MAYA / MEL _ flat shaded viewport

edit : Now in Maya 2015 there is an option for that in the viewport -> lighting -> use flat lighting.

I didn't find a simple way to display a flat shaded viewport. So here is a simple script to toggle the viewport with a flat shaded view, usefull to see silouhette when animating. This mel script create a global render layer with a surface shader material override, to change the flat color just modify the surface shader.

// TOGGLE FLAT - using render layer
global proc toggleFlat ()
{
 if (`editRenderLayerGlobals -q -currentRenderLayer` == "defaultRenderLayer")
 { 
  // Check if Render Layer FLat exists or create it
  if (`objExists "RL_FLAT"`)
  {
   editRenderLayerGlobals -currentRenderLayer RL_FLAT;
  }
  else
  {
   createRenderLayer -n "RL_FLAT" -number 1 -makeCurrent -global;

   // SHADER ///
   string $shadName = "SH_FLAT";
   // Check if Shader doesn't exists and create it
   if (!`objExists $shadName`)
   {
    $shader = `shadingNode -n $shadName -asShader surfaceShader`;
    setAttr ($shader + ".outColor") -type double3 0.7 0.7 0.7; 
   } 

   hookShaderOverride("RL_FLAT", "", "SH_FLAT");
   editRenderLayerGlobals -currentRenderLayer RL_FLAT;
  }
  headsUpMessage "FLAT ON";
 }
 else
 {
  editRenderLayerGlobals -currentRenderLayer defaultRenderLayer;
  headsUpMessage "FLAT OFF";
 }
 
}

toggleFlat ();