Webgl Fustrum View


When I Render 5 boxes in webgl with 1 texture all of them, the app runs at 60 fps, nice.
But when I render 70 boxes the performance dicrease to ~40fps but in the view volumes
are still 5.

I have debugged the app and all 70 boxes are using per fragment shaders when there are no need because 65 of them are out of frustum. I thought that gl.viewport declaration clipped out of view polygons but not.

I would like to know if fustrum culling the technique to avoid this? How can I activate fustrum culling? Is there any webgl command or I have to do it manually?

Thanks in advance,