title: GameMaker Studio, GLSL ES Shader, different results on Android
body: <p>I try to implement a fullscreen GLSL ES shader in my GameMaker Studio project. However, I get different results on almost every device I test. I made a small test project to showcase the problem.</p>
  
  <p>Vertex Shader:</p>
  
  <pre><code>attribute vec3 in_Position;                  // (x,y,z)
  //attribute vec3 in_Normal;                  // (x,y,z)     unused in this shader.
  attribute vec4 in_Colour;                    // (r,g,b,a)
  attribute vec2 in_TextureCoord;              // (u,v)
  
  varying vec2 v_vTexcoord;
  varying vec4 v_vColour;
  
  void main()
  {
      vec4 object_space_pos = vec4( in_Position.x, in_Position.y, in_Position.z, 1.0);
      gl_Position = gm_Matrices[MATRIX_WORLD_VIEW_PROJECTION] * object_space_pos;
  
      v_vColour = in_Colour;
      v_vTexcoord = in_TextureCoord;
  }
  </code></pre>
  
  <p>Fragment shader:</p>
  
  <pre><code>varying vec2 v_vTexcoord;
  varying vec4 v_vColour;
  
  void main()
  {
      if(v_vTexcoord.x &gt; 0.5)
      {
          gl_FragColor = vec4(0,1,0,1);
      }
      else if(v_vTexcoord.y &gt; 0.5)
      {
          gl_FragColor = vec4(0,0,1,1);
      }
      else
      {
          gl_FragColor = v_vColour * texture2D( gm_BaseTexture, v_vTexcoord );
      }
  }
  </code></pre>
  
  <p>And these are the results:<br>
  <a href="https://dl.dropboxusercontent.com/u/14513191/shader_problem.jpg" rel="nofollow">https://dl.dropboxusercontent.com/u/14513191/shader_problem.jpg</a></p>
  
  <p>This is how it should look on <strong>PC</strong> / 1920x1080<br>
  Samsung <strong>Galaxy Alpha</strong> / 1280x720<br>
  <strong>PadFone Infinity</strong> / 1920x1080</p>
  
  <p>Has anyone an idea what's going on here?</p>