Hi Alex!
Well, unfortunately it's not exactly that way, at least on the iPhone.
On most desktop computers, the graphics card/chip has its own designated memory. So your PC might have 2GB of conventional RAM and 1GB of graphics RAM. On such a system, it works as you describe.
However, on the iPhone, there is only one block of memory that can be used either by the graphics chip or by the software. If you need more graphics memory, you will have less conventional memory available, and vice versa. (Starting with iPhone 3GS; I just read somewhere that the older models had 24MB of designated graphics memory).
But I think your "touch maps" won't necessarily need a lot of memory. Since users navigate with their fingers, they won't notice if the resolution of those images is only 1/10th or so of your graphics. And, as I said, you only need b/w images for those maps.
BTW, a good place for your touch tests will be the "hitTestPoint:" method, as shown in the "RoundButton" class of the demo.
Another tip: Using a texture atlas for as many of your textures as possible will be good for performance AND for graphics memory consumption. The reason for the latter is that OpenGL can only work with textures that have a width and height of the power of two (64x128, 256x256, etc.). Sparrow hides this fact from you, but whenever you create a texture, the next-biggest power-of-two texture will be created behind the scenes. (So, if your image is 60x100 pixel, Sparrow will create a 64x128 pixel texture). Thus, it's always a good idea to use an atlas.
Creating this atlas is very simple with Sparrow's atlas generator -- to be found in the SVN repository, or in the next Sparrow version. So you won't have much additional work to do.
Daniel
