OpenGL ES Graphics issue when not calling glClear()

I'm working on an i开发者_JAVA技巧Pad app that has a few thousand particles that the user can manipulate with touches. To produce interesting designs, I want to make it so that when a particle is drawn in a location, that drawing is not cleared on the next frame. This creates a sort of "trails" effect. At the moment I'm doing this by when "trails" is turned on, glClear() is not called each frame, so drawing from each frame is added to the drawing of the previous frame. This works fine in the iPad simulator, but for some reason, when I run this on an actual device, when I turn trails on the particle trails flicker like there's something weird going on with the buffers.

Is there a better way to produce trails / why does this graphics problem only occur in the simulator?

Thanks!

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glClear() is called between buffers so that you can begin to draw the next one on a clean slate - you really need to clear the buffer between frames. Its not good practice to continue to fill up the buffer as you can start producing artifacts (as you are noticing).

To produce the trailing effect, you would probably want to use additional particles. Keep track of the particle's position or velocity, and then draw additional particles on the trail.