In general, 3D performance is often expressed as the number of polygons that can be rendered each second or as the number of times per second the screen is updated, i.e. the frame rate per second (fps). On a standard PC system there is a clear relationship between these two numbers; if you lower the number of polygons to be drawn on the screen, the fps increases.

On a mobile phone, with its limited processor speed, another factor becomes important as well. Besides the number of polygons, the number of pixels that has to be drawn also has a huge impact on the fps. This means that 10 small polygons sometimes can be drawn faster than 5 big ones, somewhat complicating the relationship between number of polygons and fps mentioned above.

The conclusion is that you have to take great care, not only of the number of polygons used, but also of how big a screen estate they use.

The downloadable JSR-184 MIDlet shows this behavior. It displays a rotating 3D object that changes size, but not the number of polygons, when you press the right softkey. Note how the fps changes depending on the number of pixels that has to be drawn.

Download JSR-184 RenderFigure code sample>>