OpenGL ES programming guide for iOS Chapter 1

About OpenGL ES

Open graphics library(OpenGL) is used to visualize two-dimensional and three-dimensional data. It is a multi-purpose open standard graphics library that supports 2D and 3D digital content creation, mechanical and architectural design, virtual samples, flight simulation, games, and more applications. OpenGL allows application developers to configure 3D graphics pipelines and submit data. Vertices are convertible and illuminated, assemble original functions, and create 2D images. OpenGL is designed as a translation function to call graphics commands and send them to the underlying Graphics Device hardware.

Because the underlying hardware is dedicated to processing graphics commands, OpenGL plotting is very fast.

OpenGL for Embedded SystemsOpenGL ES is a simplified version of OpenGL. It eliminates redundancy and provides a library, which is easy to learn and practice on mobile devices.

 

Overview

Apple provides OpenGL ES 1.1 and OpenGL ES 2.0:

● OpenGL ES 1.1 implements a clear pipeline of fixed functions. It implements traditional lighting and shadow modes and allows configuration at each stage to perform special tasks or disable unwanted features.

● OpenGL ES 2.0 and OpenGL ES 1.1 have many common functions, but all functions related to fixed vertices and assembly line stages are removed. On the contrary, it provides new features for accessing the general coloring machine (shader) pipeline. The coloring tool allows you to customize the vertex and fragment functions and execute them directly on the graphic hardware. With the coloring tool, your application can more clearly customize the pipeline Input and calculation of each vertex and fragment.

 

Opengles is based on the C language,
Platform-independent application interfaces

Because opengles is a C-based application interface, it is very easy to transplant and widely supported. As a C application interface, it can be seamlessly integrated with the cocoatouch application based on objective-C. The window layer is not declared in the opengles specification. The main operating system must provide the function to create an opengles renderingcontext to accept commands and create a buffer to draw command results.

Related chapters"OpenGL ES on iOS"
(13 pages ),
"Processing OpenGL ES Contexts"
(20 pages)

Opengles is integrated into core Animation

Core animation is the basis of IOS graphics and contains OpenGL ES content displayed on the screen by applications. When you develop an OpenGL ES application, the OpenGL ES content is drawn in a special core animation layer, which is called a caeagllayer object. Images drawn using opengles are stored in caeagllayer. Coreanimation combines the graphic content of other layers and displays the final result on the screen.

Related chapters"Drawing with OpenGL ES"
(28 pages)