Why one sprite need two drawcalls?

[Dalek]

Hi. I am using the sprite for some effect when I found that each sprite has two drawcalls. What is the perpose of the code below?

            engine.setDepthFunctionToLessOrEqual();
            effect.setBool("alphaTest", true);
            engine.setColorWrite(false);
            engine.drawElementsType(Material.TriangleFillMode, 0, max * 6);
            engine.setColorWrite(true);
            effect.setBool("alphaTest", false);

            engine.setAlphaMode(Engine.ALPHA_COMBINE);
            engine.drawElementsType(Material.TriangleFillMode, 0, max * 6);
            engine.setAlphaMode(Engine.ALPHA_DISABLE);

Why "engine.drawElementsType" is called twice?

[Sebavan]

yes, it all makes sense as we first fill only the depth buffer and in a second time the color one to help with ordering.