code: function (shader) {
              if (this.activeShader !== shader) {
                  this.flush();
                  this.activeShader = shader;
                  this.activeShader.bind();
                  this.activeShader.uniforms.uProjectionMatrix = this.projectionMatrix.val;
              }
          }
docs: Select the shader to use for compositing
  @name useShader
  @see me.GLShader
  @memberOf me.WebGLRenderer.Compositor
  @function
  @param {me.GLShader} shader a reference to a GLShader instance