OpenGL: optimizing render of quad particles

Question

I'm rendering particles in a 2D game. Each particle is a quad (2 triangles). How can I make the drawing the fastest possible? All the particles has the same texture, I'm only changing it's positions.

Now I'm using a call to glVertexPointer and glDrawArrays for each particle. So I'm sending 4 vertices each time to the GPU.

Is there any other approach that could be faster?

I'm using OpenGL ES 1.1 (iPhone)

Thanks!

Answer 1

Every draw call you make (glDrawArrays) is expensive. Doing this once per particle is DEFINITELY way too often. All your particles can be drawn with a single draw call; just set up a big array of all the triangle verts and another big array with the texture coords, and call glVertexPointer/glDrawArrays once-- that's the power of glVertexPointer: arbitrary geometry of the same type in one call. :)

For what you're doing, you should also look into point sprites (GL_POINTS), which also function as tiny textured quads. They're 2D only, so you can't map your texture into the Z axis, but if your particles are just 2D quads of the same texture over and over, point sprites will likely do exactly what you want.

Answer 2

There's a way to do that all in one draw routine. I THINK it's by adding an extra vertex after each quad, which is the same as the previous vertex, but I could be wrong.

EDIT: After looking into it a bit, it looks like you need two in between; essentially one after, and one before. It does add up to quite a few extra vertexes, but I know from experience that it makes a HUGE positive difference on the iPhone to do it all in one draw operation (we were drawing text from a texture, so essentially the same thing).

EDIT2: Also note, I'm referring to using GL_TRIANGLE_STRIP - if you were using GL_TRIANGLES instead, you wouldn't need the extra vertices... except, then you'd be doing the same amount extra anyway, due to repeating 2 for each second triangle.