Hello Triangle: An OpenGL ES 2.0 Example
- Code Framework
- Where to Download the Examples
- Hello Triangle Example
- Building and Running the Examples
- Using the OpenGL ES 2.0 Framework
- Creating a Simple Vertex and Fragment Shader
- Compiling and Loading the Shaders
- Creating a Program Object and Linking the Shaders
- Setting the Viewport and Clearing the Color Buffer
- Loading the Geometry and Drawing a Primitive
- Displaying the Back Buffer
To introduce the basic concepts of OpenGL ES 2.0, we begin with a simple example. In this chapter, we show what is required to create an OpenGL ES 2.0 program that draws a single triangle. The program we will write is just about the most basic example of an OpenGL ES 2.0 application that draws geometry. There are number of concepts that we cover in this chapter:
- Creating an on-screen render surface with EGL.
- Loading vertex and fragment shaders.
- Creating a program object, attaching vertex and fragment shaders, and linking a program object.
- Setting the viewport.
- Clearing the color buffer.
- Rendering a simple primitive.
- Making the contents of the color buffer visible in the EGL window surface.
As it turns out, there are quite a significant number of steps required before we can start drawing a triangle with OpenGL ES 2.0. This chapter goes over the basics of each of these steps. Later in the book, we fill in the details on each of these steps and further document the API. Our purpose here is to get you running your first simple example so that you get an idea of what goes into creating an application with OpenGL ES 2.0.
Throughout the book, we will be building up a library of utility functions that form a framework of useful functions for writing OpenGL ES 2.0 programs. In developing example programs for the book, we had several goals for this code framework:
- It should be simple, small, and easy to understand. We wanted to focus our examples on the relevant OpenGL ES 2.0 calls and not on a large code framework that we invented. Rather, we focused our framework on simplicity and making the example programs easy to read and understand. The goal of the framework was to allow you to focus your attention on the important OpenGL ES 2.0 API concepts in each example.
- It should be portable. Although we develop our example programs on Microsoft Windows, we wanted the sample programs to be easily portable to other operating systems and environments. In addition, we chose to use C as the language rather than C++ due to the differing limitations of C++ on many handheld platforms. We also avoid using global data, something that is also not allowed on many handheld platforms.
As we go through the examples in the book, we introduce any new code framework functions that we use. In addition, you can find full documentation for the code framework in Appendix D. Any functions you see in the example code that are called that begin with es (e.g., esInitialize()) are part of the code framework we wrote for the sample programs in this book.