iPhone 3D Programming

Chapter 5. Textures and Image Capture

Not everybody trusts paintings, but people believe photographs.

—Ansel Adams

Shading algorithms are required for effects that need to respond to a changing condition in real time, such as the movement of a light source. But procedural methods can go only so far on their own; they can never replace the creativity of a professional artist. That’s where textures come to the rescue. Texturing allows any predefined image, such as a photograph, to be projected onto a 3D surface.

Simply put, textures are images; yet somehow, an entire vocabulary is built around them. Pixels that make up a texture are known as texels. When the hardware reads a texel color, it’s said to be sampling. When OpenGL scales a texture, it’s also filtering it. Don’t let the vocabulary intimidate you; the concepts are simple. In this chapter, we’ll focus on presenting the basics, saving some advanced techniques for later in this book.

We’ll begin by modifying ModelViewer to support image loading and simple texturing. Afterward we’ll take a closer look at some of the OpenGL features involved, such as mipmapping and filtering. Toward the end of the chapter we’ll use texturing to perform a fun trick with the iPhone camera.

Adding Textures to ModelViewer

Our final enhancement to ModelViewer wraps a simple grid texture around each of the surfaces in the parametric gallery, as shown in Figure 5-1. We need to store only one cell of the grid in an image file; OpenGL can repeat the source pattern ...