Qt Quick 3D - Custom Materials Example

 void MAIN()
 {
     vec2 size = vec2(textureSize(SCREEN_TEXTURE, 0));
     vec2 uv = FRAGCOORD.xy / size;

     vec2 d = vec2(1.0 / size.x, 1.0 / size.y);
     vec4 diff = texture(SCREEN_TEXTURE, uv + d) - texture(SCREEN_TEXTURE, uv - d);
     float c = (diff.x + diff.y + diff.z) + 0.5;

     float alpha = 1.0;
     if (uKeepAlpha)
         alpha = texture(SCREEN_TEXTURE, uv).a;

     BASE_COLOR = vec4(vec3(c), alpha);
 }