code: function (renderer, size) {
          renderer.saveClear();
          var viewport = renderer.viewport;
          var x = 0, y = 0;
          var width = size || viewport.width / 4;
          var height = width;
          if (this.softShadow === ShadowMapPass.VSM) {
              this._outputDepthPass.material.define('fragment', 'USE_VSM');
          }
          else {
              this._outputDepthPass.material.undefine('fragment', 'USE_VSM');
          }
          for (var name in this._textures) {
              var texture = this._textures[name];
              renderer.setViewport(x, y, width * texture.width / texture.height, height);
              this._outputDepthPass.setUniform('depthMap', texture);
              this._outputDepthPass.render(renderer);
              x += width * texture.width / texture.height;
          }
          renderer.setViewport(viewport);
          renderer.restoreClear();
      }
docs: Debug rendering of shadow textures
  @param  {clay.Renderer} renderer
  @param  {number} size
  @memberOf clay.prePass.ShadowMap.prototype