From Valve Developer Community
- Create a brush where you want the glass to be, using the nodraw texture. Like real glass, it should be very thin (No more than 3 units thick under normal circumstances).
- Apply a nice-looking glass texture to one face (not on both sides). Make sure you use
glass/glasswindowbreak070a. Don’t use
glass/glasswindowbreak070b. ALL OTHER FACES MUST BE
tools/toolsnodraw! IF NOT, IT WILL NOT BE SPAWNED IN-GAME!
- Select the brush and click the "Entity" button in the object toolbar. Choose func_breakable_surf in the drop-down list. (If you want the glass to completely shatter all at once, choose func_breakable instead.)
- Go to the Material Type keyvalue and select Glass.
- Optional: Add an env_cubemap to the surface of the glass texture.
You can apply your texture to just one side of the brush entity by opening the Hammer Face Edit Dialog, ensuring the Mode is set to Select or Lift + Select, and clicking once in the 3D view on the face you want to apply the texture to. Then, select a material with either the drop down box or the browse button, and click apply.
func_breakable Has the effect of breaking all the glass (see picture)
func_breakable_surf Has the effect of partially breaking the glass (see picture)