Chapter 1 OpenGL es1.1.12

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Chapter 1

Introduction

This document describes the specific content of OpenGL ES graphics system, such as what kind of system it is and how it operates. We believe that readers already have basic knowledge about computer graphics. This means that readers should be familiar with the Important Algorithms of computer graphics, basic graphics hardware, and related content.

1.1 formatting of optional features)

Some features defined in the specification are optional, that is, they can be selectively provided when OpenGL ES is implemented. These optional functions are defined in the Specification first. The optional status table entries are displayed in a gray background.

1.2 OpenGL ES graphic system definition

OpenGL ES is a software interface of graphics hardware. These interfaces are composed of a series of processes and functions. Programmers can use these interfaces to define their objects and operations to generate high-quality graphic images and three-dimensional object color images.

Most OpenGL ES require that the graphic hardware have a frame cache. Most OpenGL ES calls can be used to draw points, lines, and polygon objects. However, in some cases, frame caching is still required when anti-sawtooth or texture functions are enabled. Even some OpenGL ES focus on frame control.

OpenGL es1.1 is based on openggl1.5 graphics system. It is designed to run an embedded and mobile device graphics hardware. It deletes a large number of redundant and expired functions, and adds some new features. In this specification, the differences between OpenGL ES and openggl are not described in detail, the file name is simply summarized in the document "OpenGL ES common/common-lite pro into Le speci into cation (difference speci into cation.

1.3 OpenGL ES graphics system profiles

This specification describes two profiles of OpenGL ES: Common and common lite. Many Commands are shared in two profiles, while some commands are only supported by one profile.

Unlike Common, common Lite is mainly used in simple graphics systems and does not support high-performance floating point operations. Common lite supports commands with fixed-point parameters, while common also supports commands with floating-point parameters.

The differences between the two profiles and the commands supported by only the common profile are collected in the corresponding sections in Appendix C and the specifications.

1.4 OpenGL ES from the programmer's perspective

For programmers, OpenGL ES is a set of commands that define a 2D and 3D geometric object and how to render these objects into the frame cache. OpenGL ES provides the immediate-mode interface, that is, defining an object will be drawn.

In a typical program using OpenGL ES, the call starts when a window is opened. This window is written to the frame cache by the current program, and then an OpenGL ES context and window-related call are allocated. The implementation of these steps sometimes uses a set of APIS, such as khronos native platform graph-icsinterface (EGL), and the documents are separated. Once the context is allocated, the programmer can use the OpenGL ES command freely. Some calls are used to draw simple geometric objects, such as points, lines, and polygon, while others can be used for rendering, including how to ignment and coloring, and how to switch from a user's two-dimensional or three-dimensional space to a two-dimensional screen. In addition, some calls directly manipulate the frame cache, such as reading pixels.

1.5 OpenGL ES from the perspective of implementers

For implementers, OpenGL ES is a set of commands that operate graphics hardware. If the hardware contains an accessible frame cache, OpenGL ES must implement all commands on the CPU of the host. In general, graphics hardware will include certain graphics acceleration, such as the complex floating point processor for rendering two-dimensional lines and polygon and the grating subsystem for processing geometric data conversion and computing. The task of OpenGL ES implementers is to provide the software interface of the CPU and strip each OpenGL ES command from the graphics hardware and CPU. The result of this peel-off is that when OpenGL ES is called, the graphic hardware must have the optimal performance.

OpenGL ES maintains a considerable amount of state information, which controls how objects write to the frame cache. Some of these statuses can be directly used by users. He/she can call related functions to obtain these status values. Some of these States are visible only when they are being painted. One major goal of this specification is to make the OpenGL ES state clearer and more explicit about how it changes and what it looks like.

1.6 our perspective

We regard OpenGL ES as a state machine, which controls a group of painting operations. The specifications generated by this model should meet the needs of programmers and implementers. However, it does not have to provide an implementation. An implementation must follow the agreed method. However, there may be other methods that are more effective than defined to implement a specific computing.