment problem. From this snippet (and your vertex shader):

GLES20.glVertexAttribPointer(shaderOutline.getRm_Normal(), 3, getGL_HALF_FLOAT(), false, 18, 12);

I can infer that you're attempting a vertex structure like so:

float fPos[3];
half fNormal[3];

You have come up with a vertex stride of 18 which has presumably been arrived at by adding up the individual sizes of the elements (3*sizeof(float))+(3*sizeof(half)) = 12 + 6 = 18.

However, the stride should be 20 because otherwise your vertices are misaligned. The 4-byte floats must start on a 4-byte boundary, but that is not the case.

From the GLES3 spec:

Clients must align data elements consistently with the requirements of the client platform, with an additional base-level requirement that an offset within a buffer to a datum comprising N basic machine units be a multiple of N