title: Button beyond an background Image
body: <p>i think i don't find the correct word for the title so i will try to explain correctly.</p>
  
  <p>So i have this image for a backround of my Layout :
  <a href="http://imageshack.us/photo/my-images/607/fond1g.png/" rel="nofollow">http://imageshack.us/photo/my-images/607/fond1g.png/</a></p>
  
  <p>And i would like to the button fit in it correctly.</p>
  
  <p>Because there are some transparancy on the left and on the right.
  So the button are beyond the sheet.</p>
  
  <p>Is there something for say "Hey this is transparency and i don't want anything in it" ?
  Or "Hey this is where (the sheet) i want to put everything ?</p>
  
  <p>I tried to put another LinearLayout but i don't know how to give the good width.</p>
  
  <p>Thanks</p>