code: function( srcRgb, dstRgb, srcAlpha, dstAlpha ){
      this._dat[ 0|BLEND_FUNC_C_SRC ] = srcRgb;
      this._dat[ 0|BLEND_FUNC_C_DST ] = dstRgb;
      this._dat[ 0|BLEND_FUNC_A_SRC ] = srcAlpha;
      this._dat[ 0|BLEND_FUNC_A_DST ] = dstAlpha;
      this._set |= BLEND_FUNC_SET | BLEND_FUNC_A_SET;
      return this;
    }
docs: /*
  enums
  ZERO
  ONE
  SRC_COLOR
  ONE_MINUS_SRC_COLOR
  SRC_ALPHA
  ONE_MINUS_SRC_ALPHA
  DST_ALPHA
  ONE_MINUS_DST_ALPHA
  DST_COLOR
  ONE_MINUS_DST_COLOR
  SRC_ALPHA_SATURATE