iPhone 3D Programming

Chapter 3. Vertices and Touch Points

Second star to the right…and straight on ’til morning.

—Peter Pan, J.M. Barrie

The iPhone has several input devices, including the accelerometer, microphone, and touchscreen, but your application will probably make the most use of the touchscreen. Since the screen has multitouch capabilities, your application can obtain a list of several touch points at any time. In a way, your 3D application is a “point processor”: it consumes points from the touchscreen and produces points (for example, triangle vertices) for OpenGL. So, I thought I’d use the same chapter to both introduce the touchscreen and cover some new ways of submitting vertices to OpenGL.

This chapter also covers some important best practices for vertex submission, such as the usage of vertex buffer objects. I would never argue with the great man who decreed that premature optimization is the root of all evil, but I want to hammer in good habits early on.

Toward the end of the chapter, you’ll learn how to generate some interesting geometry using parametric surfaces. This will form the basis for a fun demo app that you’ll gradually enhance over the course of the next several chapters.

Reading the Touchscreen

In this section, I’ll introduce the touchscreen API by walking through a modification of HelloCone that makes the cone point toward the user’s finger. You’ll need to change the name of the app from HelloCone to TouchCone, since the user now touches the cone instead of merely greeting it. ...