setDepthMask( depthMask ) {

		if ( this.currentDepthMask !== depthMask ) {

			this.gl.depthMask( depthMask );
			this.currentDepthMask = depthMask;

		}

	}
Specifies whether depth values can be written when rendering
into a framebuffer or not.

This method caches the state so `gl.depthMask()` is only
called when necessary.

@param {boolean} depthMask - The depth mask.