I am trying to create a glowing star. For this purpose, I loaded a texture from a bitmap file and mapped that texture on to a square quad. And then I called glBlendFunc(GL_SRC_ALPHA, GL_ONE). For the most of the stars (when they overlap) there is a great transparancy that I wanted. But sometimes, for some reason, the square of quad suddenly appears. But this is not always happening. How can I prevent the square apperance.