I want to blend two png images to create ground texture, following this tutorial http://wiki.ogre3d.org/Materials#Simple_texture_transition. I want to take the dirt.png and grass.png and blend it using the terraing.png blend image.

dirt.png

grass.png

terrain.png

I'm using following material script

material GrassGround/Blend
 {
    technique
    {
       pass
       {

          scene_blend alpha_blend

          texture_unit
          {
            texture dirt.png
            scale 0.01 0.01
          }

          texture_unit
          {
             texture terrain.png
             colour_op alpha_blend
          }

          texture_unit
          {
            texture grass.png 
            scale 0.01 0.01
            colour_op_ex blend_current_alpha src_texture src_current
          }
       }
    }
 }

But the resulting texture is only the grass texture.

I have also noticed a note in the ogre documentation that says:

colour_op

Note
    Only has an effect with the fixed-function pipeline or the RTSS: Run Time Shader System

Might that have anything to do with the fact, that the script doesn't work as I expect it to? I don't know what fixed-function pipeline or RTSS is. Can I switch it on or something? Might there be another problem?