Hi. Wanted to share a tip that gave me a bit of a boost when using KWin (KDE).
(The faster picture version is at the bottom).
KDE System Settings -> Window Behavior -> Window Rules
Click "New" for a new rule. Enter whatever you like for a description. Make "Window class (application)" set to "Exact Match" and "hl2_linux". Leave the rest alone here.
Then go to the "Apperances & Fixes" tab. I personally choose "No titlebar and frame" and "Force" it to "Yes". The more important one is "Block Compositing" and "Force" it to "Yes".
This causes KWin not to composite the window. It leaves the rest of your desktop unaffected. If you also remove the titlebar/border, you can use Alt+Drag (or Super+Drag depending on your system) to move the window around.
THIS WILL AFFECT ALL HL2_LINUX BASED GAMES. You may need to modify these rules to affect more games if you so desire.
Gallery of these steps: http://imgur.com/GnIi3LH,OQqRqcB,vdbNGxb,Xti6Rdq#0
Step 1: http://i.imgur.com/GnIi3LH.png
Step 2: http://i.imgur.com/OQqRqcB.png
Step 3: http://i.imgur.com/vdbNGxb.png
Step 4: http://i.imgur.com/Xti6Rdq.png